Network Working Group K. Sriram, Ed. Internet-Draft USA NIST Intended status: Informational July 4, 2016 Expires: January 5, 2017 BGPSEC Design Choices and Summary of Supporting Discussions draft-sriram-bgpsec-design-choices-10 Abstract This document has been written to capture the design rationale for the individual draft-00 version of BGPSEC protocol specification (I- D.lepinski-bgpsec-protocol-00). It lists the decisions that were made in favor of or against each design choice, and presents brief summaries of the arguments that aided the decision process. A similar document can be published in the future as the BGPSEC design discussions make further progress and additional design considerations are discussed and finalized. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on January 5, 2017. Copyright Notice Copyright (c) 2016 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must Sriram Expires January 5, 2017 [Page 1] Internet-Draft BGPSEC Design Choices July 2016 include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Creating Signatures and the Structure of BGPSEC Update Messages . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1. Origin Validation Using ROA . . . . . . . . . . . . . . . 4 2.2. Attributes Signed by an Originating AS . . . . . . . . . 4 2.3. Attributes Signed by an Upstream AS . . . . . . . . . . . 5 2.4. What Attributes Are Not Signed . . . . . . . . . . . . . 6 2.5. Receiving Router Actions . . . . . . . . . . . . . . . . 6 2.6. Prepending of ASes in AS Path . . . . . . . . . . . . . . 7 2.7. What RPKI Data Need be Included in Updates . . . . . . . 8 3. Withdrawal Protection . . . . . . . . . . . . . . . . . . . . 8 3.1. Withdrawals Not Signed . . . . . . . . . . . . . . . . . 8 3.2. Signature Expire Time for Withdrawal Protection (a.k.a. Mitigation of Replay Attacks) . . . . . . . . . . . . . . 9 3.3. Should Route Expire Time be Communicated in a Separate Message . . . . . . . . . . . . . . . . . . . . . . . . . 10 3.4. Effect of Expire-Time Updates in BGPSEC on RFD . . . . . 11 4. Signature Algorithms and Router Keys . . . . . . . . . . . . 13 4.1. Signature Algorithms . . . . . . . . . . . . . . . . . . 13 4.2. Agility of Signature Algorithms . . . . . . . . . . . . . 13 4.3. Sequential Aggregate Signatures . . . . . . . . . . . . . 14 4.4. Protocol Extensibility . . . . . . . . . . . . . . . . . 15 4.5. Key Per Router (Rouge Router Problem) . . . . . . . . . . 16 4.6. Router ID . . . . . . . . . . . . . . . . . . . . . . . . 16 5. Optimizations and Resource Sizing . . . . . . . . . . . . . . 16 5.1. Update Packing and Repacking . . . . . . . . . . . . . . 17 5.2. Signature Per Prefix vs. Signature Per Update . . . . . . 17 5.3. Max PDU Size and PDU Negotiation . . . . . . . . . . . . 18 5.4. Temporary Suspension of Attestations and Validations . . 19 6. Incremental Deployment and Negotiation of BGPSEC . . . . . . 19 6.1. Downgrade Attacks . . . . . . . . . . . . . . . . . . . . 20 6.2. Inclusion of Address Family in Capability Advertisement . 20 6.3. Incremental Deployment: Capability Negotiation . . . . . 20 6.4. Partial Path Signing . . . . . . . . . . . . . . . . . . 21 6.5. Consideration of Stub ASes with Resource Constraints: Encouraging Early Adoption . . . . . . . . . . . . . . . 21 6.6. Proxy Signing . . . . . . . . . . . . . . . . . . . . . . 23 6.7. Multiple Peering Sessions Between ASes . . . . . . . . . 24 7. Interaction of BGPSEC with Common BGP Features . . . . . . . 24 7.1. Peer Groups . . . . . . . . . . . . . . . . . . . . . . . 24 7.2. Communities . . . . . . . . . . . . . . . . . . . . . . . 25 7.3. Consideration of iBGP Speakers and Confederations . . . . 25 Sriram Expires January 5, 2017 [Page 2] Internet-Draft BGPSEC Design Choices July 2016 7.4. Consideration of Route Servers in IXPs . . . . . . . . . 26 7.5. Proxy Aggregation (a.k.a. AS_SETs) . . . . . . . . . . . 27 7.6. 4-Byte AS Numbers . . . . . . . . . . . . . . . . . . . . 27 8. BGPSEC Validation . . . . . . . . . . . . . . . . . . . . . . 28 8.1. Sequence of BGPSEC Validation Processing in a Receiver . 28 8.2. Signing and Forwarding Updates when Signatures Failed Validation . . . . . . . . . . . . . . . . . . . . . . . 29 8.3. Enumeration of Error Conditions . . . . . . . . . . . . . 29 8.4. Procedure for Processing Unsigned Updates . . . . . . . . 30 8.5. Response to Syntactic Errors in Signatures and Recommendation for Reaction . . . . . . . . . . . . . . . 31 8.6. Enumeration of Validation States . . . . . . . . . . . . 32 8.7. Mechanism for Transporting Validation State through iBGP 33 9. Operational Considerations . . . . . . . . . . . . . . . . . 35 9.1. Interworking with BGP Graceful Restart . . . . . . . . . 35 9.2. BCP Recommendations for Minimizing Churn: Certificate Expiry/Revocation and Signature Expire Time . . . . . . . 36 9.3. Outsourcing Update Validation . . . . . . . . . . . . . . 36 9.4. New Hardware Capability . . . . . . . . . . . . . . . . . 36 9.5. Signed Peering Registrations . . . . . . . . . . . . . . 37 10. Co-authors . . . . . . . . . . . . . . . . . . . . . . . . . 37 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 38 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 38 13. Security Considerations . . . . . . . . . . . . . . . . . . . 38 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 38 14.1. Normative References . . . . . . . . . . . . . . . . . . 38 14.2. Informative References . . . . . . . . . . . . . . . . . 39 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 42 1. Introduction The goal of BGPSEC effort is to enhance the security of BGP by enabling full AS path validation based on cryptographic principles. Work on prefix-origin validation based on a Resource certificate PKI (RPKI) is already nearing completion in the IETF SIDR WG. The BGPSEC effort is aimed at taking advantage of the same RPKI infrastructure developed in the SIDR WG to add cryptographic signatures to BGP updates, so that routers can perform full AS path validation [RFC7132] [RFC7353] [I-D.ietf-sidr-bgpsec-overview] [I-D.ietf-sidr-bgpsec-protocol]. The key high-level design goals of BGPSEC protocol are as follow [RFC7353]: o Rigorous path validation for all announced prefixes; not merely showing that a path is not impossible. o Incremental deployment capability; no flag-day requirement for global deployment. o Protection of AS paths only in inter-domain routing (eBGP); not applicable to iBGP (or to IGPs). Sriram Expires January 5, 2017 [Page 3] Internet-Draft BGPSEC Design Choices July 2016 o Aim for no increase in provider's data exposure (e.g., require no disclosure of peering relations, etc). This document is a companion to the earliest version of the BGPSEC protocol specification submitted as individual draft-00 [I-D.lepinski-bgpsec-protocol], and is intended to provide design justifications for this initial BGPSEC specification. This document lists the decisions that were made in favor of or against various design choices, and presents brief summaries of the discussions that weighed in the pros and cons and aided the decision process. A similar document can be published in the future as the BGPSEC design discussions make further progress and additional design considerations are discussed and finalized. The design choices and discussions are presented under the following eight broad categories (with many subtopics within each category): (1) Creating Signatures and the Structure of BGPSEC Update Messages, (2) Withdrawal Protection, (3) Signature Algorithms and Router Keys, (4) Optimizations and Resource Sizing, (5) Incremental Deployment and Negotiation of BGPSEC, (6) Interaction of BGPSEC with Common BGP Features, (7) BGPSEC Validation, and (8) Operational Considerations. 2. Creating Signatures and the Structure of BGPSEC Update Messages 2.1. Origin Validation Using ROA 2.1.1. Decision Prefix-Origin validation using Route Origin Authorization (ROA) is necessary and complements AS path attestation based on signed updates. Thus the BGPSEC design makes use of the origin AS validation capability provided by the RPKI. 2.1.2. Discussion Prefix-Origin validation using RPKI constructs as developed in the IETF SIDR WG is a necessary component of BGPSEC, i.e., it provides cryptographic validation that the first hop AS is authorized to originate a route for the prefix in question. 2.2. Attributes Signed by an Originating AS 2.2.1. Decision An originating AS will sign over the NLRI length, NLRI prefix, its own ASN, the next ASN, the signature algorithm suite ID, and a signature Expire Time (see Section 3.2) for the update. The update Sriram Expires January 5, 2017 [Page 4] Internet-Draft BGPSEC Design Choices July 2016 signatures will be carried in a new optional, non-transitive BGP attribute. 2.2.2. Discussion The next hop ASN is included in the data covered by the signature. Without that the AS path cannot be secured; for example, it can be shortened (by a MITM) without being detected. It was decided that only the originating AS needs to insert a signature Expire Time in the update, as it is the originator of the route. The origin AS also will re-originate, i.e., beacon, the update prior to the Expire Time of said advertisement (see Section 3.2). (For an explanation of why upstream ASes do not insert their respective signature Expire Times, please see Section 3.2.2.) It was decided that each signed update would include only one NLRI prefix. If more than one NLRI prefix were included, and an upstream AS elected to propagate the advertisement for a subset of the prefixes, then the signature(s) on the update would break (see Section 5.1 and Section 5.2). If a mechanism were employed to preserve prefixes that were dropped, this would reveal info to later ASes that is not revealed in normal BGP operation. Thus a tradeoff was made to preserve the level of route info exposure that is intrinsic to BGP over the performance hit implied by limiting each update to carry only one prefix. The signature data is carried in an optional, non-transitive BGP attribute. The attribute is optional because this is the standard mechanism available in BGP to propagate new types of data. It was decided that the attribute should be non-transitive because of concern that the impact of sending the (potentially large) signatures to routers that don't understand them. Also, if a router that doesn't understand BGPSEC somehow gets a message with the signatures attribute then it would be undesirable for that router to forward the signatures to all of its neighbors, especially those who do not understand BGPSEC, and who may choke badly if they receive a very large optional BGP attribute. 2.3. Attributes Signed by an Upstream AS In the context of BGPSEC and throughout this document, an "upstream AS" simply refers to an AS that is further along in an AS path (origin AS being the nearest to a prefix). In principle, an AS that is upstream from an originating AS would sign the combined information including the NLRI length, NLRI prefix, AS path, next ASN, signature algorithm suite ID, and Expire Time. There are multiple choices for what is actually signed by an upstream AS: (1) Sriram Expires January 5, 2017 [Page 5] Internet-Draft BGPSEC Design Choices July 2016 Sign over the combination of NLRI length, NLRI prefix, AS path, next ASN, signature algorithm suite ID, and Expire Time; or (2) Sign over just the combination of previous signature (i.e., signature of the neighbor AS who forwarded the update) and next ASN; or (3) Sign over everything that was received from preceding AS plus next ASN; thus, ASi signs over NLRI length, NLRI prefix, signature algorithm suite ID, Expire Time, {ASi, AS(i-1), AS(i-2), ..., AS2, AS1}, AS(i+1)(i.e., next ASN), and {Sig(i-1), Sig(i-2), ..., Sig2, Sig1}. 2.3.1. Decision It was decided that that Method 2 will be used. Please see [I-D.lepinski-bgpsec-protocol] for additional protocol details and syntax. 2.3.2. Discussion The rationale for this choice (Method 2) was as follows. Signatures are performed over hash blocks. When the number of bytes to be signed exceeds one hash block, then the remaining bytes will overflow into a second hash block, which results in performance penalty. So it is advantageous to minimize the number of bytes being hashed. Also, an analysis of the three options noted above did not indentify any vulnerabilities associated with this approach. 2.4. What Attributes Are Not Signed 2.4.1. Decision Any attributes other than those identified in Section 2.2 and Section 2.3 are not signed. Examples of such attributes are Community Attribute, NO-EXPORT Attribute, Local_Pref, etc. 2.4.2. Discussion The above stated attributes that are not signed are viewed as local (e.g., do not need to propagate beyond next hop) or lack clear security needs. NO-EXPORT is sent over a secured next-hop and does not need signing. BGPSEC design should work with any transport layer protections. It is well understood that the transport layer must be protected hop by hop (if only to prevent malicious session termination). 2.5. Receiving Router Actions Sriram Expires January 5, 2017 [Page 6] Internet-Draft BGPSEC Design Choices July 2016 2.5.1. Decision The expected router actions on receipt of a signed update are described by the following example. Consider an update that was originated by AS1 with NLRI prefix p and has traversed the AS path [AS(i-1) AS(i-2) .... AS2 AS1] before arriving at ASi. Let the Expire Time (inserted by AS1) for the signature in this update be denoted as Te. Let AlgID represent the ID of the signature algorithm suite that is in use. The update is to be processed at ASi and possibly forwarded to AS(i+1). Let the attestations (signatures) inserted by each router in the AS path be denoted by Sig1, Sig2, ..., Sig(i-2), and Sig(i-1) corresponding to AS1, AS2, ... , AS(i-2), and AS(i-1), respectively. The method (#2 in Section 2.3) selected for signing requires a receiving router in ASi to perform the following actions: o Validate the prefix-origin pair (p, AS1) by performing a ROA match. o Verify that Te is greater than the clock time at the router performing these checks. o Check Sig1 with inputs {NLRI length, p, AlgID, Te, AS1, AS2}. o Check Sig2 with inputs {Sig1, AS3}. o Check Sig3 with inputs {Sig2, AS4}. o ... o ... o Check Sig(i-2) with inputs {Sig(i-3), AS(i-1)}. o Check Sig(i-1) with inputs {Sig(i-2), ASi}. o If the route that has been verified is selected as the best path (for prefix p), then generate Sig(i) with inputs {Sig(i-1), AS(i+1)}, and generate an update including Sig(i) to AS(i+1). 2.5.2. Discussion See Section 8.1 for suggestions regarding efficient sequencing of BGPSEC validation processing in a receiving router. Some or all of the validation actions may be performed by an off-board server (see Section 9.3). 2.6. Prepending of ASes in AS Path 2.6.1. Decision Prepending will be allowed. Prepending is defined as including more than one instance of the AS number of the router that is signing the update. Sriram Expires January 5, 2017 [Page 7] Internet-Draft BGPSEC Design Choices July 2016 2.6.2. Discussion The draft-00 version of the protocol specification calls for a signature to be associated with each prepended AS. The optimization of having just one signature for multiple prepended ASes will be pursued later (i.e., beyond draft-00 specification). If such optimization is used, a replication count would be included (in the signed update) to specify how many times an AS was prepended. 2.7. What RPKI Data Need be Included in Updates 2.7.1. Decision Concerning inclusion of RPKI data in an update, it was decided that only the Subject Key Identifier (SKI) of the router cert must be included in a signed update. This info identifies the router certificate, based on the SKI generation criteria defined in [RFC6487]. 2.7.2. Discussion It was discussed if each router public key certificate should be included in a signed update. Inclusion of this information might be helpful for routers that do not have access to RPKI servers or temporarily lose connectivity to them. It is safe to assume that in majority of network environments, intermittent connectivity would not be a problem. So it is best to avoid this complexity because majority of the use environments do not have connectivity constraints. Because the SKI of a router certificate is a hash of the public key of that certificate, it suffices to select the public key from that certificate. This design assumes that each BGPSEC router has access to a cache containing the relevant data from (validated) router certificates. 3. Withdrawal Protection 3.1. Withdrawals Not Signed 3.1.1. Decision Withdrawals are not signed. 3.1.2. Discussion In the current BGP protocol, any AS can withdraw, at any time, any prefix it previously announced. The rationale for not signing withdrawals is that BGPSEC assumes use of transport security between neighboring BGPSEC routers. Thus no external entity can inject an Sriram Expires January 5, 2017 [Page 8] Internet-Draft BGPSEC Design Choices July 2016 update that withdraws a route, or replay a previously transmitted update containing a withdrawal. Because the rationale for withdrawing a route is not visible to a neighboring BGPSEC router, there are residual vulnerabilities associated with withdrawals. For example, a router that advertised a (valid) route may fail to withdraw that route when it is no longer viable. A router also might re-advertise a route that it previously withdrew, before the route is again viable. This latter vulnerability is mitigated by the Expire Time value in an AS path signature (see Section 3.2). Repeated withdrawals and announcements for a prefix can run up the BGP RFD penalty and may result in unreachability for that prefix at upstream routers. But what can the attacker gain from doing so? This phenomenon is intrinsic to the design and operation of RFD. 3.2. Signature Expire Time for Withdrawal Protection (a.k.a. Mitigation of Replay Attacks) 3.2.1. Decision Only the originating AS inserts a signature Expire Time in the update; all other ASes along an AS path do not insert Expire Times associated with their respective signatures. Further, the originating AS will re-originate a route sufficiently in advance of the Expire Time of its signature so that other ASes along an AS path will typically receive the re-originated route well ahead of the current Expire Time for that route. The duration of the signature Expire Time is recommended to be on the order of days (preferably) but it may be on the order of hours (about 4 to 8 hours) in some cases, where extra replay protection is percieved to be critical. Each AS should stagger the Expire Time values in the routes it originates. Re-origination will be done, say, at time Tb after origination or the last re-origination, where Tb will equal a certain percentage of the Expire Time, Te (for example, Tb = 0.75 x Te). The percentage will be configurable and additional guidance can be provided via an operational considerations document later. Further, the actual re-origination time ought to be jittered with a uniform random distribution over a short interval {Tb1, Tb2} centered at Tb. It is also recommended that a receiving BGPSEC router should detect if the only attribute change in an announcement (relative to the current best path) is the expire time (besides, of course, the signatures). In that case, assuming that the update is found valid, the route processor should not re-announce the route to BGP-4 only (i.e., non-BGPSEC) peers. (It still has to sign and re-announce the Sriram Expires January 5, 2017 [Page 9] Internet-Draft BGPSEC Design Choices July 2016 route to BGPSEC speakers.) This procedure will reduce BGP chattiness for the non-BGPSEC border routers. 3.2.2. Discussion Mitigation of (update) replay attacks can be thought of as protection against malicious re-advertisement of withdrawn routes. If each AS along a path were to insert its own signature Expire Time, then there would be much additional BGP chattiness and increase in BGP processing load due to the need to detect and react to multiple (possibly redundant) signature Expire Times. Furthermore, there would be no extra benefit from the point of view of mitigation of replay attacks as compared to having a single Expire Time corresponding to the signature of the originating AS. The recommended Expire Time value is on the order of days but 4 to 8 hours may used in some cases on the basis of percieved need for extra protection from replay attacks. Thus, different ASes may choose different values based on the perceived need to protect against route replays. (A shorter Expire Time reduces the window during which an AS can replay the route, even if the route has been withdrawn by a downstream AS. However, shorter Expire Time values cause routes to be refreshed more often, and thus causes more BGP chatter.) Even a 4 hours duration seems adequate to keep the re-origination workload manageable. For example, if 500K routes are re-originated every 4 hours, it amounts to an increase in BGP update load of at least 35 updates per second; this can be considered reasonable. However, further analysis is needed to confirm these recommendations. It was stated above that originating AS will re-originate a route sufficiently in advance of its Expire Time. What is considered sufficiently in advance? For this, modeling should be performed to determine the 95th-percentile convergence time of update propagation in BGPSEC enabled Internet. Each BGPSEC router should stagger the Expire Time values in the updates it originates, especially during table dumps to a neighbor or during its own recovery from a BGP session failure. By doing this, the re-origination (i.e., beaconing) workload at the router will be dispersed. 3.3. Should Route Expire Time be Communicated in a Separate Message 3.3.1. Decision The idea of sending a new signature expire time in a special message (rather than re-transmitting the entire update with signatures) was considered. However, it was decided not to do this. Re-origination Sriram Expires January 5, 2017 [Page 10] Internet-Draft BGPSEC Design Choices July 2016 to communicate a new signature Expire Time will be done by propagation of a normal update message; no special type of message will be required. 3.3.2. Discussion It was suggested that if re-beaconing of signature Expire Time is carried in a separate special message, then update processing load may be reduced. But it was recognized that such re-beaconing message necessarily entails AS path and prefix information, and hence cannot be separated from the update. It was observed that at the edge of the Internet, there are frequent updates that may result from simple situations like BGP session being switched from one interface to another (e.g., from primary to backup) between two peering ASes (e.g., customer and provider). With BGP-4, these updates do not propagate beyond the two ASes involved. But with BGPSEC, the customer AS will put in a new signature Expire Time each time such an event happens, and hence the update will need to propagate throughout the Internet (limited only by best path selection process). It was accepted that this cost of added churn will be unavoidable. 3.4. Effect of Expire-Time Updates in BGPSEC on RFD 3.4.1. Decision With regard to the Route Flap Damping (RFD) protocol [RFC2439][JunOS][CiscoIOS], no differential treatment is required for Expire-Time triggered (re-beaconed) BGPSEC updates. However, it was noted that it would be preferable if these updates did not cause route churn (and perhaps not even require any RFD related processing), since they are identical except for the change in the Expire Time value. The way this can be accomplished is by not assigning RFD penalty to Expire-Time triggered updates. If the community agrees, this could be accommodated, but a change to the BGP-RFD protocol specification will be required. 3.4.2. Discussion Summary: The decision is supported by the following observations: (1) Expire Time-triggered updates are generally not preceded by withdrawals, and hence the path hunting and associated RFD exacerbation [Mao02][RIPE580] problems are not anticipated; (2) Such updates would not normally change the best path (unless another concurrent event Sriram Expires January 5, 2017 [Page 11] Internet-Draft BGPSEC Design Choices July 2016 impacts the best path); (3) Expire Time-triggered updates would have negligible impact on RFD penalty accumulation because the re- advertisement interval is much longer relative to the half-time of decay of RFD penalty. Elaborating further on reason #4 above, it may be noted that the re-advertisements (i.e., beacons) of a route for a given address prefix from a given peer will be received at intervals of a few or several hours (see Section 3.2). During that time period, any incremental contribution to RFD penalty due to a Expire Time-triggered update would decay sufficiently to have negligible (if any) impact on damping of said address prefix. Additional details of this analysis and justification can be found below. Further Details of the Analysis and Justification: The frequency with which RFD penalty increments may be triggered for a given prefix from a given peer is the same as the re-beaconing frequency for that prefix from its origin AS. The re-beaconing frequency is on the order of once every few or several hours (see Section 3.2). The incremental RFD penalty assigned to a prefix due to a re-beaconed update varies depending on the implementation. For example, it appears that JunOS implementation [JunOS] would assign a penalty of 1000 or 500 depending on whether the re-beaconed update is regarded as a re-advertisement or an attribute change, respectively. Normally, a re-beaconed update would be treated as a case of attribute change. The Cisco implementation [CiscoIOS] on the other hand assigns an RFD penalty only in the case of an actual flap (i.e., a route is available, then unavailable, or vice versa). So it appears that Cisco implementation of RFD would not assign any penalty for a re-beaconed update (i.e., a route was already advertised previously; not withdrawn; and the re-beaconed update is merely updating the expire time attribute). Even if one assumes that an RFD penalty of 500 is assigned (corresponding to attribute change in JunOS RFD implementation), it can be illustrated that the incremental affect it would have on damping the prefix in consideration would be negligible. The reason for this is as follows. The half-time of RFD penalty decay is normally set to 15 minutes, whereas the re-beaconing frequency is on the order of once every few or several hours. An incremental penalty of 500 would decay to 31.25 in one hour; 0.12 in two hours; 3x10^(-5) in three hours. It may also be noted that the threshold for route suppression is 3000 in JunOS and 2000 in Cisco IOS. Based on the foregoing analysis, it may be concluded that routine re-beaconing by itself would not result in RFD suppression of routes in the BGPSEC protocol. Sriram Expires January 5, 2017 [Page 12] Internet-Draft BGPSEC Design Choices July 2016 4. Signature Algorithms and Router Keys 4.1. Signature Algorithms 4.1.1. Decision Initially, 256-bit ECDSA with SHA-256 will be used. One other algorithm, e.g., 256-bit DSA also will be used during prototyping and testing. The use of a second algorithm is needed to verify the ability of the BGPSEC implementations to change from a current algorithm to the next algorithm. 4.1.2. Discussion Initially, choice of 2048-bit RSA algorithm for BGPSEC update signatures was considered because it is being used ubiquitously in the RPKI system. However, use of ECDSA-256 algorithm was decided because it yields a smaller signature size, so that the RIB sizes needed for BGPSEC would be much smaller [RIB_size]. Testing with two different signature algorithms (256-bit ECDSA and 256-bit RSA) for transition from one to the other will increase confidence in the prototyped protocol. For Elliptic Curve Cryptography (ECC) algorithms, according to [RFC6090], optimizations and specialized algorithms (e.g., for speed- ups) have active IPR, but the basic (un-optimized) algorithms do not have IPR encumbrances. 4.2. Agility of Signature Algorithms 4.2.1. Decision During the transition period from one algorithm, i.e., current algorithm, to the next (new) algorithm, the updates will carry two sets of signatures (i.e., two Signature-List Blocks), one corresponding to each algorithm. Each Signature-List Block will be preceded by its type-length field and an algorithm-suite identifier. A BGPSEC speaker that has been upgraded to handle the new algorithm should validate both Signature-List Blocks, and then add its corresponding signature to each Signature-List Block for forwarding the update to the next AS. A BGPSEC speaker that has not been upgraded to handle the new algorithm will strip off the Signature- List Block of the new algorithm, and forward the update after adding its own sig to the Signature-List Block of the current algorithm. It was decided that there will be at most two Signature-List Blocks per update. Sriram Expires January 5, 2017 [Page 13] Internet-Draft BGPSEC Design Choices July 2016 4.2.2. Discussion A length field in the Signature-List Block allows for delineation of the two signature blocks. Hence, a BGPSEC router that doesn't know about a particular algorithm suite (and hence doesn't know how long signatures were for that algorithm suite) could still skip over the corresponding Signature-List Block when parsing the message. The overlap period between the two algorithms is expected to last two to four years. The RIB memory and cryptographic processing capacity will have to be sized to cope with such overlap periods when updates would contain two sets of sigs [RIB_size]. The lifetime of a signature algorithm is anticipated to be much longer than the duration of a transition period from current to new algorithm. It is fully expected that all ASes will have converted to the required new algorithm within a certain amount of time that is much shorter than the interval in which a subsequent newer algorithm may be investigated and standardized for BGPSEC. Hence, the need for more than two Signature-List Blocks per update is not envisioned. 4.3. Sequential Aggregate Signatures 4.3.1. Decision There is currently weak or no support for the Sequential Aggregate Signature (SAS) approach. Please see in the discussion section below for a brief description of what SAS is and what its pros and cons are. 4.3.2. Discussion In Sequential Aggregate Signature (SAS) method, there would be only one (aggregated) signature per signature block, irrespective of the number of AS hops. For example, ASn (nth AS) takes as input the signatures of all previous ASes [AS1, ..., AS(n-1)] and produces a single composite signature. This composite signature has the property that a recipient who has the public keys for AS1, ..., ASn can verify (using only the single composite signature) that all of the ASes actually signed the message. SAS could potentially result in savings in bandwidth, PDU size, and maybe in RIB size but the signature generation and validation costs will be higher as compared to one signature per AS hop. SAS schemes exist in the literature, typically based on RSA or equivalent. In order to do SAS with RSA, and based on the algorithm choices already adopted for the RPKI, a 2048-bit signature size would be required. Without SAS, a DSA with 320- bit signature (1024-bit Sriram Expires January 5, 2017 [Page 14] Internet-Draft BGPSEC Design Choices July 2016 key) or ECDSA with 512-bit signature (256-bit key) would suffice, for equivalent cryptographic strength. The larger signature size of RSA used with SAS undermines the advantages of SAS, because the average hop count, i.e., number of ASes, for a route is about 3.8. In the end, it may turn out that SAS has more complexity and does not provide sufficient savings in PDU size or RIB size to merit its use. Further exploration of this is needed to better understand SAS properties and applicability for BGPSEC. There is also a concern that SAS is not a time-tested cryptographic technique and thus its adoption is potentially risky. 4.4. Protocol Extensibility There is a clearly a need to specify a transition path from a current protocol specification to a new version. When changes to the processing of the BGPSEC_Path_Signatures are required, that will require for a new version of BGPSEC. Examples of this include changes to the data that is protected by the BGPSEC signatures or adoption of a signature algorithm in which the number of signatures in the Signature-List Block may not correspond to one signature per AS in the AS-PATH (e.g., aggregate signatures). 4.4.1. Decision The protocol-version transition mechanism here is analogous to the algorithm transition discussed in Section 4.2. During the transition period from one protocol version (i.e., current version) to the next (new) version, updates will carry two sets of signatures (i.e., two Signature-List Blocks), one corresponding to each version. A protocol-version identifier is included with each Signature-List Block. Hence, each Signature-List Block will be preceded by its type-length field and a protocol-version identifier. A BGPSEC speaker that has been upgraded to handle the new version should validate both Signature-List Blocks, and then add its corresponding signature to each Signature-List Block for forwarding the update to the next AS. A BGPSEC speaker that has not been upgraded to handle the new protocol version will strip off the Signature-List Block of the new version, and forward the update with an attachment of its own signature to the Signature-List Block of the current version. 4.4.2. Discussion In the case that change to BGPSEC is deemed desirable, it is expected that a subsequent version of BGPSEC would be created and that this version of BGPSEC would specify a new BGP Path Attribute, let's call it BGPSEC_PATH_SIG_TWO, which is designed to accommodate the desired changes to BGPSEC. At this point a transition would begin which is analogous to the algorithm transition discussed in Section 4.2. Sriram Expires January 5, 2017 [Page 15] Internet-Draft BGPSEC Design Choices July 2016 During the transition period all BGPSEC speakers will simultaneously include both the BGPSEC_PATH_SIGNATURES (curent) attribute and the new BGPSEC_PATH_SIG_TWO attribute. Once the transition is complete, the use of BGPSEC_PATH_SIGNATURES could then be deprecated, at which point BGPSEC speakers will include only the new BGPSEC_PATH_SIG_TWO attribute. Such a process could facilitate a transition to a new BGPSEC semantics in a backwards compatible fashion. 4.5. Key Per Router (Rouge Router Problem) 4.5.1. Decision Within each AS, each individual BGPSEC router can have a unique pair of private and public keys. 4.5.2. Discussion If a router is compromised, its key pair can be revoked independently, without disrupting the other routers in the AS. Each per-router key-pair will be represented in an end-entity certificate issued under the CA cert of the AS. The Subject Key Identifier (SKI) in the signature points to the router certificate (and thus the unique public key) of the router that affixed its signature, so that a validating router can reliably identify the public key to use for signature verification. 4.6. Router ID 4.6.1. Decision The router certificate Subject name will be the string "router" followed by a decimal representation of a 4-byte AS number followed by the router ID. See the current RFCs for preferred standard textual representations for 4-byte ASNs [RFC5396] and router IDs [RFC6891]. 4.6.2. Discussion Every X.509 certificate requires a Subject name. The stylized Subject name adopted here is intended to facilitate debugging, by including the ASN and router ID. 5. Optimizations and Resource Sizing Sriram Expires January 5, 2017 [Page 16] Internet-Draft BGPSEC Design Choices July 2016 5.1. Update Packing and Repacking In the current BGP protocol (BGP-4) operation [RFC4271], an originating BGP router normally packs multiple prefix (NLRI) announcements into one update if the prefixes all share the same BGP attributes. When an upstream BGP router forwards eBGP updates to its peers, it can also pack multiple prefixes (based on shared AS path and attributes) into one update. The update propagated by the upstream BGP router may include only a subset of the prefixes that were packed in a received update. 5.1.1. Decision The initial draft-00 BGPSEC specification [I-D.lepinski-bgpsec-protocol] does not accommodate update packing. Each update contains exactly one prefix. This avoids the complexity that would be otherwise inevitable if the origin had packed and signed multiple prefixes in an update and an upstream AS decided to propagate an update containing only a subset of the prefixes in that update. BGPSEC recommendation regarding packing and repacking will be revisited when optimizations are considered in the future. 5.1.2. Discussion Currently, with BGP-4, there are, on average, approximately 4 prefixes announced per update [RIB_size]. So the number of BGP updates (carrying announcements) is about 4 times fewer, on average, as compared to the number of prefixes announced. The current decision is to include only one prefix per secured update (see Section 2.2 and Section 2.3). When optimizations are considered in the future, the possibility of packing multiple prefixes into an update can be considered. (Please see Section 5.2 for a discussion of signature per prefix vs. signature per update.) Repacking could be performed if signatures were generated on a per prefix basis. However, one problem regarding this approach, i.e., multiple prefixes in a BGP update but with a separate signature for each prefix, is that the resuting BGP update violates the basic definition of a BGP update. That is becuase the different prefixes will have different signature and expire-time attibutes, while a BGP update (by definition) must have the same set of shared attributes for all prefixes it carries. 5.2. Signature Per Prefix vs. Signature Per Update Sriram Expires January 5, 2017 [Page 17] Internet-Draft BGPSEC Design Choices July 2016 5.2.1. Decision The initial design calls for including exactly one prefix per update, hence there is only one signature in each secured update (modulo algorithm transition conditions). Optimizations will be examined later. 5.2.2. Discussion Some notes to assist in future optimization discussions: In the general case of one signature per update, multiple prefixes may be signed with one signature together with their shared AS path, next ASN, and Expire Time. If signature per update is used, then there are potentially savings in update PDU size as well as RIB memory size. But if there are any changes made to the announced prefix set along the AS path, then the AS where the change occurs would need to insert an Explicit Path Attribute (EPA)[I-D.draft-clynn-s-bgp]. The EPA conveys information regarding what the prefix set contained prior to the change. There would be one EPA for each AS that made such a modification, and there would be a way to associate each EPA with its corresponding AS. This enables an upstream AS to be able to know and to verify what was announced and signed by prior ASs in the AS path (in spite of changes made to the announced prefix set along the way). The EPA adds complexity to processing (signature generation and validation), further increases the size of updates and, thus of the RIB, and exposes data to downstream ASes that would not otherwise be exposed. Not all the pros and cons of packing and repacking in the context of signature per prefix vs. signature per update (with packing) have been evaluated. But the current recommendation is for having only one prefix per update (no packing); so there is no need for the EPA attribute. 5.3. Max PDU Size and PDU Negotiation The current BGP-4 update PDU size is limited to 4096 bytes (4KB). The probability of exceeding the current max PDU size of 4KB will be higher for BGPSEC as compared to that for BGP-4 [RIB_size]. Hence, there is need for adopting a higher max PDU size for BGPSEC. 5.3.1. Decision The current thinking is that the max PDU size should be increased to 64 KB [I-D.ietf-idr-bgp-extended-messages] so that there is sufficient room to accommodate two signature-list blocks (i.e., one block with a current algorithm and another block with a new algorithm during transition periods) for long paths. The larger max PDU also may be required to accommodate multiple prefix announcements in an Sriram Expires January 5, 2017 [Page 18] Internet-Draft BGPSEC Design Choices July 2016 update if some optimizations such as update packing are adopted in future versions of the BGPSEC specification. It was decided that the max PDU size negotiation will be done explicitly (rather than implicitly as part of BGPSEC peering initiation). 5.3.2. Discussion It was argued that if BGPSEC negotiation included negotiation of the larger max PDU size also, then it eliminates the need for checking a new error condition (regarding max PDU size). But then it was viewed as inadvisable to have two ways of doing something (i.e., implicit in BGPSEC and also as a separate negotiation capability). It was decided that having the larger max PDU size will be a separate (explicit) capability negotiation. 5.4. Temporary Suspension of Attestations and Validations 5.4.1. Decision A BGPSEC-capable router can temporarily suspend signing and/or validation of updates during periods of route processor overload. The router should later send signed updates corresponding to the updates for which validation and signing were skipped. The router also may choose to skip only validation but still sign and forward updates during periods of congestion. 5.4.2. Discussion In some situations, a BGPSEC router may be unable to keep up with the workload of performing signing and/or validation. This can happen, for example, during BGP session recovery when a router has to send the entire routing table to a recovering router in a neighboring AS (see [CPUworkload]). So it is not mandatory that a BGPSEC router perform validation or signing of updates at all times. When the work load eases, the BGPSEC router should play catch up, sending signed updates corresponding to the updates for which validation and signing were skipped. During periods of overload, the router may simply send unsigned updates (with signatures dropped), or may sign and forward the updates with signatures (even though the router itself has not yet verified the signatures it received). 6. Incremental Deployment and Negotiation of BGPSEC Sriram Expires January 5, 2017 [Page 19] Internet-Draft BGPSEC Design Choices July 2016 6.1. Downgrade Attacks 6.1.1. Decision No attempt will be made in BGPSEC design to prevent downgrade attacks, i.e., a BGPSEC-capable router sending unsigned updates when it is capable of sending signed updates. 6.1.2. Discussion BGPSEC allows routers to temporarily suspend signing updates (see Section 5.4). Therefore, it would be contradictory if we were to try to incorporate in the BGPSEC protocol a way to detect and reject downgrade attacks. One proposed way for detecting downgrade attacks was considered, based on signed peering registrations (see Section 9.5). 6.2. Inclusion of Address Family in Capability Advertisement 6.2.1. Decision It was decided that during capability negotiation, the address family for which the BGPSEC speaker is advertising support for BGPSEC will be shared using the Address Family Identifier (AFI). Initially, two address families would be included, namely, IPv4 and IPv6. BGPSEC for use with other address families may be specified in the future. Simultaneous use of the two (i.e., IPv4 and IPv6) address families for the same BGPSEC session will require that the BGPSEC speaker must include two instances of this capability (one for each address family) in the BGPSEC OPEN message. 6.2.2. Discussion If new address families are supported in the future, they will be added in future versions of the specification. A comment was made that too many version numbers are bad for interoperability; Re- negotiation on the fly to add a new address family (i.e., without changeover to new version number) is desirable. 6.3. Incremental Deployment: Capability Negotiation 6.3.1. Decision BGPSEC will be incrementally deployable. BGPSEC routers will use capability negotiation to agree to run BGPSEC between them. If a BGPSEC router's peer does not agree to run BGPSEC, then the BGPSEC router will run only BGP-4 with that peer, i.e., it will not send BGPSEC (i.e., signed) updates to the peer. Sriram Expires January 5, 2017 [Page 20] Internet-Draft BGPSEC Design Choices July 2016 6.3.2. Discussion During partial deployment, there will be BGPSEC islands as a result of this approach to incremental deployment. Updates that originate within a BGPSEC island will generally propagate with signed AS paths to the edges of that island. As BGPsec adoption grows, the BGPsec islands will expand outward (subsuming non-BGPsec portions of the Internet) and/or pairs of islands may join together to form larger BGPsec islands. An explicit capability negotiation (outside of the BGPSEC protocol initiation) will allow for negotiating a larger max PDU size (than the current 4KB) between BGPSEC peers (see Section 5.3). 6.4. Partial Path Signing Partial path signing means that a BGPSEC AS can be permitted to sign an update that was received unsigned from a downstream neighbor. That is, the AS would add its ASN to the AS path and sign the (previously unsigned) update to other neighboring (upstream) BGPSEC ASes. It was decided that this should not be permitted. 6.4.1. Decision It was decided that partial path signing in BGPSEC will not be allowed. A BGPSEC update must be fully signed, i.e., each AS in the AS-PATH must sign the update. So in a signed update there must be a signature corresponding each AS in the AS path. 6.4.2. Discussion Partial path signing (as described above) implies that the AS path is not rigorously protected. Rigorous AS path protection is a key requirement of BGPSEC [RFC7353]. Partial path signing clearly re- introduces the following attack vulnerability: If a BGPSEC speaker can sign an unsigned update, and if signed (i.e., partially or fully signed) updates would be preferred to unsigned updates, then a faulty, misconfigured or subverted BGPSEC speaker can manufacture any unsigned update it wants (with insertion of a valid origin AS) and add a signature to it to increase the chance that its update will be preferred. 6.5. Consideration of Stub ASes with Resource Constraints: Encouraging Early Adoption Sriram Expires January 5, 2017 [Page 21] Internet-Draft BGPSEC Design Choices July 2016 6.5.1. Decision The protocol permits each pair of BGPSEC-capable ASes to negotiate BGPSEC use asymmetrically. Thus a stub AS (or downstream customer AS) can agree to perform BGPSEC only in the transmit direction and speak BGP-4 in the receive direction. In this arrangement, the ISP's (upstream) AS will not send signed updates to this stub or customer AS. Thus the stub AS can avoid the need to upgrade its route processor and RIB memory to support BGPSEC update validation. 6.5.2. Discussion Various other options were also considered for accommodating a resource-constrained stub AS as discussed below: 1. An arrangement that can be effected outside of BGPSEC specification is as follows. Through a private arrangement (invisible to other ASes), an ISP's AS (upstream AS) can truncate the stub AS (or downstream AS) from the path and sign the update as if the prefix is originating from ISP's AS (even though the update originated unsigned from the customer AS). This way the path will appear fully signed to the rest of the network. This alternative will require the owner of the prefix at the stub AS to issue a ROA for the upstream AS, so that the upstream AS is authorized to originate routes for said prefix. 2. Another type of arrangement that can also be effected outside of the BGPSEC specification is as follows. Stub AS does not sign updates but obtains an RPKI (CA) certificate, issues a router certificate under that CA certificate. It passes on the private key for the router certificate to its upstream provider. That ISP (i.e., the second hop AS) would insert a signature on behalf the stub AS using said private key obtained from the stub AS. 3. An extended ROA is created that includes the stub AS as the originator of the prefix and the upstream provider as the second hop AS, and partial signatures would be allowed (i.e., stub AS need not sign the updates). It is recognized that this approach is also authoritative and not trust based. It was observed that the extended ROA is not much different from what is done with ROA (in its current form) when a PI address is originated from a provider's AS. This approach was rejected due to possible complications with creation and use of a new RPKI object, namely, the extended ROA. Also, the validating BGPSEC router has to perform a level of indirection with approach, i.e., it has to detect if an update is not fully signed and then look for the extended ROA to validate. 4. Another method based on a different form of indirection would be as follows: Customer (stub) AS registers something like a Proxy Signer Authorization, which authorizes the second hop (i.e., Sriram Expires January 5, 2017 [Page 22] Internet-Draft BGPSEC Design Choices July 2016 provider) AS to sign on behalf of the customer AS using the provider's own key [Dynamics]. This method allows for fully signed updates (unlike the Extended ROA based approach). But this approach also requires the creation of a new RPKI object, namely, the Proxy Signer Authorization. In this approach the second hop AS has to perform a level of indirection. This approach was also rejected. The various inputs regarding ISP preferences were taken into consideration, and eventually the decision in favor of asymmetric BGPSEC was reached (Section 6.5.1). A stub AS that does asymmetric BGPSEC has the advantage that it needs to minimally upgrade to BGPSEC so it can sign updates to its upstream while it receives only unsigned updates. Thus it can avoid the cost of increased processing and memory needed to perform update validations and to store signed updates in the RIBs, respectively. 6.6. Proxy Signing 6.6.1. Decision An ISP's AS (or upstream AS) can proxy sign BGP announcements for a customer (downstream) AS provided that the customer AS obtains an RPKI (CA) certificate, issues a router certificate under that CA certificate, and it passes on the private key for that certificate to its upstream provider. That ISP (i.e., the second hop AS) would insert a signature on behalf the customer AS using the private key provided by the customer AS. This is a private arrangement between said parties and is invisible to other ASes. Thus, this arrangement is not part of the BGPSEC protocol specification BGPSEC will not make any special provisions for an ISP to use its own private key to proxy sign updates for a customer's AS. This type of proxy signing is considered a bad idea. 6.6.2. Discussion Consider a scenario when a customer's AS (say, AS8) is multi-homed to two ISPs, i.e., AS8 peers with AS1 and AS2 of ISP-1 and ISP-2, respectively. In this case AS8 would have an RPKI (CA) certificate; it issues two separate router certificates (corresponding to AS1 and AS2) under that CA certificate; and it passes on the respective private keys for those two certificates to its upstream providers AS1 and AS2. Thus AS8 has proxy signing service from both its upstream ASes. In the future, if the customer AS8 disconnects from ISP-2, then it would revoke the router certificate corresponding to AS2. Sriram Expires January 5, 2017 [Page 23] Internet-Draft BGPSEC Design Choices July 2016 6.7. Multiple Peering Sessions Between ASes 6.7.1. Decision No problems are anticipated when BGPSEC capable ASes have multiple peering sessions between them (between distinct routers). 6.7.2. Discussion As with BGP-4 ASes, BGPSEC capable ASes can also have multiple peering sessions between them. Because routers in an AS (can) have distinct private keys, the same update when propagated over these multiple peering sessions will result in multiple updates that will differ in their signatures. The peer (upstream) AS will apply its normal procedures for selecting a best path from those multiple updates (and updates from other peers). Multiple peering sessions, between different pairs of routers (between two neighboring ASes), may be simultaneously used for load sharing. This decision regarding load balancing (vs. using one peering as primary for carrying data and another as backup) is entirely local and is up to the two neighboring ASes. 7. Interaction of BGPSEC with Common BGP Features 7.1. Peer Groups In the current BGP-4, the idea of peer groups is used in BGP routers to save on processing when generating and sending updates. Multiple peers for whom the same policies apply can be organized into peer groups. A peer group can typically have tens (maybe as high as 300) of ASes in it. 7.1.1. Decision It was decided that BGPSEC updates are generated to target unique AS peers, so there is no support for peer groups in BGPSEC. 7.1.2. Discussion BGPSEC routers can use peer groups. Some of the update processing prior to forwarding to members of a peer group can be done only once per update as is done in BGP-4. Prior to forwarding the update, a BGPSEC speaker adds the peer's ASN to the data that needs to be signed and signs the update for each peer AS in the group individually. Sriram Expires January 5, 2017 [Page 24] Internet-Draft BGPSEC Design Choices July 2016 If updates were to be signed per peer group, that would require divulging information about the forward AS-set that constitutes a peer group (since the ASN of each peer would have to be included in the update). Some ISPs do not like to share this kind of information globally. 7.2. Communities The need to provide protection in BGPSEC for the community attribute was discussed. 7.2.1. Decision Community attribute(s) will not be included in what is signed in BGPSEC. 7.2.2. Discussion The community attribute - in its current definition - may be inherently defective, from a security standpoint. A substantial amount of work is needed on semantics of the community attribute, and additional work on its security aspects also needs to be done. The community attribute is not necessarily transitive; it is often used only between neighbors. In those contexts, transport security mechanisms suffice to provide integrity and authentication. (There is no need to sign data when it is passed only between peers.) It was suggested that one could include only the transitive community attributes in what is signed and propagated (across the AS path). It was noted that there is a flag available (i.e., unused) in the community attribute, and it might be used by BGPSEC (in some fashion). However, little information is available at this point about the use and function of this flag. It was speculated that potentially this flag could be used to indicate to BGPSEC if the community attribute needs protection. For now, community attributes will not be secured by BGPSEC path signatures. 7.3. Consideration of iBGP Speakers and Confederations 7.3.1. Decision An iBGP speaker that is also an eBGP speaker, and that executes BGPSEC, will necessarily carry BGPSEC data and perform eBGPSEC functions. Confederations are eBGP clouds for administrative purposes and contain multiple sub-ASs. A sub-AS is not required to sign updates sent to the main AS; only the main AS will sign and propagate BGPSEC updates to eBGPSEC peer ASes. Sriram Expires January 5, 2017 [Page 25] Internet-Draft BGPSEC Design Choices July 2016 If updates are not signed (i.e., BGPSEC is not used) within a confederation boundary, then everything will work fine at a BGPSEC speaker in the confederation that is executing BGPSEC with external peers. If updates are signed (i.e., BGPSEC is used) within a confederation boundary, then the BGPSEC speaker will be required to remove any signatures applied within the confederation, and replace them with a single signature representing the (main) AS, which will be appropriate for external BGPSEC peers. The BGPSEC specification will not specify how to perform this process. 7.3.2. Discussion This topic may need to be revisited to flesh out the details carefully. 7.4. Consideration of Route Servers in IXPs 7.4.1. Decision BGPSEC (draft-00 specification) makes no special provisions to accommodate route servers in Internet Exchange Points (IXPs) . 7.4.2. Discussion There are basically three methods that an IXP may use to propagate routes: (A) Direct bilateral peering through the IXP, (B) BGP peering between clients via a peering with a route server at the IXP (without IXP inserting its ASN in the path), and (C) BGP peering with an IXP route server, where the IXP inserts its ASN in the path. (Note: IXP's route server does not change the NEXT_HOP attribute even if it inserts its ASN in the path.) It is very rare for an IXP to use Method C because it is less attractive for the clients if their AS path length increases by one due to the IXP. A measure of the extent of use of Method A vs. Method B is given in terms of the corresponding IP traffic load percentages. As an example, at a major European IXP, these percentages are about 80% and 20% for Methods A and B, respectively. However, as the IXP grows (in terms of number of clients), it tends to migrate more towards Method B, because of the difficulties of managing up to n x (n-1)/2 direct inter- connections between n peers in Method A. To the extent an IXP is providing direct bilateral peering between clients (Method A), that model works naturally with BGPSEC. Also, if the route server in the IXP plays the role of a regular BGPSEC speaker (minus the routing part for payload) and inserts its own ASN in the path (Method C), then that model would also work well in the BGPSEC Internet and this case is trivially supported in BGPSEC. Sriram Expires January 5, 2017 [Page 26] Internet-Draft BGPSEC Design Choices July 2016 However, the draft-00 version of BGPSEC specification does not accommodate the "transparent" route server model of Method B. 7.5. Proxy Aggregation (a.k.a. AS_SETs) 7.5.1. Decision Proxy aggregation (i.e., use of AS_SETs in the AS path) will not be supported in BGPSEC. That is to say that there is no provision in BGPSEC to sign an update when an AS_SET is part of an AS path. If a BGPSEC capable router receives an update that contains an AS_SET and also finds that the update is signed, then the router will strip the signatures and interpret the update as unsigned. If the update (with AS_SET) is selected as best path, it will be forwarded unsigned. 7.5.2. Discussion Proxy aggregation does occur in the Internet today, but is it very rare. Only a very small fraction (about 0.1%) of observed updates contain AS_SETs in the AS path [ASset]. Since BGP-4 currently allows for proxy aggregation with inclusion of AS_SETs in the AS path, it is necessary that BGPSEC specify what action a receiving router must take in case such an update is received with attestation. A recently published BCP [RFC6472] recommends against the use of AS_SETs in updates, so it is anticipated that the use of AS_SETs will diminish over time. 7.6. 4-Byte AS Numbers Not all (currently deployed) BGP speakers are capable of dealing with 4-byte ASNs [RFC4893]. The standard mechanism used to accommodate such speakers requires a peer AS to translate each 4-byte ASN in a path into a reserved 2-byte ASN (AS 23456) before forwarding the update. This mechanism is incompatible with use of BGPSEC, since the ASN translation is equivalent to a route modification attack and will cause signatures corresponding to the translated 4-byte ASNs to fail validation. 7.6.1. Decision BGP speakers that are BGPSEC-capable are required to process 4-byte ASNs. 7.6.2. Discussion It is reasonable to assume that upgrades for 4-byte ASN support will be in place prior to deployment of BGPSEC. Sriram Expires January 5, 2017 [Page 27] Internet-Draft BGPSEC Design Choices July 2016 8. BGPSEC Validation 8.1. Sequence of BGPSEC Validation Processing in a Receiver It is natural to ask in what sequence a receiver must perform BGPSEC update validation so that if a failure were to occur (i.e., update was determined to be invalid) the processor would have spent the least amount of processing or other resources. 8.1.1. Decision There was agreement that the following sequence of receiver operations is quite meaningful, and are included in the initial draft-00 BGPSEC specification [I-D.lepinski-bgpsec-protocol]. However, the ordering of validation processing steps is not a normative part of the BGPSEC specification. 1. Verify that the signed update is syntactically correct. For example, check if the number of sigs match with the number of ASes in the AS path (after duly accounting for AS prepending). 2. Verify that the origin AS is authorized to advertise the prefix in question. This verification is based on data from ROAs, and does not require any crypto operations. 3. Verify that the advertisement has not yet expired. 4. Verify that the target ASN in the signature data matches the ASN of the router that is processing the advertisement. Note that the target ASN check is also a non-crypto operation and is fast. It is suggested that signature data be checked from the most recent AS to the origin. 5. Locate the public key for the router from which the advertisement was received, using the SKI from the signature data. 6. Hash the data covered by the signature algorithm. Invoke the signature validation algorithm on the following three inputs: the locally computed hash, the received signature, and the public key. There will be one output: valid or invalid. 7. Repeat steps 5 and 6 for each preceding signature in the Signature-List Block, until the signature data for the origin AS is encountered and processed, or until either of these steps fails. 8.1.2. Discussion The suggested sequence of receiver operations described above were discussed and are viewed as appropriate, if the goal is to minimize computational costs associated with cryptographic operations. One additional interesting suggestion was that when there are two Signature-List Blocks in an update, the validating router can first verify whichever of the two algorithms is cheaper to save on Sriram Expires January 5, 2017 [Page 28] Internet-Draft BGPSEC Design Choices July 2016 processing. If that Signature-List Block verifies, then the router can skip validating the other Signature- List Block. Of course, at the end of an algorithm transition period, many routers would support only the new algorithm because their old credentials would have expired. 8.2. Signing and Forwarding Updates when Signatures Failed Validation 8.2.1. Decision A BGPSEC router should sign and forward a signed update to upstream peers if it selected the update as the best path, regardless of whether the update passed or failed validation (at this router). (Note: The BGPSEC protocol specification or a companion BCP may later specify some conditions of failed update validation (TBD) under which a BGPSEC router must not select the AS path in the update.) 8.2.2. Discussion The availability of RPKI data at different routers (in the same or different ASes) may differ, depending on the sources used to acquire RPKI data. Hence an update may fail validation in one AS and the same update may pass validation in another AS. Thus an update may fail validation at one router in an AS and the same update may pass validation at another router in the same AS. A BCP may be published later in which some conditions of update failure are identified which may be unambiguous cases for rejecting the update, in which case the router must not select the AS path in the update. These cases are TBD. 8.3. Enumeration of Error Conditions Enumeration of error conditions and the recommendations for reactions to them are still under discussion. 8.3.1. Decision TBD. Also, please see Section 8.5 for the decision and discussion specifically related to syntactic errors in signatures. 8.3.2. Discussion The list here is a first cut at some possible error conditions and recommended receiver reactions in response to detection of those errors. Refinements will follow after further discussions. E1 Abnormalities that a peer (i.e., preceding AS) should definitely not have propagated to a receiving eBGPSEC router. Examples: (A) Sriram Expires January 5, 2017 [Page 29] Internet-Draft BGPSEC Design Choices July 2016 The number of signatures does not match the number of ASes in the AS path (after accounting for AS prepending); (B) There is an AS_SET in the received update and the update has signatures; (C) Other syntactic errors with sigs. Reaction: See Section 8.5. E2 Situations where a receiving eBGPSEC router can't find the cert for an AS in the AS_PATH. Reaction: Mark the update as "Invalid". It is acceptable to consider the update in best path selection. If it is chosen, then the router should sign and propagate the update. E3 Situations where a receiving eBGPSEC router can't find a ROA for the {prefix, origin} pair. Reaction: Same as in (E2) above. E4 The receiving eBGPSEC router verifies signatures and finds that the update is Invalid even though its peer might not have known (e.g., due to RPKI skew). Reaction: Same as in (E2) above. Note: Best route choice may involve choosing an unsigned update over one with "Invalid" signature(s). Hence, the signatures must not be stripped even if the update is "Invalid". No evil bit is set in the update (when it is Invalid) because an upstream peer may not get that same answer when it tries to validate. 8.4. Procedure for Processing Unsigned Updates An update may come in unsigned from an eBGP peer or internally (e.g., as an iBGP update). In the latter case, the route is possibly being originated from within the AS in consideration, or from within an AS confederation. 8.4.1. Decision If an unsigned route is received from an eBGP peer, and if it is selected, then the route will be forwarded unsigned to other eBGP peers, even BGPSEC-capable peers. If the route originated in this AS (IGP or iBGP) and is unsigned, then it should be signed and announced to external BGPSEC-capable peers. If the route originated in IGP (or iBGP) and is signed, then it was likely signed by ASes within a confederation. In this case, signatures from within the confederation would be processed and they would be deleted, and an Sriram Expires January 5, 2017 [Page 30] Internet-Draft BGPSEC Design Choices July 2016 origin AS signature will be added prior to announcement to eBGP (BGPSEC capable) peers (also see Section 7.3). 8.4.2. Discussion There is also a possibility that an update received in IGP (or iBGP) may have private ASNs in the AS path. These private ASNs would normally appear in the right most portion of the AS path. It was noted that in this case, the private ASNs to the right would be removed (as done in BGP-4 currently?), and then the update will be signed by the originating AS and announced to eBGP (BGPSEC capable) peers. 8.5. Response to Syntactic Errors in Signatures and Recommendation for Reaction Different types of error conditions were discussed in Section 8.3. Here the focus is only on syntactic error conditions in signatures. 8.5.1. Decision If there are syntactic error conditions such as (a) AS_SET and Signature-List Block both appear in an update, or (b) the number of signatures does not match the number of ASes (after accounting for any AS prepending), or (c) a parsing issue occurs with the BGPSEC_Path_Signatures attribute, then the update (with the signatures stripped) will still be considered in the best path selection algorithm. If the update is selected as the best path, then the update will be propagated unsigned. The error condition will be logged locally. A BGPSEC router will follow whatever the current IETF (IDR WG) recommendations are for notifying a peer that it is sending malformed messages. In the case when there are two Signature-List Blocks in an update, and one or more syntactic errors are found to occur within one of the Signature-List Blocks but the other Signature-List Block is free of any syntactic errors, then the update will still be considered in the best path selection algorithm after the syntactically bad Signature- List Block has been removed. If the update is selected as the best path, then the update will be propagated with only one (i.e., the error-free) Signature-List Block. The error condition will be logged locally. Sriram Expires January 5, 2017 [Page 31] Internet-Draft BGPSEC Design Choices July 2016 8.5.2. Discussion As stated above, a BGPSEC router will follow whatever the current IETF (IDR WG) recommendations are for notifying a peer that it is sending malformed messages. Question: If the error is persistent, and there is a full BGP table dump occurring, then would there be 500K such errors resulting in 500K notify messages sent to the erring peer? The answer was that rate limiting would be applied to the notify messages which should prevent any overload due to these messages. 8.6. Enumeration of Validation States Various validation conditions (i.e., situations) are possible which can be mapped to validation states for possible input to BGPSEC decision process. These conditions can be related to whether or not an update is signed, Expire Time checked, AS origin validation checked against a ROA, signatures verification passed, etc. 8.6.1. Decision It was decided that BGPSEC validation outcomes will be mapped to one of only two validation states: (1) Valid - passed all validation checks (i.e., Expire Time check, prefix-origin and Signature-List Block validation), and (2) Invalid - all other possibilities. It was decided subsequently that the terms "Valid" and "Invalid" will be generally not used in the context of update validation in BGPSEC. Instead the terms "Verified" and "Unverified" will be used. The term "Verified" would connote the same as "Valid" described above. The term "Unverified" would include all other situations such as (1) unverified due to lack of or insufficient RPKI data, (2) signature Expire-Time check failed, (3) prefix-origin validation failed, (4) signature checks were performed and one or more of them failed, (5) insufficient resources to process the signature blocks at this time, etc. The text in this document will be modified at a future date to consistently reflect this decision regarding the terminology change. For now we would continue to use the terms "Valid" and "Invalid" in the document. 8.6.2. Discussion It may be noted that the result of update validation is just an additional input for the BGP decision process. The router configuration ultimately has control over what action (regarding BGP path selection) is taken. Sriram Expires January 5, 2017 [Page 32] Internet-Draft BGPSEC Design Choices July 2016 Initially, four validation states were considered: (1) Update is not signed; (2) Update is signed but router does not have corresponding RPKI data to perform validation check; (3) Invalid (validation check performed and failed); (4) Valid (validation check performed and passed). Later, it was decided that BGPSEC validation outcomes will be mapped to one of only two validation states as stated above. It was observed that an update can be invalid for many different reasons. To begin to differentiate these numerous reasons and to try to enumerate different flavors of the Invalid state is not likely to be constructive in route selection decision, and may even introduce to new vulnerability in the system. However, some questions remain such as the following. Question: Is there a need to define a separate validation state for the case when update is not signed but {prefix, origin} pair matched with ROA information? This question was discussed, and a tentative conclusion was that this is in principle similar to validation based on partial signatures and that was ruled out earlier. So there is no need to add another validation state for this case; treat it as "Unverified" (i.e., "Invalid"). Questions still remain, e.g., would the relying party want to give said update a higher preference over another unsigned update that failed ROA validation or over a signed update that failed both signature and ROA validation? 8.7. Mechanism for Transporting Validation State through iBGP 8.7.1. Decision BGPSEC validation need be performed only at eBGP edges. The validation status of a BGP signed/unsigned update may be conveyed via iBGP from an ingress edge router to an egress edge router. Local policy in the AS will determine the means by which the validation status is conveyed internally, using various pre-existing mechanisms, e.g., setting a BGP community, or modifying a metric value such as Local_Pref or MED. A signed update that cannot be validated (except those with syntax errors) should be forwarded with signatures from the ingress to the egress router, where it is signed when propagated towards other eBGPSEC speakers in neighboring ASs. Based entirely on local policy settings, an egress router may trust the validation status conveyed by an ingress router or it may perform its own validation. The latter approach may be used at an operator's discretion, under circumstances when RPKI skew is known to happen at different routers within an AS. Sriram Expires January 5, 2017 [Page 33] Internet-Draft BGPSEC Design Choices July 2016 8.7.2. Discussion The attribute used to represent the validation state can be carried between ASes if desired. ISPs may like to carry it over their eBGP links between their own ASes (e.g., AS701, AS702). A peer (or customer) may receive it over an eBGP link from a provider, and may want to use it to shortcut their own validation check. However, the peer (or customer) should be aware that this validation-state attribute is just a preview of a neighbor's validation and must perform their own validation check in order to be sure of the actual state of update's validation. Question: Should validation state propagation be protected by attestation in case it has utility for diagnostics purposes? It was decided not to protect the validation state information using signatures. The following are meant to be only as suggestions for the AS operator; none of what follows is part of the BGPSEC specification as such. The following Validation states may be needed for propagation via iBGP between edge routers in an AS: o Validation states communicated in iBGP for an unsigned update (Origin validation result): (1) Valid, (2) Invalid, (3) Unknown, (4) Validation Deferred. * An update could be unsigned for two reasons but they need not be distinguished: (a) Because it had no signatures (came in unsigned from an eBGP peer), or (b) Signatures were present but stripped due to syntax errors. o Validation states communicated in iBGP for a Signed update: (1) Valid, (2) Invalid, (3) Validation Deferred. The reason for conveying the additional "Validation Deferred" state may be stated as follows. An ingress edge Router A receiving an update from an eBGPSEC peer may not attempt to validate signatures (e.g., in a processor overload situation), and in that case Router A should convey "Validation Deferred" state for that signed update (if selected for best path) in iBGP to other edge routers. Then an egress edge Router B upon receiving the update from ingress Router A would be able to perform its own validation (origin validation for unsigned or signature validation for signed update). As stated before, the egress Router B always may choose to perform its own validation when it receives an update from iBGP (independent of the validation status conveyed in iBGP) to account for the possibility of RPKI data skew at different routers. These various choices are local and entirely up to operator discretion. Sriram Expires January 5, 2017 [Page 34] Internet-Draft BGPSEC Design Choices July 2016 9. Operational Considerations 9.1. Interworking with BGP Graceful Restart BGP Graceful Restart (BGP-GR) [RFC4724] is a mechanism currently used to facilitate non-stop packet forwarding when the control plane is recovering from a fault (i.e., BGP session is restarted), but the data plane is functioning. A question was asked regarding if there are any special concerns about how BGP-GR works while BGPSEC is operational? Also, what happens if the BGP router operation transitions from BGP-4 to BGP-GR to BGPSEC, in that order? 9.1.1. Decision No decision was made relative to this issue. 9.1.2. Discussion BGP-GR can be implemented with BGPSEC just as it is currently implemented with BGP-4. The Restart State bit, Forwarding State bit, End-of-RIB marker, Staleness marker (in RIB-in), and Selection_Deferral_Timer are key parameters associated with BGP-GR [RFC4724]. These parameters would need to be incorporated into the BGPSEC session negotiation and/or operation just as the routers do now with the current BGP-4. Regarding what happens if the BGP router transitions from BGP-4 to BGP-GR to BGPSEC, the answer would simply be as follows. If there is software upgrade from BGP-4 to BGPSEC during BGP-GR (assuming upgrade is being done on a live BGP speaker), then the BGP-GR session would (should) be terminated before a BGPSEC session is initiated. Once the eBGPSEC peering session is established, then the receiving eBGPSEC speaker will see signed updates from the sending (newly upgraded) eBGPSEC speaker. There is no apparent harm (it may, in fact, be desirable) if the receiving speaker continues to use previously-learned BGP-4 routes from the sending speaker until they are replaced by new BGPSEC routes. However, if the Forwarding State bit is set to zero by the sending speaker (i.e., the newly upgraded speaker) during BGPSEC session negotiation, then the receiving speaker would mark all previously-learned BGP-4 routes from that sending speaker as "Stale" in its RIB-in. Then, as fresh BGPSEC updates (possibly mixed with some unsigned BGP-4 updates) come in, the "Stale" routes will be replaced or refreshed. Sriram Expires January 5, 2017 [Page 35] Internet-Draft BGPSEC Design Choices July 2016 9.2. BCP Recommendations for Minimizing Churn: Certificate Expiry/ Revocation and Signature Expire Time 9.2.1. Decision This is still work in progress. 9.2.2. Discussion BCP recommendations for minimizing churn in BGPSEC have been discussed. There are potentially various strategies on how routers should react in the events of certificate expiry/revocation and signature Expire Time exhaustion [Dynamics]. The details will be documented in the near future after additional work is completed. 9.3. Outsourcing Update Validation 9.3.1. Decision Update signature validation and signing can be outsourced to an off- board server or processor. 9.3.2. Discussion Possibly an off-router box (one or more per AS) can be used that performs path validation. For example, these capabilities might be incorporated into a route reflector. At ingress, one needs the RIB- in entries validated; not the RIB-out entries. So the off-router box is probably unlike the traditional route reflector; it sits at net edge and validates all incoming BGPSEC updates. Thus it appears that each router passes each BGPSEC update it receives to the off-router box and receives a validation result before it stores the route in the RIB-in. Question: What about failure modes here? They would be dependent on (1) How much of the control plane is outsourced; (2) Reliability of the off-router box (or, equivalently communication to it); and (3) How centralized vs. distributed is this arrangement? When any kind of outsourcing is done, the user needs to be watchful and ensure that the outsourcing does not cross trust/security boundaries. 9.4. New Hardware Capability 9.4.1. Decision It is assumed that BGPSEC routers (PE routers and route reflectors) will have significantly upgraded hardware - much more memory for RIBs and hardware crypto assistance. However, stub ASes would not need to make such upgrades because they can negotiate asymmetric BGPSEC Sriram Expires January 5, 2017 [Page 36] Internet-Draft BGPSEC Design Choices July 2016 capability with their upstream ASes, i.e., they sign updates to the upstream AS but receive only BGP-4 (unsigned) updates (see Section 6.5). 9.4.2. Discussion It is accepted that it might take several years to go beyond test deployment, because of the need for additional memory and processing capability. However, because BGPSEC deployment will be incremental, and because signed updates are not sent outside of a set of contiguous BGPSEC-enabled ASes, it is not clear how much additional (RIB) memory will be required during initial deployment. See (see [RIB_size]) for preliminary results on modeling and estimation of BGPSEC RIB size and its projected growth. Hardware cryptographic support reduces the computation burden on the route processor, and offers good security for router private keys. However, given the incremental deployment model, it also is not clear how substantial a cryptographic processing load will be incurred, initially. 9.5. Signed Peering Registrations 9.5.1. Decision The idea of signed BGP peering registrations (for the purpose of path validation) was rejected. 9.5.2. Discussion The idea of using a secure map of AS relationships to "validate" updates was discussed and rejected. The reason for not pursuing such solutions was that they can't provide strong guarantees about the validity of updates. Using these techniques, one can say only that an update is 'plausible', but cannot say it is 'definitely' valid (based on signed peering relations alone). 10. Co-authors Rob Austein sra@hactrn.net Internet Systems Consortium Steven Bellovin smb@cs.columbia.edu Columbia University Randy Bush randy@psg.com Internet Initiative Japan, Inc. Russ Housley housley@vigilsec.com Vigil Security Sriram Expires January 5, 2017 [Page 37] Internet-Draft BGPSEC Design Choices July 2016 Stephen Kent kent@bbn.com BBN Technologies Warren Kumari warren@kumari.net Google Matt Lepinski mlepinski@ncf.edu New College of Florida Doug Montgomery dougm@nist.gov USA NIST Kotikalapudi Sriram ksriram@nist.gov USA NIST Samuel Weiler weiler@watson.org Cobham 11. Acknowledgements The authors would like to thank John Scudder, Ed Kern, Pradosh Mohapatra, Keyur Patel, David Ward, Rudiger Volk, Heather Schiller, Jason Schiller, Chris Morrow, Sandy Murphy, Russ Mundy, Mark Reynolds, Sean Turner, Sharon Goldberg, Chris Hall, Shane Amante, Luke Berndt, and Doug Maughan for their valuable input and review. 12. IANA Considerations This memo includes no request to IANA. 13. Security Considerations This memo requires no security considerations. See [I-D.ietf-sidr-bgpsec-protocol] for security considerations for the BGPSEC protocol. 14. References 14.1. Normative References [I-D.lepinski-bgpsec-protocol] Lepinski, M., "BGPSEC Protocol Specification", draft- lepinski-bgpsec-protocol-00 (work in progress), March 2011. Sriram Expires January 5, 2017 [Page 38] Internet-Draft BGPSEC Design Choices July 2016 [RFC3779] Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP Addresses and AS Identifiers", RFC 3779, DOI 10.17487/RFC3779, June 2004, . [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, DOI 10.17487/RFC4271, January 2006, . [RFC4893] Vohra, Q. and E. Chen, "BGP Support for Four-octet AS Number Space", RFC 4893, DOI 10.17487/RFC4893, May 2007, . [RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70, RFC 5652, DOI 10.17487/RFC5652, September 2009, . [RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms for DNS (EDNS(0))", STD 75, RFC 6891, DOI 10.17487/RFC6891, April 2013, . 14.2. Informative References [ASset] Sriram, K. and D. Montgomery, "Measurement Data on AS_SET and AGGREGATOR: Implications for {Prefix, Origin} Validation Algorithms", IETF SIDR WG presentation, IETF 78, July 2010, . [CiscoIOS] "Cisco IOS RFD implementation", . [CPUworkload] Sriram, K. and R. Bush, "Estimating CPU Cost of BGPSEC on a Router", Presented at RIPE-63; also at IETF-83 SIDR WG Meeting, March 2012, . [Dynamics] Sriram, K. and et al., "Potential Impact of BGPSEC Mechanisms on Global BGP Dynamics", December 2009, . Sriram Expires January 5, 2017 [Page 39] Internet-Draft BGPSEC Design Choices July 2016 [I-D.draft-clynn-s-bgp] Lynn, C., Mukkelson, J., and K. Seo, "Secure BGP (S-BGP)", June 2003, . [I-D.ietf-idr-bgp-extended-messages] Bush, R., Patel, K., and D. Ward, "Extended Message support for BGP", draft-ietf-idr-bgp-extended-messages-13 (work in progress), June 2016. [I-D.ietf-sidr-bgpsec-overview] Lepinski, M. and S. Turner, "An Overview of BGPsec", draft-ietf-sidr-bgpsec-overview-08 (work in progress), June 2016. [I-D.ietf-sidr-bgpsec-protocol] Lepinski, M. and K. Sriram, "BGPsec Protocol Specification", draft-ietf-sidr-bgpsec-protocol-17 (work in progress), June 2016. [JunOS] "Juniper JunOS RFD implementation", . [Mao02] Mao, Z. and et al., "Route-flap Damping Exacerbates Internet Routing Convergence", August 2002, . [RFC2439] Villamizar, C., Chandra, R., and R. Govindan, "BGP Route Flap Damping", RFC 2439, DOI 10.17487/RFC2439, November 1998, . [RFC4055] Schaad, J., Kaliski, B., and R. Housley, "Additional Algorithms and Identifiers for RSA Cryptography for use in the Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 4055, DOI 10.17487/RFC4055, June 2005, . [RFC4724] Sangli, S., Chen, E., Fernando, R., Scudder, J., and Y. Rekhter, "Graceful Restart Mechanism for BGP", RFC 4724, DOI 10.17487/RFC4724, January 2007, . Sriram Expires January 5, 2017 [Page 40] Internet-Draft BGPSEC Design Choices July 2016 [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, . [RFC5396] Huston, G. and G. Michaelson, "Textual Representation of Autonomous System (AS) Numbers", RFC 5396, DOI 10.17487/RFC5396, December 2008, . [RFC6090] McGrew, D., Igoe, K., and M. Salter, "Fundamental Elliptic Curve Cryptography Algorithms", RFC 6090, DOI 10.17487/RFC6090, February 2011, . [RFC6472] Kumari, W. and K. Sriram, "Recommendation for Not Using AS_SET and AS_CONFED_SET in BGP", BCP 172, RFC 6472, DOI 10.17487/RFC6472, December 2011, . [RFC6480] Lepinski, M. and S. Kent, "An Infrastructure to Support Secure Internet Routing", RFC 6480, DOI 10.17487/RFC6480, February 2012, . [RFC6482] Lepinski, M., Kent, S., and D. Kong, "A Profile for Route Origin Authorizations (ROAs)", RFC 6482, DOI 10.17487/RFC6482, February 2012, . [RFC6483] Huston, G. and G. Michaelson, "Validation of Route Origination Using the Resource Certificate Public Key Infrastructure (PKI) and Route Origin Authorizations (ROAs)", RFC 6483, DOI 10.17487/RFC6483, February 2012, . [RFC6487] Huston, G., Michaelson, G., and R. Loomans, "A Profile for X.509 PKIX Resource Certificates", RFC 6487, DOI 10.17487/RFC6487, February 2012, . [RFC6811] Mohapatra, P., Scudder, J., Ward, D., Bush, R., and R. Austein, "BGP Prefix Origin Validation", RFC 6811, DOI 10.17487/RFC6811, January 2013, . Sriram Expires January 5, 2017 [Page 41] Internet-Draft BGPSEC Design Choices July 2016 [RFC7132] Kent, S. and A. Chi, "Threat Model for BGP Path Security", RFC 7132, DOI 10.17487/RFC7132, February 2014, . [RFC7353] Bellovin, S., Bush, R., and D. Ward, "Security Requirements for BGP Path Validation", RFC 7353, DOI 10.17487/RFC7353, August 2014, . [RIB_size] Sriram, K. and et al., "RIB Size Estimation for BGPSEC", June 2011, . [RIPE580] Bush, R. and et al., "RIPE-580: RIPE Routing Working Group Recommendations on Route-flap Damping", January 2013, . Author's Address Kotikalapudi Sriram (editor) USA NIST 100 Bureau Drive Gaithersburg, MD 20899 USA Email: ksriram@nist.gov Sriram Expires January 5, 2017 [Page 42]