Internet Engineering Task Force E. Chen, Ed. Internet-Draft Cisco Systems, Inc. Updates: 1997, 4271, 4360, 4456, 4760, J. Scudder, Ed. 5543, 5701, 6368, 6790 (if Juniper Networks approved) P. Mohapatra Intended status: Standards Track Sproute Networks Expires: December 15, 2014 K. Patel Cisco Systems, Inc. June 13, 2014 Revised Error Handling for BGP UPDATE Messages draft-ietf-idr-error-handling-13 Abstract According to the base BGP specification, a BGP speaker that receives an UPDATE message containing a malformed attribute is required to reset the session over which the offending attribute was received. This behavior is undesirable as a session reset would impact not only routes with the offending attribute, but also other valid routes exchanged over the session. This document partially revises the error handling for UPDATE messages, and provides guidelines for the authors of documents defining new attributes. Finally, it revises the error handling procedures for a number of existing attributes. This document updates error handling for RFCs 1997, 4271, 4360, 4456, 4760, 5543, 5701, 6368 and 6790. 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 December 15, 2014. Chen, et al. Expires December 15, 2014 [Page 1] Internet-Draft Revised Error Handling for BGP June 2014 Copyright Notice Copyright (c) 2014 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 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. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4 2. Error-Handling Approaches . . . . . . . . . . . . . . . . . . 4 3. Revision to BGP UPDATE Message Error Handling . . . . . . . . 4 4. Attribute Length Fields . . . . . . . . . . . . . . . . . . . 6 5. Parsing of NLRI Fields . . . . . . . . . . . . . . . . . . . 7 5.1. Encoding NLRI . . . . . . . . . . . . . . . . . . . . . . 7 5.2. Missing NLRI . . . . . . . . . . . . . . . . . . . . . . 7 5.3. Syntactic Correctness of NLRI Fields . . . . . . . . . . 8 5.4. Typed NLRI . . . . . . . . . . . . . . . . . . . . . . . 8 6. Operational Considerations . . . . . . . . . . . . . . . . . 9 7. Error Handling Procedures for Existing Attributes . . . . . . 10 7.1. ORIGIN . . . . . . . . . . . . . . . . . . . . . . . . . 10 7.2. AS_PATH . . . . . . . . . . . . . . . . . . . . . . . . . 10 7.3. NEXT_HOP . . . . . . . . . . . . . . . . . . . . . . . . 11 7.4. MULTI_EXIT_DISC . . . . . . . . . . . . . . . . . . . . . 11 7.5. LOCAL_PREF . . . . . . . . . . . . . . . . . . . . . . . 11 7.6. ATOMIC_AGGREGATE . . . . . . . . . . . . . . . . . . . . 12 7.7. AGGREGATOR . . . . . . . . . . . . . . . . . . . . . . . 12 Chen, et al. Expires December 15, 2014 [Page 2] Internet-Draft Revised Error Handling for BGP June 2014 7.8. Community . . . . . . . . . . . . . . . . . . . . . . . . 12 7.9. ORIGINATOR_ID . . . . . . . . . . . . . . . . . . . . . . 12 7.10. CLUSTER_LIST . . . . . . . . . . . . . . . . . . . . . . 13 7.11. MP_REACH_NLRI . . . . . . . . . . . . . . . . . . . . . . 13 7.12. MP_UNREACH_NLRI . . . . . . . . . . . . . . . . . . . . . 14 7.13. Traffic Engineering path attribute . . . . . . . . . . . 14 7.14. Extended Community . . . . . . . . . . . . . . . . . . . 14 7.15. IPv6 Address Specific BGP Extended Community Attribute . 14 7.16. BGP Entropy Label Capability Attribute . . . . . . . . . 15 7.17. ATTR_SET . . . . . . . . . . . . . . . . . . . . . . . . 15 8. Guidance for Authors of BGP Specifications . . . . . . . . . 15 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 10. Security Considerations . . . . . . . . . . . . . . . . . . . 16 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 16 12.1. Normative References . . . . . . . . . . . . . . . . . . 16 12.2. Informative References . . . . . . . . . . . . . . . . . 18 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18 1. Introduction According to the base BGP specification [RFC4271], a BGP speaker that receives an UPDATE message containing a malformed attribute is required to reset the session over which the offending attribute was received. This behavior is undesirable as a session reset would impact not only routes with the offending attribute, but also other valid routes exchanged over the session. In the case of optional transitive attributes, the behavior is especially troublesome and may present a potential security vulnerability. The reason is that such attributes may have been propagated without being checked by intermediate routers that do not recognize the attributes -- in effect the attribute may have been tunneled, and when they do reach a router that recognizes and checks them, the session that is reset may not be associated with the router that is at fault. To make matters worse, in such cases although the problematic attributes may have originated with a single update transmitted by a single BGP speaker, by the time they encounter a router that checks them they may have been replicated many times, and thus may cause the reset of many peering sessions. Thus the damage inflicted may be multiplied manyfold. The goal for revising the error handling for UPDATE messages is to minimize the impact on routing by a malformed UPDATE message, while maintaining protocol correctness to the extent possible. This can be achieved largely by maintaining the established session and keeping the valid routes exchanged, but removing the routes carried in the malformed UPDATE from the routing system. Chen, et al. Expires December 15, 2014 [Page 3] Internet-Draft Revised Error Handling for BGP June 2014 This document partially revises the error handling for UPDATE messages, and provides guidelines for the authors of documents defining new attributes. Finally, it revises the error handling procedures for a number of existing attributes. Specifically, the error handling procedures of [RFC1997], [RFC4271], [RFC4360], [RFC4456], [RFC4760], [RFC5543], [RFC5701], [RFC6368] and [RFC6790] are revised. 1.1. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. 2. Error-Handling Approaches In this document we refer to four different approaches to handling errors found in BGP path attributes. They are as follows (listed in order, from the one with the "strongest" action to the one with the "weakest" action): o Session reset: This is the approach used throughout the base BGP specification [RFC4271], where a NOTIFICATION is sent and the session terminated. o AFI/SAFI disable: [RFC4760] specifies a procedure for disabling a particular AFI/SAFI. o Treat-as-withdraw: In this approach, the UPDATE message containing the path attribute in question MUST be treated as though all contained routes had been withdrawn just as if they had been listed in the WITHDRAWN ROUTES field (or in the MP_UNREACH_NLRI attribute if appropriate) of the UPDATE message, thus causing them to be removed from the Adj-RIB-In according to the procedures of [RFC4271]. o Attribute discard: In this approach the malformed attribute MUST be discarded and the UPDATE message continues to be processed. This approach must not be used except in the case of an attribute that has no effect on route selection or installation. 3. Revision to BGP UPDATE Message Error Handling This specification amends [RFC4271] Section 6.3 in a number of ways. See also Section 7 for treatment of specific path attributes. a. The first paragraph is revised as follows: Chen, et al. Expires December 15, 2014 [Page 4] Internet-Draft Revised Error Handling for BGP June 2014 Old Text: All errors detected while processing the UPDATE message MUST be indicated by sending the NOTIFICATION message with the Error Code UPDATE Message Error. The error subcode elaborates on the specific nature of the error. New Text: An error detected while processing the UPDATE message for which a session reset is specified MUST be indicated by sending the NOTIFICATION message with the Error Code UPDATE Message Error. The error subcode elaborates on the specific nature of the error. b. Error handling for the following case remains unchanged: If the Withdrawn Routes Length or Total Attribute Length is too large (i.e., if Withdrawn Routes Length + Total Attribute Length + 23 exceeds the message Length), then the Error Subcode MUST be set to Malformed Attribute List. c. Attribute Flag error handling is revised as follows: Old Text: If any recognized attribute has Attribute Flags that conflict with the Attribute Type Code, then the Error Subcode MUST be set to Attribute Flags Error. The Data field MUST contain the erroneous attribute (type, length, and value). New Text: If the value of either the Optional or Transitive bits in the Attribute Flags is in conflict with their specified values, then the attribute MUST be treated as malformed and the treat-as-withdraw approach used, unless the specification for the attribute mandates different handling for incorrect Attribute Flags. d. If any of the well-known mandatory attributes are not present in an UPDATE message, then "treat-as-withdraw" MUST be used. (Note that [RFC4760] reclassifies NEXT_HOP as what is effectively discretionary.) Chen, et al. Expires December 15, 2014 [Page 5] Internet-Draft Revised Error Handling for BGP June 2014 e. "Treat-as-withdraw" MUST be used for the cases that specify a session reset and involve any of the attributes ORIGIN, AS_PATH, NEXT_HOP, MULTI_EXIT_DISC, or LOCAL_PREF. f. "Attribute discard" MUST be used for any of the cases that specify a session reset and involve ATOMIC_AGGREGATE or AGGREGATOR. g. If the MP_REACH_NLRI attribute or the MP_UNREACH_NLRI [RFC4760] attribute appears more than once in the UPDATE message, then a NOTIFICATION message MUST be sent with the Error Subcode "Malformed Attribute List". If any other attribute (whether recognized or unrecognized) appears more than once in an UPDATE message, then all the occurrences of the attribute other than the first one SHALL be discarded and the UPDATE message continue to be processed. h. When multiple attribute errors exist in an UPDATE message, if the same approach (either "session reset", "treat-as-withdraw" or "attribute discard") is specified for the handling of these malformed attributes, then the specified approach MUST be used. Otherwise the approach with the strongest action MUST be used. i. The Withdrawn Routes field MUST be checked for syntactic correctness in the same manner as the NLRI field. This is discussed further below, and in Section 5.3. j. Finally, we observe that in order to use the approach of "treat- as-withdraw", the entire NLRI field and/or the MP_REACH_NLRI and MP_UNREACH_NLRI attributes need to be successfully parsed -- what this entails is discussed in more detail in Section 5. If this is not possible, the procedures of [RFC4271] and/or [RFC4760] continue to apply, meaning that the "session reset" approach (or the "AFI/SAFI disable" approach) MUST be followed. 4. Attribute Length Fields There are two error cases in which the Total Attribute Length value can be in conflict with the enclosed path attributes, which themselves carry length values. In the "overrun" case, as the enclosed path attributes are parsed, the length of the last encountered path attribute would cause the Total Attribute Length to be exceeded. In the "underrun" case, as the enclosed path attributes are parsed, after the last successfully-parsed attribute, fewer than three octets remain, or fewer than four octets, if the Attribute Flags field has the Extended Length bit set -- that is, there remains unconsumed data in the path attributes but yet insufficient data to encode a single minimum-sized path attribute. In either of these Chen, et al. Expires December 15, 2014 [Page 6] Internet-Draft Revised Error Handling for BGP June 2014 cases an error condition exists and the treat-as-withdraw approach MUST be used (unless some other, more severe error is encountered dictating a stronger approach), and the Total Attribute Length MUST be relied upon to enable the beginning of the NLRI field to be located. For all path attributes other than those specified as having an attribute length that may be zero it SHALL be considered a syntax error for the attribute to have a length of zero. (Of the path attributes considered in this specification, only AS_PATH and ATOMIC_AGGREGATE may validly have an attribute length of zero.) 5. Parsing of NLRI Fields 5.1. Encoding NLRI To facilitate the determination of the NLRI field in an UPDATE with a malformed attribute: o The MP_REACH_NLRI or MP_UNREACH_NLRI attribute (if present) SHALL be encoded as the very first path attribute in an UPDATE. o An UPDATE message MUST NOT contain more than one of the following: non-empty Withdrawn Routes field, non-empty Network Layer Reachability Information field, MP_REACH_NLRI attribute, and MP_UNREACH_NLRI attribute. Since older BGP speakers may not implement these restrictions, an implementation MUST still be prepared to receive these fields in any position or combination. If the encoding of [RFC4271] is used, the NLRI field for the IPv4 unicast address family is carried immediately following all the attributes in an UPDATE. When such an UPDATE is received, we observe that the NLRI field can be determined using the "Message Length", "Withdrawn Route Length" and "Total Attribute Length" (when they are consistent) carried in the message instead of relying on the length of individual attributes in the message. 5.2. Missing NLRI [RFC4724] specifies an End-of-RIB message ("EoR") that can be encoded as an UPDATE message that contains only a MP_UNREACH_NLRI attribute that encodes no NLRI (it can also be a completely empty UPDATE message in the case of the "legacy" encoding). In all other well- specified cases, an UPDATE either carries only withdrawn routes (either in the Withdrawn Routes field, or the MP_UNREACH_NLRI attribute), or it advertises reachable routes (either in the Network Chen, et al. Expires December 15, 2014 [Page 7] Internet-Draft Revised Error Handling for BGP June 2014 Layer Reachability Information field, or the MP_REACH_NLRI attribute). Thus, if an UPDATE message is encountered that does contain path attributes other than MP_UNREACH_NLRI and doesn't encode any reachable NLRI, we cannot be confident that the NLRI have been successfully parsed as Section 3 (j) requires. For this reason, if any path attribute errors are encountered in such an UPDATE message, and if any encountered error specifies an error-handling approach other than "attribute discard", then the "session reset" approach MUST be used. 5.3. Syntactic Correctness of NLRI Fields The NLRI field or Withdrawn Routes field SHALL be considered "syntactically incorrect" if either of the following are true: o The length of any of the included NLRI is greater than 32, o When parsing NLRI contained in the field, the length of the last NLRI found exceeds the amount of unconsumed data remaining in the field. Similarly, the MP_REACH_NLRI or MP_UNREACH_NLRI attribute of an update SHALL be considered to be incorrect if any of the following are true: o The length of any of the included NLRI is inconsistent with the given AFI/SAFI (for example, if an IPv4 NLRI has a length greater than 32 or an IPv6 NLRI has a length greater than 128), o When parsing NLRI contained in the attribute, the length of the last NLRI found exceeds the amount of unconsumed data remaining in the attribute. o The attribute flags of the attribute are inconsistent with those specified in [RFC4760]. o The length of the MP_UNREACH_NLRI attribute is less than 3, or the length of the MP_REACH_NLRI attribute is less than 5. 5.4. Typed NLRI Certain address families, for example MCAST-VPN [RFC6514], MCAST-VPLS [RFC7117] and EVPN [I-D.ietf-l2vpn-evpn] have NLRI that are typed. Since supported type values within the address family are not expressed in the MP-BGP capability [RFC4760], it is possible for a BGP speaker to advertise support for the given address family and Chen, et al. Expires December 15, 2014 [Page 8] Internet-Draft Revised Error Handling for BGP June 2014 sub-address family while still not supporting a particular type of NLRI within that AFI/SAFI. A BGP speaker advertising support for such a typed address family MUST handle routes with unrecognized NLRI types within that address family by discarding them, unless the relevant specification for that address family specifies otherwise. 6. Operational Considerations Although the "treat-as-withdraw" error-handling behavior defined in Section 2 makes every effort to preserve BGP's correctness, we note that if an UPDATE received on an IBGP session is subjected to this treatment, inconsistent routing within the affected Autonomous System may result. The consequences of inconsistent routing can include long-lived forwarding loops and black holes. While lamentable, this issue is expected to be rare in practice, and more importantly is seen as less problematic than the session-reset behavior it replaces. When a malformed attribute is indeed detected over an IBGP session, we RECOMMEND that routes with the malformed attribute be identified and traced back to the ingress router in the network where the routes were sourced or received externally, and then a filter be applied on the ingress router to prevent the routes from being sourced or received. This will help maintain routing consistency in the network. Even if inconsistent routing does not arise, the "treat-as-withdraw" behavior can cause either complete unreachability or sub-optimal routing for the destinations whose routes are carried in the affected UPDATE message. Note that "treat-as-withdraw" is different from discarding an UPDATE message. The latter violates the basic BGP principle of incremental update, and could cause invalid routes to be kept. Because of these potential issues, a BGP speaker MUST provide debugging facilities to permit issues caused by a malformed attribute to be diagnosed. At a minimum, such facilities MUST include logging an error listing the NLRI involved, and containing the entire malformed UPDATE message when such an attribute is detected. The malformed UPDATE message SHOULD be analyzed, and the root cause SHOULD be investigated. Chen, et al. Expires December 15, 2014 [Page 9] Internet-Draft Revised Error Handling for BGP June 2014 7. Error Handling Procedures for Existing Attributes In the following subsections, we elaborate on the conditions for error-checking various path attributes, and specify what approach(es) should be used to handle malformations. It is possible that implementations may apply other error checks not contemplated here. If so, the error handling approach given here should generally be applied. This section addresses all path attributes that are defined at the time of this writing, that were not defined with error-handling consistent with Section 8, and that are not marked as "deprecated" in [IANA-BGP-ATTRS]. Attributes 17 (AS4_PATH), 18 (AS4_AGGREGATOR), 22 (PMSI_TUNNEL), 23 (Tunnel Encapsulation Attribute), 26 (AIGP), 27 (PE Distinguisher Labels) and 29 (BGP-LS Attribute) do have error- handling consistent with Section 8 and thus are not further discussed herein. Attributes 11 (DPA), 12 (ADVERTISER), 13 (RCID_PATH / CLUSTER_ID), 19 (SAFI Specific Attribute), 20 (Connector Attribute) and 21 (AS_PATHLIMIT) are deprecated and thus are not further discussed herein. 7.1. ORIGIN The attribute is considered malformed if its length is not 1, or it has an undefined value [RFC4271]. An UPDATE message with a malformed ORIGIN attribute SHALL be handled using the approach of "treat-as-withdraw". 7.2. AS_PATH An AS_PATH is considered malformed if an unrecognized segment type is encountered, or if it contains a malformed segment. A segment is considered malformed if any of the following obtains: o There is an overrun, where the path segment length field of the last segment encountered would cause the Attribute Length to be exceeded. o There is an underrun, where after the last successfully-parsed segment, there is only a single octet remaining (that is, there is not enough unconsumed data to provide even an empty segment header). o It has a path segment length field of zero. An UPDATE message with a malformed AS_PATH attribute SHALL be handled using the approach of "treat-as-withdraw". Chen, et al. Expires December 15, 2014 [Page 10] Internet-Draft Revised Error Handling for BGP June 2014 [RFC4271] also says that an implementation optionally "MAY check whether the leftmost ... AS in the AS_PATH attribute is equal to the autonomous system number of the peer that sent the message". A BGP implementation SHOULD also handle routes that violate this check using "treat-as-withdraw", but MAY follow the session reset behavior if configured to do so. 7.3. NEXT_HOP According to [RFC4271] the attribute is considered malformed if it is syntactically incorrect. To quote from that document, "Syntactic correctness means that the NEXT_HOP attribute represents a valid IP host address", but it does not go on to define what it means to be a "valid IP host address". Therefore: An IP host address SHOULD be considered invalid if it appears in the "IANA IPv4 Special-Purpose Address Registry" [IANA-IPV4] and either the "destination" or the "forwardable" boolean in that registry is given as "false". An implementation SHOULD provide a means to modify the list of invalid host addresses by configuration -- these are sometimes referred to as "Martians". An UPDATE message with a malformed NEXT_HOP attribute SHALL be handled using the approach of "treat-as-withdraw". 7.4. MULTI_EXIT_DISC The attribute is considered malformed if its length is not 4 [RFC4271]. An UPDATE message with a malformed MULTI_EXIT_DISC attribute SHALL be handled using the approach of "treat-as-withdraw". 7.5. LOCAL_PREF The error handling of [RFC4271] is revised as follows. o If the LOCAL_PREF attribute is received from an external neighbor, it SHALL be discarded using the approach of "attribute discard", or o if received from an internal neighbor, it SHALL be considered malformed if its length is not equal to 4. If malformed, the UPDATE SHALL be handled using the approach of "treat-as-withdraw". Chen, et al. Expires December 15, 2014 [Page 11] Internet-Draft Revised Error Handling for BGP June 2014 7.6. ATOMIC_AGGREGATE The attribute SHALL be considered malformed if its length is not 0 [RFC4271]. An UPDATE message with a malformed ATOMIC_AGGREGATE attribute SHALL be handled using the approach of "attribute discard". 7.7. AGGREGATOR The error conditions specified in [RFC4271] for the attribute are revised as follows: The AGGREGATOR attribute SHALL be considered malformed if any of the following applies: o Its length is not 6 (when the "4-octet AS number capability" is not advertised to, or not received from the peer [RFC6793]). o Its length is not 8 (when the "4-octet AS number capability" is both advertised to, and received from the peer). An UPDATE message with a malformed AGGREGATOR attribute SHALL be handled using the approach of "attribute discard". 7.8. Community The error handling of [RFC1997] is revised as follows: The Community attribute SHALL be considered malformed if its length is not a nonzero multiple of 4. An UPDATE message with a malformed Community attribute SHALL be handled using the approach of "treat-as-withdraw". 7.9. ORIGINATOR_ID The error handling of [RFC4456] is revised as follows. o If the ORIGINATOR_ID attribute is received from an external neighbor, it SHALL be discarded using the approach of "attribute discard", or o if received from an internal neighbor, it SHALL be considered malformed if its length is not equal to 4. If malformed, the UPDATE SHALL be handled using the approach of "treat-as-withdraw". Chen, et al. Expires December 15, 2014 [Page 12] Internet-Draft Revised Error Handling for BGP June 2014 7.10. CLUSTER_LIST The error handling of [RFC4456] is revised as follows. o If the CLUSTER_LIST attribute is received from an external neighbor, it SHALL be discarded using the approach of "attribute discard", or o if received from an internal neighbor, it SHALL be considered malformed if its length is not a nonzero multiple of 4. If malformed, the UPDATE SHALL be handled using the approach of "treat-as-withdraw". 7.11. MP_REACH_NLRI [RFC4760] references the error-handling of the base BGP specification for validation of the next hop. ("The rules for the next hop information are the same as the rules for the information carried in the NEXT_HOP BGP attribute".) Thus just as in Section 7.3 we must consider what it means for the Next Hop field of the MP_REACH attribute to be a "valid host address": o If the Next Hop field contains an IPv4 address (possibly as a sub- field), the field SHOULD be considered invalid if the IPv4 address appears in the ""IANA IPv4 Special-Purpose Address Registry" [IANA-IPV4] and either the "destination" or the "forwardable" boolean in that registry is given as "false". o If the Next Hop field contains an IPv6 address (possibly as a sub- field), the field SHOULD be considered invalid if the IPv6 address appears in the "IANA IPv6 Special-Purpose Address Registry" [IANA-IPV6], the address is not an IPv4-mapped IPv6 address, and either the "destination" or the "forwardable" boolean in that registry is given as "false". o If the Next Hop field contains an IPv4-mapped IPv6 address (possibly as a sub-field), the field SHOULD be considered invalid unless the use of such addresses has been explicitly allowed for the particular AFI/SAFI that occurs in this MP_REACH_NLRI attribute. (E.g., see [RFC4659] and [RFC4798].) o If the Next Hop field is some other form of address, it should be considered invalid in circumstances analogous to the above -- if it is found in the relevant IANA special-purpose address registry (if any) and its "destination" or "forwardable" boolean is given as "false". Chen, et al. Expires December 15, 2014 [Page 13] Internet-Draft Revised Error Handling for BGP June 2014 o An implementation SHOULD provide a means to modify the list of invalid host addresses by configuration -- these are sometimes referred to as "Martians". Section 3 and Section 5 provide further discussion of the handling of this attribute. 7.12. MP_UNREACH_NLRI Section 3 and Section 5 discuss the handling of this attribute. 7.13. Traffic Engineering path attribute We note that [RFC5543] does not detail what constitutes "malformation" for the Traffic Engineering path attribute. A future update to that specification may provide more guidance. In the interim, an implementation that determines (for whatever reason) that an UPDATE message contains a malformed Traffic Engineering path attribute MUST handle it using the approach of "treat-as-withdraw". 7.14. Extended Community The error handling of [RFC4360] is revised as follows: The Extended Community attribute SHALL be considered malformed if its length is not a nonzero multiple of 8. An UPDATE message with a malformed Extended Community attribute SHALL be handled using the approach of "treat-as-withdraw". Note that a BGP speaker MUST NOT treat an unrecognized Extended Community Type or Sub-Type as an error. 7.15. IPv6 Address Specific BGP Extended Community Attribute The error handling of [RFC5701] is revised as follows: The IPv6 Address Specific Extended Community attribute SHALL be considered malformed if its length is not a nonzero multiple of 20. An UPDATE message with a malformed IPv6 Address Specific Extended Community attribute SHALL be handled using the approach of "treat-as- withdraw". Note that a BGP speaker MUST NOT treat an unrecognized IPv6 Address Specific Extended Community Type or Sub-Type as an error. Chen, et al. Expires December 15, 2014 [Page 14] Internet-Draft Revised Error Handling for BGP June 2014 7.16. BGP Entropy Label Capability Attribute The error handling of [RFC6790] is revised as follows. No syntax errors are defined for the Entropy Label Capability attribute (ELCA). However, if any implementation does for some local reason determine that a syntax error exists with the ELCA, the error SHALL be handled using the approach of "attribute discard". 7.17. ATTR_SET The final paragraph of Section 5 of [RFC6368] is revised as follows: Old Text: An UPDATE message with a malformed ATTR_SET attribute SHALL be handled as follows. If its Partial flag is set and its Neighbor-Complete flag is clear, the UPDATE is treated as a route withdraw as discussed in [OPT-TRANS-BGP]. Otherwise (i.e., Partial flag is clear or Neighbor-Complete is set), the procedures of the BGP-4 base specification [RFC4271] MUST be followed with respect to an Optional Attribute Error. New Text: An UPDATE message with a malformed ATTR_SET attribute SHALL be handled using the approach of "treat as withdraw". Furthermore, the normative reference to [OPT-TRANS-BGP] in [RFC6368] is removed. 8. Guidance for Authors of BGP Specifications A document that specifies a new BGP attribute MUST provide specifics regarding what constitutes an error for that attribute and how that error is to be handled. Allowable error-handling approaches are detailed in Section 2. The treat-as-withdraw approach is generally preferred. The document SHOULD also provide consideration of what debugging facilities may be required to permit issues caused by a malformed attribute to be diagnosed. For any malformed attribute that is handled by the "attribute discard" instead of the "treat-as-withdraw" approach, it is critical to consider the potential impact of doing so. In particular, if the attribute in question has or may have an effect on route selection or installation, the presumption is that discarding it is unsafe, unless careful analysis proves otherwise. The analysis should take into Chen, et al. Expires December 15, 2014 [Page 15] Internet-Draft Revised Error Handling for BGP June 2014 account the tradeoff between preserving connectivity and potential side effects. Authors can refer to Section 7 for examples. 9. IANA Considerations This document makes no request of IANA. 10. Security Considerations This specification addresses the vulnerability of a BGP speaker to a potential attack whereby a distant attacker can generate a malformed optional transitive attribute that is not recognized by intervening routers (which thus propagate the attribute unchecked) but that causes session resets when it reaches routers that do recognize the given attribute type. In other respects, this specification does not change BGP's security characteristics. 11. Acknowledgements The authors wish to thank Juan Alcaide, Deniz Bahadir, Ron Bonica, Mach Chen, Andy Davidson, Bruno Decraene, Rex Fernando, Jeff Haas, Chris Hall, Joel Halpern, Dong Jie, Akira Kato, Miya Kohno, Tony Li, Alton Lo, Shin Miyakawa, Tamas Mondal, Jonathan Oddy, Tony Przygienda, Robert Raszuk, Yakov Rekhter, Eric Rosen, Shyam Sethuram, Rob Shakir, Naiming Shen, Adam Simpson, Ananth Suryanarayana, Kaliraj Vairavakkalai, Lili Wang and Ondrej Zajicek for their observations and discussion of this topic, and review of this document. 12. References 12.1. Normative References [IANA-BGP-ATTRS] "BGP Path Attributes", . [IANA-IPV4] "IANA IPv4 Special-Purpose Address Registry", . Chen, et al. Expires December 15, 2014 [Page 16] Internet-Draft Revised Error Handling for BGP June 2014 [IANA-IPV6] "IANA IPv4 Special-Purpose Address Registry", . [RFC1997] Chandrasekeran, R., Traina, P., and T. Li, "BGP Communities Attribute", RFC 1997, August 1996. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, January 2006. [RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended Communities Attribute", RFC 4360, February 2006. [RFC4456] Bates, T., Chen, E., and R. Chandra, "BGP Route Reflection: An Alternative to Full Mesh Internal BGP (IBGP)", RFC 4456, April 2006. [RFC4724] Sangli, S., Chen, E., Fernando, R., Scudder, J., and Y. Rekhter, "Graceful Restart Mechanism for BGP", RFC 4724, January 2007. [RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, "Multiprotocol Extensions for BGP-4", RFC 4760, January 2007. [RFC5543] Ould-Brahim, H., Fedyk, D., and Y. Rekhter, "BGP Traffic Engineering Attribute", RFC 5543, May 2009. [RFC5701] Rekhter, Y., "IPv6 Address Specific BGP Extended Community Attribute", RFC 5701, November 2009. [RFC6368] Marques, P., Raszuk, R., Patel, K., Kumaki, K., and T. Yamagata, "Internal BGP as the Provider/Customer Edge Protocol for BGP/MPLS IP Virtual Private Networks (VPNs)", RFC 6368, September 2011. [RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and L. Yong, "The Use of Entropy Labels in MPLS Forwarding", RFC 6790, November 2012. [RFC6793] Vohra, Q. and E. Chen, "BGP Support for Four-Octet Autonomous System (AS) Number Space", RFC 6793, December 2012. Chen, et al. Expires December 15, 2014 [Page 17] Internet-Draft Revised Error Handling for BGP June 2014 12.2. Informative References [I-D.ietf-l2vpn-evpn] Sajassi, A., Aggarwal, R., Bitar, N., Isaac, A., and J. Uttaro, "BGP MPLS Based Ethernet VPN", draft-ietf-l2vpn- evpn-07 (work in progress), May 2014. [RFC4659] De Clercq, J., Ooms, D., Carugi, M., and F. Le Faucheur, "BGP-MPLS IP Virtual Private Network (VPN) Extension for IPv6 VPN", RFC 4659, September 2006. [RFC4798] De Clercq, J., Ooms, D., Prevost, S., and F. Le Faucheur, "Connecting IPv6 Islands over IPv4 MPLS Using IPv6 Provider Edge Routers (6PE)", RFC 4798, February 2007. [RFC6514] Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP Encodings and Procedures for Multicast in MPLS/BGP IP VPNs", RFC 6514, February 2012. [RFC7117] Aggarwal, R., Kamite, Y., Fang, L., Rekhter, Y., and C. Kodeboniya, "Multicast in Virtual Private LAN Service (VPLS)", RFC 7117, February 2014. Authors' Addresses Enke Chen (editor) Cisco Systems, Inc. Email: enkechen@cisco.com John G. Scudder (editor) Juniper Networks Email: jgs@juniper.net Pradosh Mohapatra Sproute Networks Email: mpradosh@yahoo.com Keyur Patel Cisco Systems, Inc. Email: keyupate@cisco.com Chen, et al. Expires December 15, 2014 [Page 18]