Network Working Group H. Chen Internet-Draft China Telecom Intended status: Best Current Practice D. Ma Expires: October 4, 2019 ZDNS Y. Gu S. Zhuang H. Wang Huawei April 2, 2019 Enhanced AS-Loop Detection for BGP draft-chen-grow-enhanced-as-loop-detection-01 Abstract This document proposes to enhance AS-Loop Detection for BGP Inbound/ Outbound Route Processing. This could empower networks to quickly and accurately figure out they're being victimized. 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]. 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 https://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 October 4, 2019. Copyright Notice Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved. Chen, et al. Expires October 4, 2019 [Page 1] Internet-Draft Enhanced AS-Loop Detection April 2019 This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Enhanced AS-Loop Detection for BGP Inbound Route Processing . 5 4. Enhanced AS-Loop Detection for BGP Outbound Route Processing 7 5. Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . 8 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 8. Security Considerations . . . . . . . . . . . . . . . . . . . 9 9. Normative References . . . . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 1. Introduction The Border Gateway Protocol (BGP) [RFC4271], as an inter-Autonomous (AS) routing protocol, is used to exchange network reachability information between BGP systems. BGP is widely used by Internet Service Providers (ISPs) and large organizations. BGP is used to exchange reachable inter-AS routes, establish inter-AS paths, avoid routing loops, and apply routing policies between ASs. BGP loop detection mechanism is defined in section 9.1.2. of RFC4271: ... If the AS_PATH attribute of a BGP route contains an AS loop, the BGP route should be excluded from the Phase 2 decision function. AS loop detection is done by scanning the full AS path (as specified in the AS_PATH attribute), and checking that the autonomous system number of the local system does not appear in the AS path. Operations of a BGP speaker that is configured to accept routes with its own autonomous system number in the AS path are outside the scope of this document. ... Chen, et al. Expires October 4, 2019 [Page 2] Internet-Draft Enhanced AS-Loop Detection April 2019 In ordinary BGP, every AS announces its route information with different prefixes. However, its neighboring ASes cannot validate this route information, but rather directly propagate it across the Internet or simply discard AS-Loop routes directly. Obviously, this weak trust model allows forged route announcement propagations and rarely been found, which is a fundamental security weakness of BGP. Forged routes, which can be generated by configuration errors or malicious attacks, can cause large-scale network connectivity problems. Some cases can be worse, hackers exploit this property of BGP to achieve their ulterior motives. They can add some providers' AS number into the forged AS-Path and attempt to make it look like the route had passed through these ASNs, or perhaps they are there to prevent those providers from carrying the route. For example, the cases shown in Figure 1. o Forged Case 1: One upstream ISP of AS64596 forged a route with the ASN 64596 as the origin ASN in the AS-Path. o Forged Case 2: One upstream ISP of AS64596 forged a route with the ASN 64596 as the transit ASN in the AS-Path. After receiving the above routes, AS64596 treats them as normal loop routes during the loop detecting phase and discards them directly. In most NOSes (Netwok Operation Systems), such rejected routes are not logged and only visable by puuting the router into debugging mode. If the AS64596 is slightly enhanced, it can find that someone has faked himself, which may cause unnecessary trouble for himself. Chen, et al. Expires October 4, 2019 [Page 3] Internet-Draft Enhanced AS-Loop Detection April 2019 AS-Loop-Detecting at this point Discard AS-Loop Routes directly that contains AS64596 | | v x.y.z.0/24 Origin AS 64600 AS64595---AS64596---AS64597---AS64598---AS64599----AS64600 Normal Case: <-- x.y.z.0/24, AS-Path: 64597 64598 64599 64600 Forged Case 1: <-- x.y.z.0/24, AS-Path: 64597 64596 (Or: 64597 64598 64596 etc.) Forged Case 2: <-- x.y.z.0/24, AS-Path: 64597 64596 64600 (Or: 64597 64596 64599 64600 etc.) Figure 1: BGP Inbound Route Processing Split-Horizon for EBGP is an optional function that a BGP sender will not advertise any routes that were previously received from that same AS. In some current implementation, the BGP outbound route processing step will simply discard the route if AS-Loop being detected. For example, the cases shown in Figure 1. o Forged Case 1: One upstream ISP of AS64597 forged a route with the ASN 64596 as the origin ASN in the AS-Path. o Forged Case 2: One upstream ISP of AS64597 forged a route with the ASN 64596 as the transit ASN in the AS-Path. When sending the above routes, AS64597 treats them as normal loop routes and discards them directly. If AS64597 is slightly enhanced, it can find that someone has faked AS64596, which may cause large- scale network connectivity problems. Chen, et al. Expires October 4, 2019 [Page 4] Internet-Draft Enhanced AS-Loop Detection April 2019 Split-Horizon Enable & AS-Loop-Detecting at this point Discard AS-Loop Routes directly if sending AS-Path contains AS64596 | | v x.y.z.0/24 Origin AS 64600 AS64595---AS64596---AS64597---AS64598---AS64599----AS64600 Normal Case: <-- x.y.z.0/24, AS-Path: 64597 64598 64599 64600 Forged Case 1: <-- x.y.z.0/24, AS-Path: 64597 64596 (Or: 64597 64598 64596 etc.) Forged Case 2: <-- x.y.z.0/24, AS-Path: 64597 64596 64600 (Or: 64597 64596 64599 64600 etc.) Figure 2: BGP Outbound Route Processing Above cases are also being known As-Path Poisoning Attacks. This document proposes to enhance AS-Loop Detection for BGP Inbound/ Outbound Route Processing. This could empower networks to quickly and accurately figure out they're being victimized. 2. Terminology The following terminology is used in this document. AS: Autonomous System BGP: Border Gateway Protocol BGP hijacking : is the illegitimate takeover of groups of IP addresses by corrupting Internet routing tables maintained using the Border Gateway Protocol (BGP). (Sometimes referred to as prefix hijacking, route hijacking or IP hijacking) EBGP: External BGP ISP: Internet Service Provider 3. Enhanced AS-Loop Detection for BGP Inbound Route Processing This section proposes to enhance AS Loop Detection for BGP Inbound Route Processing. Chen, et al. Expires October 4, 2019 [Page 5] Internet-Draft Enhanced AS-Loop Detection April 2019 As shown in Figure 3, when receiving the routes from AS64597, AS64596 should check whether its AS number is already in the AS-Path, If yes, it further analyzes the location of the AS64596 in the received AS_Path: Case 1: AS 64596 is listed as Origin AS in the AS-Path Lookup the local resource database (Such as ROA Cache) and determine whether the route is originated from the AS 64596. o Result 1: AS 64596 has no corresponding prefix; it is identified as a purely forged AS_Path prefix hijacking event, which is recorded as incident type 1. o Result 2: The corresponding prefix is a sub-prefix of a certain prefix of the AS 64596 and the AS 64596 has not advertise it. For example, the prefix being hold by the AS 64596 is 10.10.128.0/17, and the receiving route prefix is 10.10.192.0/24, the latter is a sub-prefix of the former, which indicates that this is a forged AS_Path sub-prefix hijacking event, which is recorded as incident type 2. o Result 3: The corresponding prefix is a sub-prefix of a certain prefix of the AS 64596 and the AS 64596 has only advertised to some special ASNs, and only wants it to be used internally by those ASNs. The AS 64596 recognizes that At least one special AS violates the route policy. Which is recorded as incident type 3. o Result 4: The corresponding prefix is originated by the AS 64596, this is the normal case. Case 2: AS 64596 is listed as transit AS in the AS-Path For example, AS-Path looks like the following form AS64596's perspective: (possible other AS), left AS, local AS(64596), right AS, (possible other AS) At this point, AS 64596 can lookup the local resource database and check whether there is a real AS relationship between the local AS and the left AS and the right AS. (From the perspective of the local AS, it can manage/hold the AS-relationship database between the local AS and each of its neighboring ASs (such as C2P, P2P, P2C, etc.).) o Result 1: At least one of the AS ( the left AS or the right AS) has no actual AS relationship with the local AS (i.e. A never Chen, et al. Expires October 4, 2019 [Page 6] Internet-Draft Enhanced AS-Loop Detection April 2019 before seen AS-AS adjacency). It is a purely forged AS_Path prefix hijacking event. Which is recorded as incident type 4. o Result 2: The AS relationships between the local AS and the left AS and the right AS are correct, but the local AS has not previously process this prefix , so it can be recognized that this is a forged route. We classify this incident type as type 5. o Result 3: The AS relationships between the AS and the left AS and the right AS are correct, and the local AS 64596 has previously processed the prefix, this is the normal case. Enhanced AS-Loop-Detecting at this point To identify the attack/forged information | | v x.y.z.0/24 Origin AS 64600 AS64595---AS64596---AS64597---AS64598---AS64599----AS64600 Normal Case: <-- x.y.z.0/24, AS-Path: 64597 64598 64599 64600 Forged Case 1: <-- x.y.z.0/24, AS-Path: 64596 64595 (Or: 64597 64598 64596 etc.) Forged Case 2: <-- x.y.z.0/24, AS-Path: 64597 64596 64600 (Or: 64597 64596 64599 64600 etc.) Figure 3: Enhance for BGP Inbound Route Processing The local AS 64596 inputs the detected result to the route hijacking management module, or/and records the log or/and the alarm information, and the maintenance team of the local AS 64596 can notify the maintenance team of the relevant AS to correct the error in their networks . After the above steps are added, the stability and security of the network can be improved. 4. Enhanced AS-Loop Detection for BGP Outbound Route Processing This section proposes to enhance AS Loop Detection for BGP Outbound Route Processing. Chen, et al. Expires October 4, 2019 [Page 7] Internet-Draft Enhanced AS-Loop Detection April 2019 If Split-Horizon Enable, Enhanced AS-Loop-Detecting at this point To identify the attack/forged information | | v x.y.z.0/24 Origin AS 64600 AS64595---AS64596---AS64597---AS64598---AS64599----AS64600 Normal Case: <-- x.y.z.0/24, AS-Path: 300 64598 64599 64600 Forged Case 1: <-- x.y.z.0/24, AS-Path: 64597 64596 (Or: 64597 64598 64596 etc.) Forged Case 2: <-- x.y.z.0/24, AS-Path: 64597 64596 64600 (Or: 64597 64596 64599 64600 etc.) Figure 4: Enhance for BGP Outbound Route Processing As shown in Figure 4, when sending the routes from AS64597 to AS64596, AS64597 will check whether the AS number 64596 is already in the AS-Path, If yes, it can further analyzes the location of the AS64596 in the received AS_Path: The remaining processing steps are the same as the previous section. 5. Benefits After the enhancements of the AS Loop Detection for BGP Inbound/ Outbound Route Processing are added, the stability and security of the network can be improved. 6. Acknowledgements The authors would like to acknowledge the review and inputs from Gang Yan, Zhenbin Li, Aijun Wang, Jeff Haas, Robert Razsuk, Alexander Asimov and the working group. . 7. IANA Considerations TBD. Chen, et al. Expires October 4, 2019 [Page 8] Internet-Draft Enhanced AS-Loop Detection April 2019 8. Security Considerations TBD. 9. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [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, . [RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, "Multiprotocol Extensions for BGP-4", RFC 4760, DOI 10.17487/RFC4760, January 2007, . [RFC7854] Scudder, J., Ed., Fernando, R., and S. Stuart, "BGP Monitoring Protocol (BMP)", RFC 7854, DOI 10.17487/RFC7854, June 2016, . Authors' Addresses Huanan Chen China Telecom 109, West Zhongshan Road, Tianhe District Guangzhou 510000 China Email: chenhn8.gd@chinatelecom.cn Di Ma ZDNS 4 South 4th St. Zhongguancun Beijing, Haidian China Email: madi@zdns.cn Chen, et al. Expires October 4, 2019 [Page 9] Internet-Draft Enhanced AS-Loop Detection April 2019 Yunan Gu Huawei Huawei Bld., No.156 Beiqing Rd. Beijing 100095 China Email: guyunan@huawei.com Shunwan Zhuang Huawei Huawei Bld., No.156 Beiqing Rd. Beijing 100095 China Email: zhuangshunwan@huawei.com Haibo Wang Huawei Huawei Bld., No.156 Beiqing Rd. Beijing 100095 China Email: rainsword.wang@huawei.com Chen, et al. Expires October 4, 2019 [Page 10]