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Network Working Group                                            H. Chen
Internet-Draft                                             China Telecom
Intended status: Best Current Practice                             Y. Gu
Expires: September 13, 2019                                    S. Zhuang
                                                                 H. Wang
                                                                  Huawei
                                                          March 12, 2019


                   Enhanced AS-Loop Detection for BGP
             draft-chen-grow-enhanced-as-loop-detection-00

Abstract

   This document proposes to enhance AS-Loop Detection for BGP Inbound/
   Outbound Route Processing.

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 September 13, 2019.

Copyright Notice

   Copyright (c) 2019 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
   (https://trustee.ietf.org/license-info) in effect on the date of



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   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 . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Enhanced AS-Loop Detection for BGP Inbound Route Processing .   5
   4.  Enhanced AS-Loop Detection for BGP Outbound Route Processing    7
   5.  Benefits  . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

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.

      ...

   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



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   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 AS200 forged a route with the
      ASN 200 as the origin ASN.

   o  Forged Case 2: One upstream ISP of AS200 forged a route with the
      ASN 200 as the transit ASN.

   After receiving the above routes, AS200 treats them as normal loop
   routes during the loop detecting phase and discards them directly.
   If the AS200 is slightly enhanced, it can find that someone has faked
   himself, which may cause unnecessary trouble for himself.

      AS-Loop-Detecting at this point
      Discard AS-Loop Routes directly that contains AS200
              |
              |
              v                                 x.y.z.0/24 Origin AS 600
 AS100---AS200---AS300-----AS400-----AS500------AS600
                 Normal Case:
                 <-- x.y.z.0/24, AS-Path: 300 400 500 600

                 Forged Case 1:
                 <-- x.y.z.0/24, AS-Path: 300 200
                                 (Or: 300 400 200 etc.)

                 Forged Case 2:
                 <-- x.y.z.0/24, AS-Path: 300 200 600
                                 (Or: 300 200 500 600 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



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   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 AS300 forged a route with the
      ASN 200 as the origin ASN.

   o  Forged Case 2: One upstream ISP of AS300 forged a route with the
      ASN 200 as the transit ASN.

   When sending the above routes, AS300 treats them as normal loop
   routes and discards them directly.  If AS300 is slightly enhanced, it
   can find that someone has faked AS200, which may cause large-scale
   network connectivity problems.

      Split-Horizon Enable & AS-Loop-Detecting at this point
      Discard AS-Loop Routes directly if sending AS-Path contains AS200
                |
                |
                v                               x.y.z.0/24?Origin AS 600
 AS100---AS200---AS300-----AS400-----AS500------AS600
                 Normal Case:
                 <-- x.y.z.0/24, AS-Path: 300 400 500 600

                 Forged Case 1:
                 <-- x.y.z.0/24, AS-Path: 300 200
                                 (Or: 300 400 200 etc.)

                 Forged Case 2:
                 <-- x.y.z.0/24, AS-Path: 300 200 600
                                 (Or: 300 200 500 600 etc.)

     Figure 2: BGP Outbound Route Processing

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)




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   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.

   As shown in Figure 3, when receiving the routes from AS300, AS200
   should check whether its AS number is already in the AS-Path, If yes,
   it further analyzes the location of the AS200 in the received
   AS_Path:

   Case 1: AS 200 is listed as Origin AS

   Lookup the local resource database (Such as ROA Cache) and determine
   whether the route is originated from the AS 200.

   o  Result 1: AS 200 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 200 and the AS 200 has not advertise it.  For
      example, the prefix being hold by the AS 200 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 200 and the AS 200 has only advertised to some
      special ASNs, and only wants it to be used internally by those
      ASNs.  The AS 200 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 200,
      this is the normal case.

   Case 2: AS 200 is listed as transit AS

   For example, AS-Path looks like the following form:

   (possible other AS), left AS, local AS(200), right AS, (possible
   other AS)





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   At this point, AS 200 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

   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.  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 is 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  Detection result 3: The AS relationship between the AS and the
      left AS and the right AS is correct, and the local AS 200 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 600
 AS100---AS200---AS300-----AS400-----AS500------AS600
                 Normal Case:
                 <-- x.y.z.0/24, AS-Path: 300 400 500 600

                 Forged Case 1:
                 <-- x.y.z.0/24, AS-Path: 300 200
                                 (Or: 300 400 200 etc.)

                 Forged Case 2:
                 <-- x.y.z.0/24, AS-Path: 300 200 600
                                 (Or: 300 200 500 600 etc.)

    Figure 3: Enhance for BGP Inbound Route Processing

   The local AS 200 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 200 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.






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4.  Enhanced AS-Loop Detection for BGP Outbound Route Processing

   This section proposes to enhance AS Loop Detection for BGP Outbound
   Route Processing.

     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 600
 AS100---AS200---AS300-----AS400-----AS500------AS600
                 Normal Case:
                 <-- x.y.z.0/24, AS-Path: 300 400 500 600

                 Forged Case 1:
                 <-- x.y.z.0/24, AS-Path: 300 200
                                 (Or: 300 400 200 etc.)

                 Forged Case 2:
                 <-- x.y.z.0/24, AS-Path: 300 200 600
                                 (Or: 300 200 500 600 etc.)

     Figure 4: Enhance for BGP Outbound Route Processing

   As shown in Figure 4, when sending the routes from AS300 to AS200,
   AS300 will check whether the AS number 200 is already in the AS-Path,
   If yes, it can further analyzes the location of the AS200 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 and Zhenbin Li.

   .








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7.  IANA Considerations

   TBD.

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,
              <https://www.rfc-editor.org/info/rfc2119>.

   [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,
              <https://www.rfc-editor.org/info/rfc4271>.

   [RFC4760]  Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
              "Multiprotocol Extensions for BGP-4", RFC 4760,
              DOI 10.17487/RFC4760, January 2007,
              <https://www.rfc-editor.org/info/rfc4760>.

   [RFC7854]  Scudder, J., Ed., Fernando, R., and S. Stuart, "BGP
              Monitoring Protocol (BMP)", RFC 7854,
              DOI 10.17487/RFC7854, June 2016,
              <https://www.rfc-editor.org/info/rfc7854>.

Authors' Addresses

   Huanan Chen
   China Telecom
   109, West Zhongshan Road, Tianhe District
   Guangzhou  510000
   China

   Email: chenhn8.gd@chinatelecom.cn


   Yunan Gu
   Huawei
   Huawei Bld., No.156 Beiqing Rd.
   Beijing  100095
   China

   Email: guyunan@huawei.com



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   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



































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