--- 1/draft-ietf-idr-error-handling-02.txt 2012-11-21 21:15:35.949342567 +0100 +++ 2/draft-ietf-idr-error-handling-03.txt 2012-11-21 21:15:35.969342235 +0100 @@ -1,33 +1,33 @@ Internet Engineering Task Force (IETF) J. Scudder Internet Draft Juniper Networks -Update: 1997, 4271, 4360 (if approved) E. Chen +Update: 1997, 4271, 4360, 5701 (if approved) E. Chen Intended Status: Standards Track P. Mohapatra -Expires: December 18, 2012 K. Patel +Expires: May 22, 2013 K. Patel Cisco Systems - June 17, 2012 + November 21, 2012 Revised Error Handling for BGP UPDATE Messages - draft-ietf-idr-error-handling-02.txt + draft-ietf-idr-error-handling-03.txt 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 several existing attributes. + the error handling procedures for a number of existing attributes. Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. @@ -36,21 +36,21 @@ 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html - This Internet-Draft will expire on December 18, 2012. + This Internet-Draft will expire on May 22, 2013. Copyright Notice Copyright (c) 2012 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 @@ -79,23 +79,23 @@ 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. 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 several existing attributes. Specifically, the error - handling procedures of [RFC4271], [RFC1997], and [RFC4360] are - revised. + procedures for a number of existing attributes. Specifically, the + error handling procedures of [RFC4271], [RFC1997], [RFC4360] and + [RFC5701] are revised. 1.1. Specification of Requirements 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. Revision to Base Specification The first paragraph of Section 6.3 of [RFC4271] is revised as @@ -126,79 +126,91 @@ The error handling of the following case described in Section 6.3 of [RFC4271] is revised 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). as follows: - If any attribute has Attribute Flags that conflict with the - Attribute Type Code, then the error SHOULD be logged, and the + If the "Optional bit" or the "Transitive bit" in the Attribute + Flags for an attribute conflicts with the Attribute Type Code, + then the error SHOULD be logged, and the conflicting bit in the Attribute Flags MUST be reset to the correct value. The UPDATE message MUST continue to be processed. The error handling of all other cases described in Section 6.3 of [RFC4271] that specify a session reset is revised as follows. - When a path attribute in an UPDATE message is determined to be - malformed, the UPDATE message containing that attribute 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 [RFC4760bis] if appropriate) of the UPDATE - message, thus causing them to be removed from the Adj-RIB-In - according to the procedures of [RFC4271]. In the case of an + When a path attribute (other than the MP_REACH_NLRI attribute + [RFC4760] or the MP_UNREACH_NLRI attribute [RFC4760]) in an UPDATE + message is determined to be malformed, the UPDATE message containing + that attribute 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]. In the case of an attribute which has no effect on route selection or installation, the malformed attribute MAY instead be discarded and the UPDATE message continue to be processed. For the sake of brevity, the former approach is termed "treat-as-withdraw", and the latter as "attribute discard". + If any of the well-known mandatory attributes are not present in an + UPDATE message, then the approach of "treat-as-withdraw" MUST be used + for the error handling. + The approach of "treat-as-withdraw" MUST be used for the error handling of the cases described in Section 6.3 of [RFC4271] that specify a session reset and involve any of the following attributes: ORIGIN, AS_PATH, NEXT_HOP, MULTI_EXIT_DISC, and LOCAL_PREF. The approach of "attribute discard" MUST be used for the error handling of the cases described in Section 6.3 of [RFC4271] that specify a session reset and involve any of the following attributes: ATOMIC_AGGREGATE and AGGREGATOR. - If an attribute 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. + If the MP_REACH_NLRI attribute or the MP_UNREACH_NLRI 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 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. When multiple malformed attributes exist in an UPDATE message, if the - same approach (either "treat-as-withdraw" or "attribute discard") is - specified for the handling of these malformed attributes, then the - specified approach MUST be used. Otherwise "treat-as-withdraw" MUST - be used. + same approach (either "session reset", or "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 following the order + of "session reset", "treat-as-withdraw" and "attribute discard" from + the strongest to the weakest. A document which specifies a new attribute MUST provide specifics regarding what constitutes an error for that attribute and how that error is to be handled. Finally, we observe that in order to use the approach of "treat-as- - withdraw", the entire NLRI field and/or MP_REACH and MP_UNREACH - [RFC4760bis] attributes need to be successfully parsed. If this is - not possible, the procedures of [RFC4271] continue to apply. - Alternatively the error handling procedures specified in [RFC4760bis] + withdraw", the entire NLRI field and/or the MP_REACH_NLRI and + MP_UNREACH_NLRI attributes need to be successfully parsed. If this + is not possible, the procedures of [RFC4271] continue to apply. + Alternatively the error handling procedures specified in [RFC4760] for disabling a particular AFI/SAFI MAY be followed. 3. Parsing of NLRI Fields To facilitate the determination of the NLRI field in an UPDATE with a - malformed attribute, the MP_REACH or MP_UNREACH attribute (if - present) SHOULD be encoded as the very first path attribute in an - UPDATE as recommended by [RFC4760bis]. An implementation, however, - MUST still be prepared to receive these fields in any position. + malformed attribute, the MP_REACH_NLRI or MP_UNREACH_NLRI attribute + (if present) SHALL be encoded as the very first path attribute in an + UPDATE. An implementation, however, MUST still be prepared to + receive these fields in any position. 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. 4. Operational Considerations @@ -240,85 +252,160 @@ side effects. 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. -5. Error Handling Procedures for Existing Optional Attributes +5. Error Handling Procedures for Existing Attributes -5.1. AGGREGATOR +5.1. ORIGIN - The error handling of [RFC4271] is revised as follows: + 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". + +5.2. AS_PATH + + The error conditions for the attribute have been defined in + [RFC4271]. + + An UPDATE message with a malformed AS_PATH attribute SHALL be handled + using the approach of "treat-as-withdraw". + +5.3. NEXT_HOP + + The error conditions for the NEXT_HOP attribute have been defined in + [RFC4271]. + + An UPDATE message with a malformed NEXT_HOP attribute SHALL be + handled using the approach of "treat-as-withdraw". + +5.4. MULTI_EXIT_DESC + + The attribute is considered malformed if its length is not 4 + [RFC4271]. + + An UPDATE message with a malformed MULTI_EXIT_DESC attribute SHALL be + handled using the approach of "treat-as-withdraw". + +5.5. LOCAL_PREF + + The attribute is considered malformed if its length is not 4 + [RFC4271]. + + An UPDATE message with a malformed LOCAL_PREF attribute SHALL be + handled as follows: + + o using the approach of "attribute discard" if the UPDATE message + is received from an external neighbor, or + + o using the approach of "treat-as-withdraw" if the UPDATE message + is received from an internal neighbor. + + In addition, if the attribute is present in an UPDATE message from an + external neighbor, the approach of "attribute discard" SHALL be used + to handle the unexpected attribute in the message. + +5.6. 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". + +5.7. 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 [RFC4893]). 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". -5.2. Community +5.8. 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. + is nonzero and is not a multiple of 4. An UPDATE message with a malformed Community attribute SHALL be handled using the approach of "treat-as-withdraw". -5.3. Extended Community +5.9. 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. + length is nonzero and is not a 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. +5.10. 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 nonzero and is not a 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. + 6. IANA Considerations This document makes no request of IANA. 7. 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. 8. Acknowledgments - The authors wish to thank Ron Bonica, Mach Chen, Andy Davidson, Dong - Jie, Rex Fernando, Joel Halpern, Akira Kato, Miya Kohno, Tony Li, - Alton Lo, Shin Miyakawa, Tamas Mondal, Jonathan Oddy, Robert Raszuk, - Yakov Rekhter, Rob Shakir, Naiming Shen, Shyam Sethuram, Ananth - Suryanarayana, and Kaliraj Vairavakkalai for their observations and - discussion of this topic, and review of this document. + The authors wish to thank Juan Alcaide, Ron Bonica, Mach Chen, Andy + Davidson, Bruno Decraene, Dong Jie, Rex Fernando, Joel Halpern, Akira + Kato, Miya Kohno, Tony Li, Alton Lo, Shin Miyakawa, Tamas Mondal, + Jonathan Oddy, Robert Raszuk, Yakov Rekhter, Rob Shakir, Naiming + Shen, Shyam Sethuram, Ananth Suryanarayana, Kaliraj Vairavakkalai and + Lili Wang for their observations and discussion of this topic, and + review of this document. 9. Normative References [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 @@ -327,25 +414,26 @@ [RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended Communities Attribute", RFC 4360, February 2006. [RFC4893] Vohra, Q. and E. Chen, "BGP Support for Four-octet AS Number Space", RFC 4893, May 2007. [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008. - [RFC4760bis] - Bates, T., Chandra, R., Katz, D., and Y. Rekhter, - "Multiprotocol Extensions for BGP-4", - draft-ietf-idr-rfc4760bis-03.txt, work in progress, - August 2011. + [RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, + "Multiprotocol Extensions for BGP-4", RFC 4760, + January 2007. + + [RFC5701] Rekhter, Y., "IPv6 Address Specific BGP Extended + Community Attribute", RFC 5701, November 2009. Appendix A. Why not discard UPDATE messages? A commonly asked question is "why not simply discard the UPDATE message instead of treating it like a withdraw? Isn't that safer and easier?" The answer is that it might be easier, but it would compromise BGP's correctness so is unsafe. Consider the following example of what might happen if UPDATE messages carrying bad attributes were simply discarded: