--- 1/draft-ietf-idr-error-handling-07.txt 2014-05-13 18:14:19.252071848 -0700 +++ 2/draft-ietf-idr-error-handling-08.txt 2014-05-13 18:14:19.288072701 -0700 @@ -1,55 +1,55 @@ Internet Engineering Task Force E. Chen, Ed. Internet-Draft Cisco Systems, Inc. Updates: 1997, 4271, 4360, 4456, 4760, 5701 (if approved)J. Scudder, Ed. Intended status: Standards Track Juniper Networks -Expires: November 8, 2014 P. Mohapatra +Expires: November 15, 2014 P. Mohapatra Sproute Networks K. Patel Cisco Systems, Inc. - May 7, 2014 + May 14, 2014 Revised Error Handling for BGP UPDATE Messages - draft-ietf-idr-error-handling-07 + draft-ietf-idr-error-handling-08 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, and 5701. + 4760 and 5701. 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 November 8, 2014. + This Internet-Draft will expire on November 15, 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 @@ -67,235 +67,264 @@ 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 . . . . . . . . . . . . . . . . . . 3 - 2. Revision to Base Specification . . . . . . . . . . . . . . . 4 - 3. Parsing of NLRI Fields . . . . . . . . . . . . . . . . . . . 6 - 3.1. Inconsistency of Attribute Length Fields . . . . . . . . 6 - 3.2. Syntactic Correctness of NLRI Fields . . . . . . . . . . 7 - 3.3. Typed NLRI . . . . . . . . . . . . . . . . . . . . . . . 7 - 4. Operational Considerations . . . . . . . . . . . . . . . . . 8 - 5. Error Handling Procedures for Existing Attributes . . . . . . 9 - 5.1. ORIGIN . . . . . . . . . . . . . . . . . . . . . . . . . 9 - 5.2. AS_PATH . . . . . . . . . . . . . . . . . . . . . . . . . 9 - 5.3. NEXT_HOP . . . . . . . . . . . . . . . . . . . . . . . . 9 - 5.4. MULTI_EXIT_DESC . . . . . . . . . . . . . . . . . . . . . 9 - 5.5. LOCAL_PREF . . . . . . . . . . . . . . . . . . . . . . . 9 - 5.6. ATOMIC_AGGREGATE . . . . . . . . . . . . . . . . . . . . 10 - 5.7. AGGREGATOR . . . . . . . . . . . . . . . . . . . . . . . 10 - 5.8. Community . . . . . . . . . . . . . . . . . . . . . . . . 10 - 5.9. Extended Community . . . . . . . . . . . . . . . . . . . 10 - 5.10. IPv6 Address Specific BGP Extended Community Attribute . 11 - 5.11. ORIGINATOR_ID . . . . . . . . . . . . . . . . . . . . . . 11 - 5.12. CLUSTER_LIST . . . . . . . . . . . . . . . . . . . . . . 11 - 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 - 7. Security Considerations . . . . . . . . . . . . . . . . . . . 12 - 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 - 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 - 9.1. Normative References . . . . . . . . . . . . . . . . . . 12 - 9.2. Informative References . . . . . . . . . . . . . . . . . 13 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13 + 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4 + 2. Error-Handling Approaches . . . . . . . . . . . . . . . . . . 4 + 3. Revision to BGP UPDATE Message Error Handling . . . . . . . . 4 + 4. Parsing of NLRI Fields . . . . . . . . . . . . . . . . . . . 6 + 4.1. Attribute Length Fields . . . . . . . . . . . . . . . . . 7 + 4.2. Syntactic Correctness of NLRI Fields . . . . . . . . . . 7 + 4.3. Typed NLRI . . . . . . . . . . . . . . . . . . . . . . . 8 + 5. Operational Considerations . . . . . . . . . . . . . . . . . 8 + 6. Error Handling Procedures for Existing Attributes . . . . . . 9 + 6.1. ORIGIN . . . . . . . . . . . . . . . . . . . . . . . . . 9 + 6.2. AS_PATH . . . . . . . . . . . . . . . . . . . . . . . . . 9 + 6.3. NEXT_HOP . . . . . . . . . . . . . . . . . . . . . . . . 10 + 6.4. MULTI_EXIT_DISC . . . . . . . . . . . . . . . . . . . . . 10 + 6.5. LOCAL_PREF . . . . . . . . . . . . . . . . . . . . . . . 10 + 6.6. ATOMIC_AGGREGATE . . . . . . . . . . . . . . . . . . . . 10 + 6.7. AGGREGATOR . . . . . . . . . . . . . . . . . . . . . . . 11 + 6.8. Community . . . . . . . . . . . . . . . . . . . . . . . . 11 + 6.9. Extended Community . . . . . . . . . . . . . . . . . . . 11 + 6.10. IPv6 Address Specific BGP Extended Community Attribute . 11 + 6.11. ORIGINATOR_ID . . . . . . . . . . . . . . . . . . . . . . 12 + 6.12. CLUSTER_LIST . . . . . . . . . . . . . . . . . . . . . . 12 + 6.13. MP_REACH_NLRI and MP_UNREACH_NLRI . . . . . . . . . . . . 12 + 7. Guidance for Authors of BGP Specifications . . . . . . . . . 12 + 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 + 9. Security Considerations . . . . . . . . . . . . . . . . . . . 13 + 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13 + 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 + 11.1. Normative References . . . . . . . . . . . . . . . . . . 13 + 11.2. Informative References . . . . . . . . . . . . . . . . . 14 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 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. + 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. 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], + error handling procedures of [RFC1997], [RFC4271], [RFC4360], [RFC4456], [RFC4760] and [RFC5701] 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. Revision to Base Specification +2. Error-Handling Approaches - The first paragraph of Section 6.3 of [RFC4271] is revised as - follows: + In this document we refer to three 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 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 6 for treatment of specific path attributes. + + a. The first paragraph is revised as follows: 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. + 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. + 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. - The error handling of the following case described in Section 6.3 of - [RFC4271] remains unchanged: + 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. + 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. - The error handling of the following case described in Section 6.3 of - [RFC4271] is revised + c. Attribute Flag error handling is revised as follows: - 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). + Old Text: - as follows: + 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). - If any recognized attribute has Attribute Flags that conflict with - the Attribute Type Code, then the attribute MUST be treated as - malformed and the treat-as-withdraw approach (see below) used, - unless the specification for the attribute mandates different - handling for incorrect Attribute Flags. + New Text: - The error handling of all other cases involving path attributes as - described in Section 6.3 of [RFC4271] that specify a session reset is - revised as follows. + If any recognized attribute has Attribute Flags that + conflict with the Attribute Type Code, 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. - 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". + d. If any of the well-known mandatory attributes are not present in + an UPDATE message, then "treat-as-withdraw" MUST be used. - 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. + 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. - 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. + f. "Attribute discard" MUST be used for any of the cases that + specify a session reset and involve ATOMIC_AGGREGATE or + AGGREGATOR. - 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. + 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 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. + 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. - When multiple attribute errors exist in an UPDATE message, if the - 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. + 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 4.2. - 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. + 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. If + this is not possible, the procedures of [RFC4271] continue to + apply, meaning that the "session reset" approach SHOULD be + followed. Alternatively the error handling procedures specified + in [RFC4760] for disabling a particular AFI/SAFI MAY be followed. - 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. If this - is not possible, the procedures of [RFC4271] continue to apply, - meaning that the session MUST be reset and a NOTIFICATION sent. - Alternatively the error handling procedures specified in [RFC4760] - for disabling a particular AFI/SAFI MAY be followed. One notable - case where it would be not possible to successfully parse the NLRI is - if the NLRI field is found to be "syntactically incorrect" (see - Section 3.2). It can be seen that therefore, this part of [RFC4271] - Section 6.3 necessarily continues to apply: + One notable case where it would be not possible to successfully + parse the NLRI is if the NLRI field is found to be "syntactically + incorrect" (see Section 4.2). It can be seen that therefore, + this part of [RFC4271] Section 6.3 necessarily continues to + apply: The NLRI field in the UPDATE message is checked for syntactic - validity. If the field is syntactically incorrect, then the Error - Subcode MUST be set to Invalid Network Field. - - Furthermore, this document extends RFC 4271 by mandating that the - Withdrawn Routes field SHALL be checked for syntactic correctness in - the same manner as the NLRI field. + validity. If the field is syntactically incorrect, then the + Error Subcode MUST be set to Invalid Network Field. -3. Parsing of NLRI Fields +4. Parsing of NLRI Fields To facilitate the determination of the NLRI field in an UPDATE with a - 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. + malformed attribute, the following restrictions on encoding NLRI MUST + be followed: + + 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 The MP_REACH_NLRI or MP_UNREACH_NLRI SHALL NOT be combined in the + same UPDATE message. + + o The MP_REACH_NLRI and MP_UNREACH_NLRI attributes MUST NOT be used + in an UPDATE that also contains a non-empty Withdrawn Routes or + Network Layer Reachability Information field. + + In all these cases, however, 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. -3.1. Inconsistency of Attribute Length Fields +4.1. 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 bytes remain, or fewer than four bytes, if the Attribute Flags - field has the Extended Length bit set -- that is, there remains + 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 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. -3.2. Syntactic Correctness of NLRI Fields + 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.) + +4.2. 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. @@ -309,35 +338,35 @@ 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 attribute is less than 3, or the length of the MP_REACH attribute is less than 5. -3.3. Typed NLRI +4.3. Typed NLRI Certain address families, for example MVPN [RFC7117] and EVPN [I-D.ietf-l2vpn-evpn] have NLRI that are typed. Since supported type - values with the address family are not expressed in the MP-BGP + 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 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. -4. Operational Considerations +5. 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. @@ -351,206 +380,241 @@ 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. - For any malformed attribute which 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 - account the tradeoff between preserving connectivity and potential - 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 Attributes +6. Error Handling Procedures for Existing Attributes -5.1. ORIGIN + 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. + +6.1. 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". -5.2. AS_PATH +6.2. AS_PATH - The error conditions for the attribute have been defined in - [RFC4271]. + 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". -5.3. NEXT_HOP + [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. - The error conditions for the NEXT_HOP attribute have been defined in - [RFC4271]. +6.3. NEXT_HOP + + The attribute is considered malformed if it is syntactically + incorrect according to [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 +6.4. MULTI_EXIT_DISC 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: +6.5. LOCAL_PREF - o using the approach of "attribute discard" if the UPDATE message is - received from an external neighbor, or + The error handling of [RFC4271] is revised as follows. - o using the approach of "treat-as-withdraw" if the UPDATE message is - received from an internal neighbor. + o If the LOCAL_PREF attribute is received from an external neighbor, + it SHALL be discarded using the approach of "attribute discard", + or - 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. + 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". -5.6. ATOMIC_AGGREGATE +6.6. 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 +6.7. 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". -5.8. Community +6.8. Community The error handling of [RFC1997] is revised as follows: The Community attribute SHALL be considered malformed if its length - is nonzero and is not a multiple of 4. + 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". -5.9. Extended Community +6.9. Extended Community The error handling of [RFC4360] is revised as follows: The Extended Community attribute SHALL be considered malformed if its - length is nonzero and is not a multiple of 8. + 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. -5.10. IPv6 Address Specific BGP Extended Community Attribute +6.10. 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. + 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. -5.11. ORIGINATOR_ID +6.11. 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". -5.12. CLUSTER_LIST +6.12. 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 multiple 4. If malformed, the - UPDATE SHALL be handled using the approach of "treat-as-withdraw". + 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". -6. IANA Considerations +6.13. MP_REACH_NLRI and MP_UNREACH_NLRI + + The handling of these attributes is discussed in Section 3 and + Section 4. + +7. 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 + account the tradeoff between preserving connectivity and potential + side effects. + +8. IANA Considerations This document makes no request of IANA. -7. Security Considerations +9. 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. Acknowledgements +10. Acknowledgements The authors wish to thank Juan Alcaide, Ron Bonica, Mach Chen, Andy - Davidson, Bruno Decraene, Rex Fernando, Jeff Haas, 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 and Lili Wang for their - observations and discussion of this topic, and review of this - document. + 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. -9. References +11. References -9.1. Normative References +11.1. 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 Protocol 4 (BGP-4)", RFC 4271, January 2006. @@ -565,26 +629,26 @@ "Multiprotocol Extensions for BGP-4", RFC 4760, January 2007. [RFC5701] Rekhter, Y., "IPv6 Address Specific BGP Extended Community Attribute", RFC 5701, November 2009. [RFC6793] Vohra, Q. and E. Chen, "BGP Support for Four-Octet Autonomous System (AS) Number Space", RFC 6793, December 2012. -9.2. Informative References +11.2. 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-06 (work in progress), March 2014. + evpn-07 (work in progress), May 2014. [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.