draft-ietf-idr-error-handling-19.txt   rfc7606.txt 
Internet Engineering Task Force E. Chen, Ed. Internet Engineering Task Force (IETF) E. Chen, Ed.
Internet-Draft Cisco Systems, Inc. Request for Comments: 7606 Cisco Systems, Inc.
Updates: 1997, 4271, 4360, 4456, 4760, J. Scudder, Ed. Updates: 1997, 4271, 4360, 4456, 4760, J. Scudder, Ed.
5543, 5701, 6368 (if approved) Juniper Networks 5543, 5701, 6368 Juniper Networks
Intended status: Standards Track P. Mohapatra Category: Standards Track P. Mohapatra
Expires: October 23, 2015 Sproute Networks ISSN: 2070-1721 Sproute Networks
K. Patel K. Patel
Cisco Systems, Inc. Cisco Systems, Inc.
April 21, 2015 August 2015
Revised Error Handling for BGP UPDATE Messages Revised Error Handling for BGP UPDATE Messages
draft-ietf-idr-error-handling-19
Abstract Abstract
According to the base BGP specification, a BGP speaker that receives According to the base BGP specification, a BGP speaker that receives
an UPDATE message containing a malformed attribute is required to an UPDATE message containing a malformed attribute is required to
reset the session over which the offending attribute was received. reset the session over which the offending attribute was received.
This behavior is undesirable, because a session reset would impact This behavior is undesirable because a session reset would impact not
not only routes with the offending attribute, but also other, valid only routes with the offending attribute but also other valid routes
routes exchanged over the session. This document partially revises exchanged over the session. This document partially revises the
the error handling for UPDATE messages and provides guidelines for error handling for UPDATE messages and provides guidelines for the
the authors of documents defining new attributes. Finally, it authors of documents defining new attributes. Finally, it revises
revises the error handling procedures for a number of existing the error handling procedures for a number of existing attributes.
attributes.
This document updates error handling for RFCs 1997, 4271, 4360, 4456, This document updates error handling for RFCs 1997, 4271, 4360, 4456,
4760, 5543, 5701 and 6368. 4760, 5543, 5701, and 6368.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
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 This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
This Internet-Draft will expire on October 23, 2015. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7606.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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skipping to change at page 2, line 34 skipping to change at page 3, line 7
modifications of such material outside the IETF Standards Process. modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other it for publication as an RFC or to translate it into languages other
than English. than English.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Error-Handling Approaches . . . . . . . . . . . . . . . . . . 4 2. Error-Handling Approaches . . . . . . . . . . . . . . . . . . 5
3. Revision to BGP UPDATE Message Error Handling . . . . . . . . 4 3. Revision to BGP UPDATE Message Error Handling . . . . . . . . 5
4. Attribute Length Fields . . . . . . . . . . . . . . . . . . . 6 4. Attribute Length Fields . . . . . . . . . . . . . . . . . . . 7
5. Parsing of Network Layer Reachability Information (NLRI) 5. Parsing of Network Layer Reachability Information (NLRI)
Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.1. Encoding NLRI . . . . . . . . . . . . . . . . . . . . . . 7 5.1. Encoding NLRI . . . . . . . . . . . . . . . . . . . . . . 8
5.2. Missing NLRI . . . . . . . . . . . . . . . . . . . . . . 7 5.2. Missing NLRI . . . . . . . . . . . . . . . . . . . . . . 8
5.3. Syntactic Correctness of NLRI Fields . . . . . . . . . . 8 5.3. Syntactic Correctness of NLRI Fields . . . . . . . . . . 9
5.4. Typed NLRI . . . . . . . . . . . . . . . . . . . . . . . 8 5.4. Typed NLRI . . . . . . . . . . . . . . . . . . . . . . . 9
6. Operational Considerations . . . . . . . . . . . . . . . . . 9 6. Operational Considerations . . . . . . . . . . . . . . . . . 10
7. Error Handling Procedures for Existing Attributes . . . . . . 10 7. Error-Handling Procedures for Existing Attributes . . . . . . 11
7.1. ORIGIN . . . . . . . . . . . . . . . . . . . . . . . . . 10 7.1. ORIGIN . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.2. AS_PATH . . . . . . . . . . . . . . . . . . . . . . . . . 10 7.2. AS_PATH . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.3. NEXT_HOP . . . . . . . . . . . . . . . . . . . . . . . . 11 7.3. NEXT_HOP . . . . . . . . . . . . . . . . . . . . . . . . 12
7.4. MULTI_EXIT_DISC . . . . . . . . . . . . . . . . . . . . . 11 7.4. MULTI_EXIT_DISC . . . . . . . . . . . . . . . . . . . . . 12
7.5. LOCAL_PREF . . . . . . . . . . . . . . . . . . . . . . . 11 7.5. LOCAL_PREF . . . . . . . . . . . . . . . . . . . . . . . 12
7.6. ATOMIC_AGGREGATE . . . . . . . . . . . . . . . . . . . . 11 7.6. ATOMIC_AGGREGATE . . . . . . . . . . . . . . . . . . . . 12
7.7. AGGREGATOR . . . . . . . . . . . . . . . . . . . . . . . 12 7.7. AGGREGATOR . . . . . . . . . . . . . . . . . . . . . . . 13
7.8. Community . . . . . . . . . . . . . . . . . . . . . . . . 12 7.8. Community . . . . . . . . . . . . . . . . . . . . . . . . 13
7.9. ORIGINATOR_ID . . . . . . . . . . . . . . . . . . . . . . 12 7.9. ORIGINATOR_ID . . . . . . . . . . . . . . . . . . . . . . 13
7.10. CLUSTER_LIST . . . . . . . . . . . . . . . . . . . . . . 12 7.10. CLUSTER_LIST . . . . . . . . . . . . . . . . . . . . . . 13
7.11. MP_REACH_NLRI . . . . . . . . . . . . . . . . . . . . . . 13 7.11. MP_REACH_NLRI . . . . . . . . . . . . . . . . . . . . . . 14
7.12. MP_UNREACH_NLRI . . . . . . . . . . . . . . . . . . . . . 13 7.12. MP_UNREACH_NLRI . . . . . . . . . . . . . . . . . . . . . 14
7.13. Traffic Engineering path attribute . . . . . . . . . . . 13 7.13. Traffic Engineering Path Attribute . . . . . . . . . . . 14
7.14. Extended Community . . . . . . . . . . . . . . . . . . . 13 7.14. Extended Community . . . . . . . . . . . . . . . . . . . 14
7.15. IPv6 Address Specific BGP Extended Community Attribute . 14 7.15. IPv6 Address Specific BGP Extended Community Attribute . 15
7.16. ATTR_SET . . . . . . . . . . . . . . . . . . . . . . . . 14 7.16. ATTR_SET . . . . . . . . . . . . . . . . . . . . . . . . 15
8. Guidance for Authors of BGP Specifications . . . . . . . . . 14 8. Guidance for Authors of BGP Specifications . . . . . . . . . 15
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 9. Security Considerations . . . . . . . . . . . . . . . . . . . 16
10. Security Considerations . . . . . . . . . . . . . . . . . . . 15 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16 10.1. Normative References . . . . . . . . . . . . . . . . . . 17
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 16 10.2. Informative References . . . . . . . . . . . . . . . . . 18
12.1. Normative References . . . . . . . . . . . . . . . . . . 16 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 19
12.2. Informative References . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction 1. Introduction
According to the base BGP specification [RFC4271], a BGP speaker that According to the base BGP specification [RFC4271], a BGP speaker that
receives an UPDATE message containing a malformed attribute is receives an UPDATE message containing a malformed attribute is
required to reset the session over which the offending attribute was required to reset the session over which the offending attribute was
received. This behavior is undesirable, because a session reset received. This behavior is undesirable because a session reset
impacts not only routes with the offending attribute, but also other, impacts not only routes with the offending attribute but also other
valid routes exchanged over the session. In the case of optional valid routes exchanged over the session. In the case of optional
transitive attributes, the behavior is especially troublesome and may transitive attributes, the behavior is especially troublesome and may
present a potential security vulnerability. This is because present a potential security vulnerability. This is because
attributes may have been propagated without being checked by attributes may have been propagated without being checked by
intermediate routers that don't recognize the attributes. In effect, intermediate routers that don't recognize the attributes. In effect,
the attributes may have been tunneled; and when they reach a router the attributes may have been tunneled; when they reach a router that
that recognizes and checks the attributes, the session that is reset recognizes and checks the attributes, the session that is reset may
may not be associated with the router that is at fault. To make not be associated with the router that is at fault. To make matters
matters worse, in such cases although the problematic attributes may worse, in such cases, although the problematic attributes may have
have originated with a single update transmitted by a single BGP originated with a single update transmitted by a single BGP speaker,
speaker, by the time they encounter a router that checks them they by the time they encounter a router that checks them they may have
may have been replicated many times, and thus may cause the reset of been replicated many times and thus may cause the reset of many
many peering sessions. Thus the damage inflicted may be multiplied peering sessions. Thus, the damage inflicted may be multiplied
manyfold. manyfold.
The goal for revising the error handling for UPDATE messages is to The goal for revising the error handling for UPDATE messages is to
minimize the impact on routing by a malformed UPDATE message, while minimize the impact on routing by a malformed UPDATE message while
maintaining protocol correctness to the extent possible. This can be maintaining protocol correctness to the extent possible. This can be
achieved largely by maintaining the established session and keeping achieved largely by maintaining the established session and keeping
the valid routes exchanged, but removing the routes carried in the the valid routes exchanged but removing the routes carried in the
malformed UPDATE from the routing system. malformed UPDATE message from the routing system.
This document partially revises the error handling for UPDATE This document partially revises the error handling for UPDATE
messages, and provides guidelines for the authors of documents messages and provides guidelines for the authors of documents
defining new attributes. Finally, it revises the error handling defining new attributes. Finally, it revises the error handling
procedures for a number of existing attributes. Specifically, the 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], [RFC5543], [RFC5701], and [RFC6368] are [RFC4456], [RFC4760], [RFC5543], [RFC5701], and [RFC6368] are
revised. revised.
1.1. Requirements Language 1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
2. Error-Handling Approaches 2. Error-Handling Approaches
In this document we refer to four different approaches to handle In this document, we refer to four different approaches to handle
errors found in BGP path attributes. They are as follows (listed in errors found in a BGP UPDATE message. They are as follows (listed in
order, from the one with the "strongest" action to the one with the order, from the one with the "strongest" action to the one with the
"weakest" action): "weakest" action):
o Session reset: This is the approach used throughout the base BGP o Session reset: This is the approach used throughout the base BGP
specification [RFC4271], where a NOTIFICATION is sent and the specification [RFC4271], where a NOTIFICATION is sent and the
session terminated. session terminated.
o AFI/SAFI disable: [RFC4760] specifies a procedure for disabling a o AFI/SAFI disable: Section 7 of [RFC4760] allows a BGP speaker that
particular AFI/SAFI (Address Family Identifier and Subsequent detects an error in a message for a given AFI/SAFI to optionally
Address Family Identifier). "ignore all the subsequent routes with that AFI/SAFI received over
that session". We refer to this as "disabling a particular AFI/
SAFI" or "AFI/SAFI disable".
o Treat-as-withdraw: In this approach, the UPDATE message containing o Treat-as-withdraw: In this approach, the UPDATE message containing
the path attribute in question MUST be treated as though all the path attribute in question MUST be treated as though all
contained routes had been withdrawn just as if they had been contained routes had been withdrawn just as if they had been
listed in the WITHDRAWN ROUTES field (or in the MP_UNREACH_NLRI listed in the WITHDRAWN ROUTES field (or in the MP_UNREACH_NLRI
attribute if appropriate) of the UPDATE message, thus causing them attribute if appropriate) of the UPDATE message, thus causing them
to be removed from the Adj-RIB-In according to the procedures of to be removed from the Adj-RIB-In according to the procedures of
[RFC4271]. [RFC4271].
o Attribute discard: In this approach the malformed attribute MUST o Attribute discard: In this approach, the malformed attribute MUST
be discarded and the UPDATE message continues to be processed. be discarded and the UPDATE message continues to be processed.
This approach MUST NOT be used except in the case of an attribute This approach MUST NOT be used except in the case of an attribute
that has no effect on route selection or installation. that has no effect on route selection or installation.
3. Revision to BGP UPDATE Message Error Handling 3. Revision to BGP UPDATE Message Error Handling
This specification amends [RFC4271] Section 6.3 in a number of ways. This specification amends Section 6.3 of [RFC4271] in a number of
See also Section 7 for treatment of specific path attributes. ways. See Section 7 for treatment of specific path attributes.
a. The first paragraph is revised as follows: a. The first paragraph is revised as follows:
Old Text: Old Text:
All errors detected while processing the UPDATE message All errors detected while processing the UPDATE message
MUST be indicated by sending the NOTIFICATION message with MUST be indicated by sending the NOTIFICATION message with
the Error Code UPDATE Message Error. The error subcode the Error Code UPDATE Message Error. The error subcode
elaborates on the specific nature of the error. elaborates on the specific nature of the error.
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conflict with the Attribute Type Code, then the Error conflict with the Attribute Type Code, then the Error
Subcode MUST be set to Attribute Flags Error. The Data Subcode MUST be set to Attribute Flags Error. The Data
field MUST contain the erroneous attribute (type, length, field MUST contain the erroneous attribute (type, length,
and value). and value).
New Text: New Text:
If the value of either the Optional or Transitive bits in If the value of either the Optional or Transitive bits in
the Attribute Flags is in conflict with their specified the Attribute Flags is in conflict with their specified
values, then the attribute MUST be treated as malformed and values, then the attribute MUST be treated as malformed and
the treat-as-withdraw approach used, unless the the "treat-as-withdraw" approach used, unless the
specification for the attribute mandates different handling specification for the attribute mandates different handling
for incorrect Attribute Flags. for incorrect Attribute Flags.
d. If any of the well-known mandatory attributes are not present in d. If any of the well-known mandatory attributes are not present in
an UPDATE message, then "treat-as-withdraw" MUST be used. (Note an UPDATE message, then "treat-as-withdraw" MUST be used. (Note
that [RFC4760] reclassifies NEXT_HOP as what is effectively that [RFC4760] reclassifies NEXT_HOP as what is effectively
discretionary.) discretionary.)
e. "Treat-as-withdraw" MUST be used for the cases that specify a e. "Treat-as-withdraw" MUST be used for the cases that specify a
session reset and involve any of the attributes ORIGIN, AS_PATH, session reset and involve any of the attributes ORIGIN, AS_PATH,
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f. "Attribute discard" MUST be used for any of the cases that f. "Attribute discard" MUST be used for any of the cases that
specify a session reset and involve ATOMIC_AGGREGATE or specify a session reset and involve ATOMIC_AGGREGATE or
AGGREGATOR. AGGREGATOR.
g. If the MP_REACH_NLRI attribute or the MP_UNREACH_NLRI [RFC4760] g. If the MP_REACH_NLRI attribute or the MP_UNREACH_NLRI [RFC4760]
attribute appears more than once in the UPDATE message, then a attribute appears more than once in the UPDATE message, then a
NOTIFICATION message MUST be sent with the Error Subcode NOTIFICATION message MUST be sent with the Error Subcode
"Malformed Attribute List". If any other attribute (whether "Malformed Attribute List". If any other attribute (whether
recognized or unrecognized) appears more than once in an UPDATE recognized or unrecognized) appears more than once in an UPDATE
message, then all the occurrences of the attribute other than the message, then all the occurrences of the attribute other than the
first one SHALL be discarded and the UPDATE message continue to first one SHALL be discarded and the UPDATE message will continue
be processed. to be processed.
h. When multiple attribute errors exist in an UPDATE message, if the h. When multiple attribute errors exist in an UPDATE message, if the
same approach (either "session reset", "treat-as-withdraw" or same approach (as described in Section 2) is specified for the
"attribute discard") is specified for the handling of these handling of these malformed attributes, then the specified
malformed attributes, then the specified approach MUST be used. approach MUST be used. Otherwise, the approach with the
Otherwise the approach with the strongest action MUST be used. strongest action MUST be used.
i. The Withdrawn Routes field MUST be checked for syntactic i. The Withdrawn Routes field MUST be checked for syntactic
correctness in the same manner as the NLRI (network layer correctness in the same manner as the NLRI field. This is
reachability information) field. This is discussed further discussed further below and in Section 5.3.
below, and in Section 5.3.
j. Finally, we observe that in order to use the approach of "treat- 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 as-withdraw", the entire NLRI field and/or the MP_REACH_NLRI and
MP_UNREACH_NLRI attributes need to be successfully parsed -- what MP_UNREACH_NLRI attributes need to be successfully parsed -- what
this entails is discussed in more detail in Section 5. If this this entails is discussed in more detail in Section 5. If this
is not possible, the procedures of [RFC4271] and/or [RFC4760] is not possible, the procedures of [RFC4271] and/or [RFC4760]
continue to apply, meaning that the "session reset" approach (or continue to apply, meaning that the "session reset" approach (or
the "AFI/SAFI disable" approach) MUST be followed. the "AFI/SAFI disable" approach) MUST be followed.
4. Attribute Length Fields 4. Attribute Length Fields
There are two error cases in which the Total Attribute Length value There are two error cases in which the Total Attribute Length value
can be in conflict with the enclosed path attributes, which can be in conflict with the enclosed path attributes, which
themselves carry length values. In the "overrun" case, as the themselves carry length values:
enclosed path attributes are parsed, the length of the last
encountered path attribute would cause the Total Attribute Length to o In the first case, the length of the last encountered path
be exceeded. In the "underrun" case, as the enclosed path attributes attribute would cause the Total Attribute Length to be exceeded
are parsed, after the last successfully-parsed attribute, fewer than when parsing the enclosed path attributes.
three octets remain, or fewer than four octets, if the Attribute
Flags field has the Extended Length bit set -- that is, there remains o In the second case, fewer than three octets remain (or fewer than
unconsumed data in the path attributes but yet insufficient data to four octets, if the Attribute Flags field has the Extended Length
encode a single minimum-sized path attribute. In either of these bit set) when beginning to parse the attribute. That is, this
cases, an error condition exists and the treat-as-withdraw approach case exists if there remains unconsumed data in the path
MUST be used (unless some other, more severe error is encountered attributes but yet insufficient data to encode a single minimum-
dictating a stronger approach), and the Total Attribute Length MUST sized path attribute.
be relied upon to enable the beginning of the NLRI field to be
located. 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.
For all path attributes other than those specified as having an For all path attributes other than those specified as having an
attribute length that may be zero, it SHALL be considered a syntax 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 error for the attribute to have a length of zero. Of the path
attributes considered in this specification, only AS_PATH and attributes considered in this specification, only AS_PATH and
ATOMIC_AGGREGATE may validly have an attribute length of zero.) ATOMIC_AGGREGATE may validly have an attribute length of zero.
5. Parsing of Network Layer Reachability Information (NLRI) Fields 5. Parsing of Network Layer Reachability Information (NLRI) Fields
5.1. Encoding NLRI 5.1. Encoding NLRI
To facilitate the determination of the NLRI field in an UPDATE with a To facilitate the determination of the NLRI field in an UPDATE
malformed attribute: message with a malformed attribute:
o The MP_REACH_NLRI or MP_UNREACH_NLRI attribute (if present) SHALL o The MP_REACH_NLRI or MP_UNREACH_NLRI attribute (if present) SHALL
be encoded as the very first path attribute in an UPDATE. be encoded as the very first path attribute in an UPDATE message.
o An UPDATE message MUST NOT contain more than one of the following: o An UPDATE message MUST NOT contain more than one of the following:
non-empty Withdrawn Routes field, non-empty Network Layer non-empty Withdrawn Routes field, non-empty Network Layer
Reachability Information field, MP_REACH_NLRI attribute, and Reachability Information field, MP_REACH_NLRI attribute, and
MP_UNREACH_NLRI attribute. MP_UNREACH_NLRI attribute.
Since older BGP speakers may not implement these restrictions, an Since older BGP speakers may not implement these restrictions, an
implementation MUST still be prepared to receive these fields in any implementation MUST still be prepared to receive these fields in any
position or combination. position or combination.
If the encoding of [RFC4271] is used, the NLRI field for the IPv4 If the encoding of [RFC4271] is used, the NLRI field for the IPv4
unicast address family is carried immediately following all the unicast address family is carried immediately following all the
attributes in an UPDATE. When such an UPDATE is received, we observe attributes in an UPDATE message. When such an UPDATE message is
that the NLRI field can be determined using the "Message Length", received, we observe that the NLRI field can be determined using the
"Withdrawn Route Length" and "Total Attribute Length" (when they are Message Length, Withdrawn Route Length, and Total Attribute Length
consistent) carried in the message instead of relying on the length (when they are consistent) carried in the message instead of relying
of individual attributes in the message. on the length of individual attributes in the message.
5.2. Missing NLRI 5.2. Missing NLRI
[RFC4724] specifies an End-of-RIB message ("EoR") that can be encoded [RFC4724] specifies an End-of-RIB message (EoR) that can be encoded
as an UPDATE message that contains only a MP_UNREACH_NLRI attribute as an UPDATE message that contains only a MP_UNREACH_NLRI attribute
that encodes no NLRI (it can also be a completely empty UPDATE that encodes no NLRI (it can also be a completely empty UPDATE
message in the case of the "legacy" encoding). In all other well- message in the case of the "legacy" encoding). In all other well-
specified cases, an UPDATE either carries only withdrawn routes specified cases, an UPDATE message either carries only withdrawn
(either in the Withdrawn Routes field, or the MP_UNREACH_NLRI routes (either in the Withdrawn Routes field or the MP_UNREACH_NLRI
attribute), or it advertises reachable routes (either in the Network attribute) or it advertises reachable routes (either in the Network
Layer Reachability Information field, or the MP_REACH_NLRI Layer Reachability Information field or the MP_REACH_NLRI attribute).
attribute).
Thus, if an UPDATE message is encountered that does contain path Thus, if an UPDATE message is encountered that does contain path
attributes other than MP_UNREACH_NLRI and doesn't encode any attributes other than MP_UNREACH_NLRI and doesn't encode any
reachable NLRI, we cannot be confident that the NLRI have been reachable NLRI, we cannot be confident that the NLRI have been
successfully parsed as Section 3 (j) requires. For this reason, if successfully parsed as Section 3 (j) requires. For this reason, if
any path attribute errors are encountered in such an UPDATE message, any path attribute errors are encountered in such an UPDATE message
and if any encountered error specifies an error-handling approach and if any encountered error specifies an error-handling approach
other than "attribute discard", then the "session reset" approach other than "attribute discard", then the "session reset" approach
MUST be used. MUST be used.
5.3. Syntactic Correctness of NLRI Fields 5.3. Syntactic Correctness of NLRI Fields
The NLRI field or Withdrawn Routes field SHALL be considered The NLRI field or Withdrawn Routes field SHALL be considered
"syntactically incorrect" if either of the following are true: "syntactically incorrect" if either of the following are true:
o The length of any of the included NLRI is greater than 32, 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 o When parsing NLRI contained in the field, the length of the last
NLRI found exceeds the amount of unconsumed data remaining in the NLRI found exceeds the amount of unconsumed data remaining in the
field. field.
Similarly, the MP_REACH_NLRI or MP_UNREACH_NLRI attribute of an Similarly, the MP_REACH_NLRI or MP_UNREACH_NLRI attribute of an
update SHALL be considered to be incorrect if any of the following update SHALL be considered to be incorrect if any of the following
are true: are true:
o The length of any of the included NLRI is inconsistent with the 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 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), than 32 or an IPv6 NLRI has a length greater than 128).
o When parsing NLRI contained in the attribute, the length of the o When parsing NLRI contained in the attribute, the length of the
last NLRI found exceeds the amount of unconsumed data remaining in last NLRI found exceeds the amount of unconsumed data remaining in
the attribute. the attribute.
o The attribute flags of the attribute are inconsistent with those o The attribute flags of the attribute are inconsistent with those
specified in [RFC4760]. specified in [RFC4760].
o The length of the MP_UNREACH_NLRI attribute is less than 3, or the 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. length of the MP_REACH_NLRI attribute is less than 5.
5.4. Typed NLRI 5.4. Typed NLRI
Certain address families, for example MCAST-VPN [RFC6514], MCAST-VPLS Certain address families, for example, MCAST-VPN [RFC6514], MCAST-
[RFC7117] and EVPN [RFC7432] have NLRI that are typed. Since VPLS [RFC7117], and EVPN [RFC7432] have NLRI that are typed. Since
supported type values within the address family are not expressed in supported type values within the address family are not expressed in
the MP-BGP capability [RFC4760], it is possible for a BGP speaker to the Multiprotocol BGP (MP-BGP) capability [RFC4760], it is possible
advertise support for the given address family and sub-address family for a BGP speaker to advertise support for the given address family
while still not supporting a particular type of NLRI within that AFI/ and subaddress family while still not supporting a particular type of
SAFI. NLRI within that AFI/SAFI.
A BGP speaker advertising support for such a typed address family A BGP speaker advertising support for such a typed address family
MUST handle routes with unrecognized NLRI types within that address MUST handle routes with unrecognized NLRI types within that address
family by discarding them, unless the relevant specification for that family by discarding them, unless the relevant specification for that
address family specifies otherwise. address family specifies otherwise.
6. Operational Considerations 6. Operational Considerations
Although the "treat-as-withdraw" error-handling behavior defined in Although the "treat-as-withdraw" error-handling behavior defined in
Section 2 makes every effort to preserve BGP's correctness, we note 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 that if an UPDATE message received on an Internal BGP (IBGP) session
treatment, inconsistent routing within the affected Autonomous System is subjected to this treatment, inconsistent routing within the
may result. The consequences of inconsistent routing can include affected Autonomous System may result. The consequences of
long-lived forwarding loops and black holes. While lamentable, this inconsistent routing can include long-lived forwarding loops and
issue is expected to be rare in practice, and, more importantly, is black holes. While lamentable, this issue is expected to be rare in
seen as less problematic than the session-reset behavior it replaces. 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, When a malformed attribute is indeed detected over an IBGP session,
we recommend that routes with the malformed attribute be identified we recommend that routes with the malformed attribute be identified
and traced back to the ingress router in the network where the routes 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 were sourced or received externally and then a filter be applied on
the ingress router to prevent the routes from being sourced or the ingress router to prevent the routes from being sourced or
received. This will help maintain routing consistency in the received. This will help maintain routing consistency in the
network. network.
Even if inconsistent routing does not arise, the "treat-as-withdraw" Even if inconsistent routing does not arise, the "treat-as-withdraw"
behavior can cause either complete unreachability or sub-optimal behavior can cause either complete unreachability or suboptimal
routing for the destinations whose routes are carried in the affected routing for the destinations whose routes are carried in the affected
UPDATE message. UPDATE message.
Note that "treat-as-withdraw" is different from discarding an UPDATE Note that "treat-as-withdraw" is different from discarding an UPDATE
message. The latter violates the basic BGP principle of incremental message. The latter violates the basic BGP principle of an
update, and could cause invalid routes to be kept. incremental update and could cause invalid routes to be kept.
Because of these potential issues, a BGP speaker must provide Because of these potential issues, a BGP speaker must provide
debugging facilities to permit issues caused by a malformed attribute debugging facilities to permit issues caused by a malformed attribute
to be diagnosed. At a minimum, such facilities must include logging to be diagnosed. At a minimum, such facilities must include logging
an error listing the NLRI involved, and containing the entire an error listing the NLRI involved and containing the entire
malformed UPDATE message when such an attribute is detected. The malformed UPDATE message when such an attribute is detected. The
malformed UPDATE message should be analyzed, and the root cause malformed UPDATE message should be analyzed, and the root cause
should be investigated. should be investigated.
Section 8 mentions that attribute discard should not be used in cases Section 8 mentions that "attribute discard" should not be used in
where "the attribute in question has or may have an effect on route cases where "the attribute in question has or may have an effect on
selection." Although all cases that specify attribute discard in route selection." Although all cases that specify "attribute
this document do not affect route selection by default, in principle discard" in this document do not affect route selection by default,
routing policies could be written that affect selection based on such in principle, routing policies could be written that affect selection
an attribute. Operators should take care when writing such policies based on such an attribute. Operators should take care when writing
to consider the possible consequences of an attribute discard. (In such policies to consider the possible consequences of an attribute
general, as long as such policies are only applied to external BGP discard. In general, as long as such policies are only applied to
sessions, correctness issues are not expected to arise.) external BGP sessions, correctness issues are not expected to arise.
7. Error Handling Procedures for Existing Attributes 7. Error-Handling Procedures for Existing Attributes
In the following subsections, we elaborate on the conditions for In the following subsections, we elaborate on the conditions for
error-checking various path attributes, and specify what approach(es) error-checking various path attributes and specify what approach(es)
should be used to handle malformations. It is possible that should be used to handle malformations. It is possible that
implementations may apply other error checks not contemplated here. implementations may apply other error checks not contemplated here.
If so, the error handling approach given here should generally be If so, the error handling approach given here should generally be
applied. applied.
This section addresses all path attributes that are defined at the This section addresses all path attributes that are defined at the
time of this writing, that were not defined with error-handling time of this writing that were not defined with error handling
consistent with Section 8, and that are not marked as "deprecated" in consistent with Section 8 and that are not marked as "deprecated" in
[IANA-BGP-ATTRS]. Attributes 17 (AS4_PATH), 18 (AS4_AGGREGATOR), 22 the "BGP Path Attributes" registry [IANA-BGP-ATTRS]. Attributes 17
(PMSI_TUNNEL), 23 (Tunnel Encapsulation Attribute), 26 (AIGP), 27 (PE (AS4_PATH), 18 (AS4_AGGREGATOR), 22 (PMSI_TUNNEL), 23 (Tunnel
Distinguisher Labels) and 29 (BGP-LS Attribute) do have error- Encapsulation Attribute), 26 (AIGP), 27 (PE Distinguisher Labels),
handling consistent with Section 8 and thus are not further discussed and 29 (BGP-LS Attribute) do have error handling consistent with
herein. Attributes 11 (DPA), 12 (ADVERTISER), 13 (RCID_PATH / Section 8 and thus are not further discussed herein. Attributes 11
CLUSTER_ID), 19 (SAFI Specific Attribute), 20 (Connector Attribute), (DPA), 12 (ADVERTISER), 13 (RCID_PATH / CLUSTER_ID), 19 (SAFI
21 (AS_PATHLIMIT) and 28 (BGP Entropy Label Capability Attribute) are Specific Attribute), 20 (Connector Attribute), 21 (AS_PATHLIMIT), and
deprecated and thus are not further discussed herein. 28 (BGP Entropy Label Capability Attribute) are deprecated and thus
are not further discussed herein.
7.1. ORIGIN 7.1. ORIGIN
The attribute is considered malformed if its length is not 1, or it The attribute is considered malformed if its length is not 1 or if it
has an undefined value [RFC4271]. has an undefined value [RFC4271].
An UPDATE message with a malformed ORIGIN attribute SHALL be handled An UPDATE message with a malformed ORIGIN attribute SHALL be handled
using the approach of "treat-as-withdraw". using the approach of "treat-as-withdraw".
7.2. AS_PATH 7.2. AS_PATH
An AS_PATH is considered malformed if an unrecognized segment type is An AS_PATH is considered malformed if an unrecognized segment type is
encountered, or if it contains a malformed segment. A segment is encountered or if it contains a malformed segment. A segment is
considered malformed if any of the following obtains: considered malformed if any of the following are true:
o There is an overrun, where the path segment length field of the o There is an overrun where the Path Segment Length field of the
last segment encountered would cause the Attribute Length to be last segment encountered would cause the Attribute Length to be
exceeded. exceeded.
o There is an underrun, where after the last successfully-parsed o There is an underrun where after the last successfully parsed
segment, there is only a single octet remaining (that is, there is segment there is only a single octet remaining (that is, there is
not enough unconsumed data to provide even an empty segment not enough unconsumed data to provide even an empty segment
header). header).
o It has a path segment length field of zero. o It has a Path Segment Length field of zero.
An UPDATE message with a malformed AS_PATH attribute SHALL be handled An UPDATE message with a malformed AS_PATH attribute SHALL be handled
using the approach of "treat-as-withdraw". using the approach of "treat-as-withdraw".
[RFC4271] also says that an implementation optionally "MAY check [RFC4271] also says that an implementation optionally "MAY check
whether the leftmost ... AS in the AS_PATH attribute is equal to the 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 autonomous system number of the peer that sent the message". A BGP
implementation SHOULD also handle routes that violate this check implementation SHOULD also handle routes that violate this check
using "treat-as-withdraw", but MAY follow the session reset behavior using "treat-as-withdraw" but MAY follow the "session reset" behavior
if configured to do so. if configured to do so.
7.3. NEXT_HOP 7.3. NEXT_HOP
The attribute is considered malformed if its length is not 4 The attribute is considered malformed if its length is not 4
[RFC4271]. [RFC4271].
An UPDATE message with a malformed NEXT_HOP attribute SHALL be An UPDATE message with a malformed NEXT_HOP attribute SHALL be
handled using the approach of "treat-as-withdraw". handled using the approach of "treat-as-withdraw".
7.4. MULTI_EXIT_DISC 7.4. MULTI_EXIT_DISC
The attribute is considered malformed if its length is not 4 The attribute is considered malformed if its length is not 4
[RFC4271]. [RFC4271].
An UPDATE message with a malformed MULTI_EXIT_DISC attribute SHALL be An UPDATE message with a malformed MULTI_EXIT_DISC attribute SHALL be
handled using the approach of "treat-as-withdraw". handled using the approach of "treat-as-withdraw".
7.5. LOCAL_PREF 7.5. LOCAL_PREF
The error handling of [RFC4271] is revised as follows. The error handling of [RFC4271] is revised as follows:
o If the LOCAL_PREF attribute is received from an external neighbor, o if the LOCAL_PREF attribute is received from an external neighbor,
it SHALL be discarded using the approach of "attribute discard", it SHALL be discarded using the approach of "attribute discard";
or or
o if received from an internal neighbor, it SHALL be considered o if received from an internal neighbor, it SHALL be considered
malformed if its length is not equal to 4. If malformed, the malformed if its length is not equal to 4. If malformed, the
UPDATE SHALL be handled using the approach of "treat-as-withdraw". UPDATE message SHALL be handled using the approach of "treat-as-
withdraw".
7.6. ATOMIC_AGGREGATE 7.6. ATOMIC_AGGREGATE
The attribute SHALL be considered malformed if its length is not 0 The attribute SHALL be considered malformed if its length is not 0
[RFC4271]. [RFC4271].
An UPDATE message with a malformed ATOMIC_AGGREGATE attribute SHALL An UPDATE message with a malformed ATOMIC_AGGREGATE attribute SHALL
be handled using the approach of "attribute discard". be handled using the approach of "attribute discard".
7.7. AGGREGATOR 7.7. AGGREGATOR
The error conditions specified in [RFC4271] for the attribute are The error conditions specified in [RFC4271] for the attribute are
revised as follows: revised as follows:
The AGGREGATOR attribute SHALL be considered malformed if any of the The AGGREGATOR attribute SHALL be considered malformed if any of the
following applies: following applies:
o Its length is not 6 (when the "4-octet AS number capability" is o Its length is not 6 (when the 4-octet AS number capability is not
not advertised to, or not received from the peer [RFC6793]). advertised to or not received from the peer [RFC6793]).
o Its length is not 8 (when the "4-octet AS number capability" is o Its length is not 8 (when the 4-octet AS number capability is both
both advertised to, and received from the peer). advertised to and received from the peer).
An UPDATE message with a malformed AGGREGATOR attribute SHALL be An UPDATE message with a malformed AGGREGATOR attribute SHALL be
handled using the approach of "attribute discard". handled using the approach of "attribute discard".
7.8. Community 7.8. Community
The error handling of [RFC1997] is revised as follows: The error handling of [RFC1997] is revised as follows:
The Community attribute SHALL be considered malformed if its length o The Community attribute SHALL be considered malformed if its
is not a nonzero multiple of 4. length is not a non-zero multiple of 4.
An UPDATE message with a malformed Community attribute SHALL be o An UPDATE message with a malformed Community attribute SHALL be
handled using the approach of "treat-as-withdraw". handled using the approach of "treat-as-withdraw".
7.9. ORIGINATOR_ID 7.9. ORIGINATOR_ID
The error handling of [RFC4456] is revised as follows. The error handling of [RFC4456] is revised as follows:
o If the ORIGINATOR_ID attribute is received from an external o if the ORIGINATOR_ID attribute is received from an external
neighbor, it SHALL be discarded using the approach of "attribute neighbor, it SHALL be discarded using the approach of "attribute
discard", or discard"; or
o if received from an internal neighbor, it SHALL be considered o if received from an internal neighbor, it SHALL be considered
malformed if its length is not equal to 4. If malformed, the malformed if its length is not equal to 4. If malformed, the
UPDATE SHALL be handled using the approach of "treat-as-withdraw". UPDATE message SHALL be handled using the approach of "treat-as-
withdraw".
7.10. CLUSTER_LIST 7.10. CLUSTER_LIST
The error handling of [RFC4456] is revised as follows. The error handling of [RFC4456] is revised as follows:
o If the CLUSTER_LIST attribute is received from an external o if the CLUSTER_LIST attribute is received from an external
neighbor, it SHALL be discarded using the approach of "attribute neighbor, it SHALL be discarded using the approach of "attribute
discard", or discard"; or
o if received from an internal neighbor, it SHALL be considered o if received from an internal neighbor, it SHALL be considered
malformed if its length is not a nonzero multiple of 4. If malformed if its length is not a non-zero multiple of 4. If
malformed, the UPDATE SHALL be handled using the approach of malformed, the UPDATE message SHALL be handled using the approach
"treat-as-withdraw". of "treat-as-withdraw".
7.11. MP_REACH_NLRI 7.11. MP_REACH_NLRI
If the Length of Next Hop Network Address field of the MP_REACH If the Length of Next Hop Network Address field of the MP_REACH
attribute is inconsistent with that which was expected, the attribute attribute is inconsistent with that which was expected, the attribute
is considered malformed. Since the next hop precedes the NLRI field is considered malformed. Since the next hop precedes the NLRI field
in the attribute, in this case it will not be possible to reliably in the attribute, in this case it will not be possible to reliably
locate the NLRI, and thus the "session reset" or "AFI/SAFI disable" locate the NLRI; thus, the "session reset" or "AFI/SAFI disable"
approach MUST be used. approach MUST be used.
"That which was expected", while somewhat vague, is intended to "That which was expected", while somewhat vague, is intended to
encompass the next hop specified for the Address Family Identifier encompass the next hop specified for the Address Family Identifier
and Subsequent Address Family Identifier fields and potentially and Subsequent Address Family Identifier fields and is potentially
modified by any extensions in use. For example, if [RFC5549] is in modified by any extensions in use. For example, if [RFC5549] is in
use then the next hop would have to have a length of 4 or 16. use, then the next hop would have to have a length of 4 or 16.
Section 3 and Section 5 provide further discussion of the handling of Sections 3 and 5 provide further discussion of the handling of this
this attribute. attribute.
7.12. MP_UNREACH_NLRI 7.12. MP_UNREACH_NLRI
Section 3 and Section 5 discuss the handling of this attribute. Sections 3 and 5 discuss the handling of this attribute.
7.13. Traffic Engineering path attribute 7.13. Traffic Engineering Path Attribute
We note that [RFC5543] does not detail what constitutes We note that [RFC5543] does not detail what constitutes
"malformation" for the Traffic Engineering path attribute. A future "malformation" for the Traffic Engineering path attribute. A future
update to that specification may provide more guidance. In the update to that specification may provide more guidance. In the
interim, an implementation that determines (for whatever reason) that interim, an implementation that determines (for whatever reason) that
an UPDATE message contains a malformed Traffic Engineering path an UPDATE message contains a malformed Traffic Engineering path
attribute MUST handle it using the approach of "treat-as-withdraw". attribute MUST handle it using the approach of "treat-as-withdraw".
7.14. Extended Community 7.14. Extended Community
The error handling of [RFC4360] is revised as follows: The error handling of [RFC4360] is revised as follows:
The Extended Community attribute SHALL be considered malformed if its o The Extended Community attribute SHALL be considered malformed if
length is not a nonzero multiple of 8. its length is not a non-zero multiple of 8.
An UPDATE message with a malformed Extended Community attribute SHALL o An UPDATE message with a malformed Extended Community attribute
be handled using the approach of "treat-as-withdraw". SHALL be handled using the approach of "treat-as-withdraw".
Note that a BGP speaker MUST NOT treat an unrecognized Extended Note that a BGP speaker MUST NOT treat an unrecognized Extended
Community Type or Sub-Type as an error. Community Type or Sub-Type as an error.
7.15. IPv6 Address Specific BGP Extended Community Attribute 7.15. IPv6 Address Specific BGP Extended Community Attribute
The error handling of [RFC5701] is revised as follows: The error handling of [RFC5701] is revised as follows:
The IPv6 Address Specific Extended Community attribute SHALL be o The IPv6 Address Specific Extended Community attribute SHALL be
considered malformed if its length is not a nonzero multiple of 20. considered malformed if its length is not a non-zero multiple of
20.
An UPDATE message with a malformed IPv6 Address Specific Extended o An UPDATE message with a malformed IPv6 Address Specific Extended
Community attribute SHALL be handled using the approach of "treat-as- Community attribute SHALL be handled using the approach of "treat-
withdraw". as-withdraw".
Note that a BGP speaker MUST NOT treat an unrecognized IPv6 Address Note that a BGP speaker MUST NOT treat an unrecognized IPv6 Address
Specific Extended Community Type or Sub-Type as an error. Specific Extended Community Type or Sub-Type as an error.
7.16. ATTR_SET 7.16. ATTR_SET
The final paragraph of Section 5 of [RFC6368] is revised as follows: The final paragraph of Section 5 of [RFC6368] is revised as follows:
Old Text: Old Text:
An UPDATE message with a malformed ATTR_SET attribute SHALL be An UPDATE message with a malformed ATTR_SET attribute SHALL be
handled as follows. If its Partial flag is set and its handled as follows. If its Partial flag is set and its
Neighbor-Complete flag is clear, the UPDATE is treated as a Neighbor-Complete flag is clear, the UPDATE message is treated
route withdraw as discussed in [OPT-TRANS-BGP]. Otherwise as a route withdraw as discussed in [OPT-TRANS-BGP]. Otherwise
(i.e., Partial flag is clear or Neighbor-Complete is set), the (i.e., Partial flag is clear or Neighbor-Complete is set), the
procedures of the BGP-4 base specification [RFC4271] MUST be procedures of the BGP-4 base specification [RFC4271] MUST be
followed with respect to an Optional Attribute Error. followed with respect to an Optional Attribute Error.
New Text: New Text:
An UPDATE message with a malformed ATTR_SET attribute SHALL be An UPDATE message with a malformed ATTR_SET attribute SHALL be
handled using the approach of "treat as withdraw". handled using the approach of "treat as withdraw".
Furthermore, the normative reference to [OPT-TRANS-BGP] in [RFC6368] Furthermore, the normative reference to [OPT-TRANS-BGP] in [RFC6368]
is removed. is removed.
8. Guidance for Authors of BGP Specifications 8. Guidance for Authors of BGP Specifications
A document that specifies a new BGP attribute MUST provide specifics A document that specifies a new BGP attribute MUST provide specifics
regarding what constitutes an error for that attribute and how that regarding what constitutes an error for that attribute and how that
error is to be handled. Allowable error-handling approaches are error is to be handled. Allowable error-handling approaches are
detailed in Section 2. The treat-as-withdraw approach is generally detailed in Section 2. The "treat-as-withdraw" approach is generally
preferred. The document SHOULD also provide consideration of what preferred and the "session reset" approach is discouraged. Authors
debugging facilities may be required to permit issues caused by a of BGP documents are also reminded to review the discussion of
malformed attribute to be diagnosed. optional transitive attributes in the first paragraph of the
Introduction of this document. 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 For any malformed attribute that is handled by the "attribute
discard" instead of the "treat-as-withdraw" approach, it is critical discard" instead of the "treat-as-withdraw" approach, it is critical
to consider the potential impact of doing so. In particular, if the 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 attribute in question has or may have an effect on route selection or
installation, the presumption is that discarding it is unsafe, unless installation, the presumption is that discarding it is unsafe unless
careful analysis proves otherwise. The analysis should take into careful analysis proves otherwise. The analysis should take into
account the tradeoff between preserving connectivity and potential account the tradeoff between preserving connectivity and potential
side effects. side effects.
Authors can refer to Section 7 for examples. Authors can refer to Section 7 for examples.
9. IANA Considerations 9. Security Considerations
This document makes no request of IANA.
10. Security Considerations
This specification addresses the vulnerability of a BGP speaker to a This specification addresses the vulnerability of a BGP speaker to a
potential attack whereby a distant attacker can generate a malformed potential attack whereby a distant attacker can generate a malformed
optional transitive attribute that is not recognized by intervening optional transitive attribute that is not recognized by intervening
routers. Since the intervening routers do not recognize the routers. Since the intervening routers do not recognize the
attribute, they propagate it without checking it. When the malformed attribute, they propagate it without checking it. When the malformed
attribute arrives at a router that does recognize the given attribute attribute arrives at a router that does recognize the given attribute
type, that router resets the session over which it arrived. Since type, that router resets the session over which it arrived. Since
significant fan-out can occur between the attacker and the routers significant fan-out can occur between the attacker and the routers
that do recognize the attribute type, this attack could potentially that do recognize the attribute type, this attack could potentially
be particularly harmful. be particularly harmful.
The improved error handling of this specification could in theory The improved error handling of this specification could in theory
interact badly with some now-known weaker cryptographic mechanisms interact badly with some now-known weaker cryptographic mechanisms
should such be used in future to secure BGP. For example, if a should such be used in future to secure BGP. For example, if a
(fictional) mechanism that did not supply data integrity was used, an (fictional) mechanism that did not supply data integrity was used, an
attacker could manipulate ciphertext in any attempt to change or attacker could manipulate ciphertext in any attempt to change or
observe how the receiver reacts. Absent this specification, the BGP observe how the receiver reacts. Absent this specification, the BGP
session would have been terminated, while with this specification the session would have been terminated; with this specification, the
attacker could make potentially many attempts. While such a attacker could make potentially many attempts. While such a
confidentiality-only mechanism would not be defined today, we have in confidentiality-only mechanism would not be defined today, we have in
the past seen mechanism definitions that result in similar though not the past seen mechanism definitions that result in similar, though
as obviously exploitable vulnerabilities. [RFC7366] The approach not as obviously exploitable, vulnerabilities [RFC7366]. The
recommended today to avoid such issues is to prefer use of approach recommended today to avoid such issues is to prefer use of
Authenticated Encryption with Additional Data (AEAD) ciphers Authenticated Encryption with Additional Data (AEAD) ciphers
[RFC5116] and (thus) to discard messages that don't verify. [RFC5116] and thus to discard messages that don't verify.
In other respects, this specification does not change BGP's security In other respects, this specification does not change BGP's security
characteristics. characteristics.
11. Acknowledgements 10. References
The authors wish to thank Juan Alcaide, Deniz Bahadir, Ron Bonica,
Mach Chen, Andy Davidson, Bruno Decraene, Stephen Farrell, Rex
Fernando, Jeff Haas, Chris Hall, Joel Halpern, Dong Jie, Akira Kato,
Miya Kohno, Warren Kumari, 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 10.1. Normative References
[IANA-BGP-ATTRS] [IANA-BGP-ATTRS]
"BGP Path Attributes", <http://www.iana.org/assignments/ IANA, "BGP Path Attributes",
bgp-parameters/bgp-parameters.xhtml#bgp-parameters-2>. <http://www.iana.org/assignments/bgp-parameters>.
[RFC1997] Chandrasekeran, R., Traina, P., and T. Li, "BGP [RFC1997] Chandra, R., Traina, P., and T. Li, "BGP Communities
Communities Attribute", RFC 1997, August 1996. Attribute", RFC 1997, DOI 10.17487/RFC1997, August 1996,
<http://www.rfc-editor.org/info/rfc1997>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Protocol 4 (BGP-4)", RFC 4271, January 2006. Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<http://www.rfc-editor.org/info/rfc4271>.
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended [RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, February 2006. Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
February 2006, <http://www.rfc-editor.org/info/rfc4360>.
[RFC4456] Bates, T., Chen, E., and R. Chandra, "BGP Route [RFC4456] Bates, T., Chen, E., and R. Chandra, "BGP Route
Reflection: An Alternative to Full Mesh Internal BGP Reflection: An Alternative to Full Mesh Internal BGP
(IBGP)", RFC 4456, April 2006. (IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006,
<http://www.rfc-editor.org/info/rfc4456>.
[RFC4724] Sangli, S., Chen, E., Fernando, R., Scudder, J., and Y. [RFC4724] Sangli, S., Chen, E., Fernando, R., Scudder, J., and Y.
Rekhter, "Graceful Restart Mechanism for BGP", RFC 4724, Rekhter, "Graceful Restart Mechanism for BGP", RFC 4724,
January 2007. DOI 10.17487/RFC4724, January 2007,
<http://www.rfc-editor.org/info/rfc4724>.
[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, [RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760, January "Multiprotocol Extensions for BGP-4", RFC 4760,
2007. DOI 10.17487/RFC4760, January 2007,
<http://www.rfc-editor.org/info/rfc4760>.
[RFC5543] Ould-Brahim, H., Fedyk, D., and Y. Rekhter, "BGP Traffic [RFC5543] Ould-Brahim, H., Fedyk, D., and Y. Rekhter, "BGP Traffic
Engineering Attribute", RFC 5543, May 2009. Engineering Attribute", RFC 5543, DOI 10.17487/RFC5543,
May 2009, <http://www.rfc-editor.org/info/rfc5543>.
[RFC5701] Rekhter, Y., "IPv6 Address Specific BGP Extended Community [RFC5701] Rekhter, Y., "IPv6 Address Specific BGP Extended Community
Attribute", RFC 5701, November 2009. Attribute", RFC 5701, DOI 10.17487/RFC5701, November 2009,
<http://www.rfc-editor.org/info/rfc5701>.
[RFC6368] Marques, P., Raszuk, R., Patel, K., Kumaki, K., and T. [RFC6368] Marques, P., Raszuk, R., Patel, K., Kumaki, K., and T.
Yamagata, "Internal BGP as the Provider/Customer Edge Yamagata, "Internal BGP as the Provider/Customer Edge
Protocol for BGP/MPLS IP Virtual Private Networks (VPNs)", Protocol for BGP/MPLS IP Virtual Private Networks (VPNs)",
RFC 6368, September 2011. RFC 6368, DOI 10.17487/RFC6368, September 2011,
<http://www.rfc-editor.org/info/rfc6368>.
[RFC6793] Vohra, Q. and E. Chen, "BGP Support for Four-Octet [RFC6793] Vohra, Q. and E. Chen, "BGP Support for Four-Octet
Autonomous System (AS) Number Space", RFC 6793, December Autonomous System (AS) Number Space", RFC 6793,
2012. DOI 10.17487/RFC6793, December 2012,
<http://www.rfc-editor.org/info/rfc6793>.
12.2. Informative References 10.2. Informative References
[RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated [RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated
Encryption", RFC 5116, January 2008. Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,
<http://www.rfc-editor.org/info/rfc5116>.
[RFC5549] Le Faucheur, F. and E. Rosen, "Advertising IPv4 Network [RFC5549] Le Faucheur, F. and E. Rosen, "Advertising IPv4 Network
Layer Reachability Information with an IPv6 Next Hop", RFC Layer Reachability Information with an IPv6 Next Hop",
5549, May 2009. RFC 5549, DOI 10.17487/RFC5549, May 2009,
<http://www.rfc-editor.org/info/rfc5549>.
[RFC6514] Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP [RFC6514] Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
Encodings and Procedures for Multicast in MPLS/BGP IP Encodings and Procedures for Multicast in MPLS/BGP IP
VPNs", RFC 6514, February 2012. VPNs", RFC 6514, DOI 10.17487/RFC6514, February 2012,
<http://www.rfc-editor.org/info/rfc6514>.
[RFC7117] Aggarwal, R., Kamite, Y., Fang, L., Rekhter, Y., and C. [RFC7117] Aggarwal, R., Ed., Kamite, Y., Fang, L., Rekhter, Y., and
Kodeboniya, "Multicast in Virtual Private LAN Service C. Kodeboniya, "Multicast in Virtual Private LAN Service
(VPLS)", RFC 7117, February 2014. (VPLS)", RFC 7117, DOI 10.17487/RFC7117, February 2014,
<http://www.rfc-editor.org/info/rfc7117>.
[RFC7366] Gutmann, P., "Encrypt-then-MAC for Transport Layer [RFC7366] Gutmann, P., "Encrypt-then-MAC for Transport Layer
Security (TLS) and Datagram Transport Layer Security Security (TLS) and Datagram Transport Layer Security
(DTLS)", RFC 7366, September 2014. (DTLS)", RFC 7366, DOI 10.17487/RFC7366, September 2014,
<http://www.rfc-editor.org/info/rfc7366>.
[RFC7432] Sajassi, A., Aggarwal, R., Bitar, N., Isaac, A., Uttaro, [RFC7432] Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
J., Drake, J., and W. Henderickx, "BGP MPLS-Based Ethernet Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
VPN", RFC 7432, February 2015. Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February
2015, <http://www.rfc-editor.org/info/rfc7432>.
Acknowledgements
The authors wish to thank Juan Alcaide, Deniz Bahadir, Ron Bonica,
Mach Chen, Andy Davidson, Bruno Decraene, Stephen Farrell, Rex
Fernando, Jeff Haas, Chris Hall, Joel Halpern, Dong Jie, Akira Kato,
Miya Kohno, Warren Kumari, 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.
Authors' Addresses Authors' Addresses
Enke Chen (editor) Enke Chen (editor)
Cisco Systems, Inc. Cisco Systems, Inc.
Email: enkechen@cisco.com Email: enkechen@cisco.com
John G. Scudder (editor) John G. Scudder (editor)
Juniper Networks Juniper Networks
Email: jgs@juniper.net Email: jgs@juniper.net
Pradosh Mohapatra Pradosh Mohapatra
Sproute Networks Sproute Networks
Email: mpradosh@yahoo.com Email: mpradosh@yahoo.com
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