draft-ietf-idr-error-handling-07.txt   draft-ietf-idr-error-handling-08.txt 
Internet Engineering Task Force E. Chen, Ed. Internet Engineering Task Force E. Chen, Ed.
Internet-Draft Cisco Systems, Inc. Internet-Draft Cisco Systems, Inc.
Updates: 1997, 4271, 4360, 4456, 4760, 5701 (if approved)J. Scudder, Ed. Updates: 1997, 4271, 4360, 4456, 4760, 5701(if approved) J. Scudder, Ed.
Intended status: Standards Track Juniper Networks Intended status: Standards Track Juniper Networks
Expires: November 8, 2014 P. Mohapatra Expires: November 15, 2014 P. Mohapatra
Sproute Networks Sproute Networks
K. Patel K. Patel
Cisco Systems, Inc. Cisco Systems, Inc.
May 7, 2014 May 14, 2014
Revised Error Handling for BGP UPDATE Messages Revised Error Handling for BGP UPDATE Messages
draft-ietf-idr-error-handling-07 draft-ietf-idr-error-handling-08
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 as a session reset would impact not only This behavior is undesirable as a session reset would impact not only
routes with the offending attribute, but also other valid routes routes with the offending attribute, but also other valid routes
exchanged over the session. This document partially revises the exchanged over the session. This document partially revises the
error handling for UPDATE messages, and provides guidelines for the error handling for UPDATE messages, and provides guidelines for the
authors of documents defining new attributes. Finally, it revises authors of documents defining new attributes. Finally, it revises
the error handling procedures for a number of existing attributes. the error handling procedures for a number of existing attributes.
This document updates error handling for RFCs 1997, 4271, 4360, 4456, This document updates error handling for RFCs 1997, 4271, 4360, 4456,
4760, and 5701. 4760 and 5701.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
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Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." 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 Notice
Copyright (c) 2014 IETF Trust and the persons identified as the Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Without obtaining an adequate license from the person(s) controlling Without obtaining an adequate license from the person(s) controlling
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outside the IETF Standards Process, and derivative works of it may outside the IETF Standards Process, and derivative works of it may
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than English. than English.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Revision to Base Specification . . . . . . . . . . . . . . . 4 2. Error-Handling Approaches . . . . . . . . . . . . . . . . . . 4
3. Parsing of NLRI Fields . . . . . . . . . . . . . . . . . . . 6 3. Revision to BGP UPDATE Message Error Handling . . . . . . . . 4
3.1. Inconsistency of Attribute Length Fields . . . . . . . . 6 4. Parsing of NLRI Fields . . . . . . . . . . . . . . . . . . . 6
3.2. Syntactic Correctness of NLRI Fields . . . . . . . . . . 7 4.1. Attribute Length Fields . . . . . . . . . . . . . . . . . 7
3.3. Typed NLRI . . . . . . . . . . . . . . . . . . . . . . . 7 4.2. Syntactic Correctness of NLRI Fields . . . . . . . . . . 7
4. Operational Considerations . . . . . . . . . . . . . . . . . 8 4.3. Typed NLRI . . . . . . . . . . . . . . . . . . . . . . . 8
5. Error Handling Procedures for Existing Attributes . . . . . . 9 5. Operational Considerations . . . . . . . . . . . . . . . . . 8
5.1. ORIGIN . . . . . . . . . . . . . . . . . . . . . . . . . 9 6. Error Handling Procedures for Existing Attributes . . . . . . 9
5.2. AS_PATH . . . . . . . . . . . . . . . . . . . . . . . . . 9 6.1. ORIGIN . . . . . . . . . . . . . . . . . . . . . . . . . 9
5.3. NEXT_HOP . . . . . . . . . . . . . . . . . . . . . . . . 9 6.2. AS_PATH . . . . . . . . . . . . . . . . . . . . . . . . . 9
5.4. MULTI_EXIT_DESC . . . . . . . . . . . . . . . . . . . . . 9 6.3. NEXT_HOP . . . . . . . . . . . . . . . . . . . . . . . . 10
5.5. LOCAL_PREF . . . . . . . . . . . . . . . . . . . . . . . 9 6.4. MULTI_EXIT_DISC . . . . . . . . . . . . . . . . . . . . . 10
5.6. ATOMIC_AGGREGATE . . . . . . . . . . . . . . . . . . . . 10 6.5. LOCAL_PREF . . . . . . . . . . . . . . . . . . . . . . . 10
5.7. AGGREGATOR . . . . . . . . . . . . . . . . . . . . . . . 10 6.6. ATOMIC_AGGREGATE . . . . . . . . . . . . . . . . . . . . 10
5.8. Community . . . . . . . . . . . . . . . . . . . . . . . . 10 6.7. AGGREGATOR . . . . . . . . . . . . . . . . . . . . . . . 11
5.9. Extended Community . . . . . . . . . . . . . . . . . . . 10 6.8. Community . . . . . . . . . . . . . . . . . . . . . . . . 11
5.10. IPv6 Address Specific BGP Extended Community Attribute . 11 6.9. Extended Community . . . . . . . . . . . . . . . . . . . 11
5.11. ORIGINATOR_ID . . . . . . . . . . . . . . . . . . . . . . 11 6.10. IPv6 Address Specific BGP Extended Community Attribute . 11
5.12. CLUSTER_LIST . . . . . . . . . . . . . . . . . . . . . . 11 6.11. ORIGINATOR_ID . . . . . . . . . . . . . . . . . . . . . . 12
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 6.12. CLUSTER_LIST . . . . . . . . . . . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12 6.13. MP_REACH_NLRI and MP_UNREACH_NLRI . . . . . . . . . . . . 12
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 7. Guidance for Authors of BGP Specifications . . . . . . . . . 12
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
9.1. Normative References . . . . . . . . . . . . . . . . . . 12 9. Security Considerations . . . . . . . . . . . . . . . . . . . 13
9.2. Informative References . . . . . . . . . . . . . . . . . 13 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
11.1. Normative References . . . . . . . . . . . . . . . . . . 13
11.2. Informative References . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
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 as a session reset would received. This behavior is undesirable as a session reset would
impact not only routes with the offending attribute, but also other impact 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. The reason is that such present a potential security vulnerability. The reason is that such
attributes may have been propagated without being checked by attributes may have been propagated without being checked by
intermediate routers that do not recognize the attributes -- in intermediate routers that do not recognize the attributes -- in
effect the attribute may have been tunneled, and when they do reach a 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 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 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 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] and [RFC5701] are revised. [RFC4456], [RFC4760] and [RFC5701] are 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. Revision to Base Specification 2. Error-Handling Approaches
The first paragraph of Section 6.3 of [RFC4271] is revised as In this document we refer to three different approaches to handling
follows: 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):
Old Text: o Session reset: This is the approach used throughout the base BGP
specification [RFC4271], where a NOTIFICATION is sent and the
session terminated.
All errors detected while processing the UPDATE message MUST be o Treat-as-withdraw: In this approach, the UPDATE message containing
indicated by sending the NOTIFICATION message with the Error Code the path attribute in question MUST be treated as though all
UPDATE Message Error. The error subcode elaborates on the contained routes had been withdrawn just as if they had been
specific nature of the error. 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].
New text: 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.
An error detected while processing the UPDATE message for which a 3. Revision to BGP UPDATE Message Error Handling
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 This specification amends [RFC4271] Section 6.3 in a number of ways.
[RFC4271] remains unchanged: See also Section 6 for treatment of specific path attributes.
If the Withdrawn Routes Length or Total Attribute Length is too a. The first paragraph is revised as follows:
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 Old Text:
[RFC4271] is revised
If any recognized attribute has Attribute Flags that conflict with All errors detected while processing the UPDATE message
the Attribute Type Code, then the Error Subcode MUST be set to MUST be indicated by sending the NOTIFICATION message with
Attribute Flags Error. The Data field MUST contain the erroneous the Error Code UPDATE Message Error. The error subcode
attribute (type, length, and value). elaborates on the specific nature of the error.
as follows: New text:
If any recognized attribute has Attribute Flags that conflict with An error detected while processing the UPDATE message for
the Attribute Type Code, then the attribute MUST be treated as which a session reset is specified MUST be indicated by
malformed and the treat-as-withdraw approach (see below) used, sending the NOTIFICATION message with the Error Code UPDATE
unless the specification for the attribute mandates different Message Error. The error subcode elaborates on the
handling for incorrect Attribute Flags. specific nature of the error.
The error handling of all other cases involving path attributes as b. Error handling for the following case remains unchanged:
described in Section 6.3 of [RFC4271] that specify a session reset is
revised as follows.
When a path attribute (other than the MP_REACH_NLRI attribute If the Withdrawn Routes Length or Total Attribute Length is
[RFC4760] or the MP_UNREACH_NLRI attribute [RFC4760]) in an UPDATE too large (i.e., if Withdrawn Routes Length + Total
message is determined to be malformed, the UPDATE message containing Attribute Length + 23 exceeds the message Length), then the
that attribute MUST be treated as though all contained routes had Error Subcode MUST be set to Malformed Attribute List.
been withdrawn just as if they had been listed in the WITHDRAWN
ROUTES field (or in the MP_UNREACH_NLRI attribute if appropriate) of
the UPDATE message, thus causing them to be removed from the Adj-RIB-
In according to the procedures of [RFC4271]. In the case of an
attribute which has no effect on route selection or installation, the
malformed attribute MAY instead be discarded and the UPDATE message
continue to be processed. For the sake of brevity, the former
approach is termed "treat-as-withdraw", and the latter as "attribute
discard".
If any of the well-known mandatory attributes are not present in an c. Attribute Flag error handling is revised as follows:
UPDATE message, then the approach of "treat-as-withdraw" MUST be used
for the error handling.
The approach of "treat-as-withdraw" MUST be used for the error Old Text:
handling of the cases described in Section 6.3 of [RFC4271] that
specify a session reset and involve any of the following attributes:
ORIGIN, AS_PATH, NEXT_HOP, MULTI_EXIT_DISC, and LOCAL_PREF.
The approach of "attribute discard" MUST be used for the error If any recognized attribute has Attribute Flags that
handling of the cases described in Section 6.3 of [RFC4271] that conflict with the Attribute Type Code, then the Error
specify a session reset and involve any of the following attributes: Subcode MUST be set to Attribute Flags Error. The Data
ATOMIC_AGGREGATE and AGGREGATOR. field MUST contain the erroneous attribute (type, length,
and value).
If the MP_REACH_NLRI attribute or the MP_UNREACH_NLRI attribute New Text:
appears more than once in the UPDATE message, then a NOTIFICATION
message MUST be sent with the Error Subcode "Malformed Attribute
List". If any other attribute appears more than once in an UPDATE
message, then all the occurrences of the attribute other than the
first one SHALL be discarded and the UPDATE message continue to be
processed.
When multiple attribute errors exist in an UPDATE message, if the If any recognized attribute has Attribute Flags that
same approach (either "session reset", or "treat-as-withdraw" or conflict with the Attribute Type Code, then the attribute
"attribute discard") is specified for the handling of these malformed MUST be treated as malformed and the treat-as-withdraw
attributes, then the specified approach MUST be used. Otherwise the approach used, unless the specification for the attribute
approach with the strongest action MUST be used following the order mandates different handling for incorrect Attribute Flags.
of "session reset", "treat-as-withdraw" and "attribute discard" from
the strongest to the weakest.
A document which specifies a new attribute MUST provide specifics d. If any of the well-known mandatory attributes are not present in
regarding what constitutes an error for that attribute and how that an UPDATE message, then "treat-as-withdraw" MUST be used.
error is to be handled.
Finally, we observe that in order to use the approach of "treat-as- e. "Treat-as-withdraw" MUST be used for the cases that specify a
withdraw", the entire NLRI field and/or the MP_REACH_NLRI and session reset and involve any of the attributes ORIGIN, AS_PATH,
MP_UNREACH_NLRI attributes need to be successfully parsed. If this NEXT_HOP, MULTI_EXIT_DISC, or LOCAL_PREF.
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:
The NLRI field in the UPDATE message is checked for syntactic f. "Attribute discard" MUST be used for any of the cases that
validity. If the field is syntactically incorrect, then the Error specify a session reset and involve ATOMIC_AGGREGATE or
Subcode MUST be set to Invalid Network Field. AGGREGATOR.
Furthermore, this document extends RFC 4271 by mandating that the g. If the MP_REACH_NLRI attribute or the MP_UNREACH_NLRI [RFC4760]
Withdrawn Routes field SHALL be checked for syntactic correctness in attribute appears more than once in the UPDATE message, then a
the same manner as the NLRI field. 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.
3. Parsing of NLRI Fields 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.
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.
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.
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.
4. Parsing of NLRI Fields
To facilitate the determination of the NLRI field in an UPDATE with a To facilitate the determination of the NLRI field in an UPDATE with a
malformed attribute, the MP_REACH_NLRI or MP_UNREACH_NLRI attribute malformed attribute, the following restrictions on encoding NLRI MUST
(if present) SHALL be encoded as the very first path attribute in an be followed:
UPDATE. An implementation, however, MUST still be prepared to
receive these fields in any position. 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 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. When such an UPDATE is received, we observe
that the NLRI field can be determined using the "Message Length", that the NLRI field can be determined using the "Message Length",
"Withdrawn Route Length" and "Total Attribute Length" (when they are "Withdrawn Route Length" and "Total Attribute Length" (when they are
consistent) carried in the message instead of relying on the length consistent) carried in the message instead of relying on the length
of individual attributes in the message. 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 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. In the "overrun" case, as the
enclosed path attributes are parsed, the length of the last enclosed path attributes are parsed, the length of the last
encountered path attribute would cause the Total Attribute Length to encountered path attribute would cause the Total Attribute Length to
be exceeded. In the "underrun" case, as the enclosed path attributes be exceeded. In the "underrun" case, as the enclosed path attributes
are parsed, after the last successfully-parsed attribute, fewer than are parsed, after the last successfully-parsed attribute, fewer than
three bytes remain, or fewer than four bytes, if the Attribute Flags three octets remain, or fewer than four octets, if the Attribute
field has the Extended Length bit set -- that is, there remains Flags field has the Extended Length bit set -- that is, there remains
unconsumed data in the path attributes but yet insufficient data to unconsumed data in the path attributes but yet insufficient data to
encode a single minimum-sized path attribute. In either of these encode a single minimum-sized path attribute. In either of these
cases an error condition exists and the treat-as-withdraw approach cases an error condition exists and the treat-as-withdraw approach
MUST be used (unless some other, more severe error is encountered MUST be used (unless some other, more severe error is encountered
dictating a stronger approach), and the Total Attribute Length MUST dictating a stronger approach), and the Total Attribute Length MUST
be relied upon to enable the beginning of the NLRI field to be be relied upon to enable the beginning of the NLRI field to be
located. 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 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.
skipping to change at page 7, line 39 skipping to change at page 8, line 19
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 attribute is less than 3, or the o The length of the MP_UNREACH attribute is less than 3, or the
length of the MP_REACH attribute is less than 5. 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 Certain address families, for example MVPN [RFC7117] and EVPN
[I-D.ietf-l2vpn-evpn] have NLRI that are typed. Since supported type [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 capability [RFC4760], it is possible for a BGP speaker to advertise
support for the given address family and sub-address family while support for the given address family and sub-address family while
still not supporting a particular type of NLRI within that AFI/SAFI. still not supporting a particular type of 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.
4. Operational Considerations 5. 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 received on an IBGP session is subjected to this
treatment, inconsistent routing within the affected Autonomous System treatment, inconsistent routing within the affected Autonomous System
may result. The consequences of inconsistent routing can include may result. The consequences of inconsistent routing can include
long-lived forwarding loops and black holes. While lamentable, this long-lived forwarding loops and black holes. While lamentable, this
issue is expected to be rare in practice, and more importantly is issue is expected to be rare in practice, and more importantly is
seen as less problematic than the session-reset behavior it replaces. seen as less problematic than the session-reset behavior it replaces.
skipping to change at page 8, line 33 skipping to change at page 9, line 14
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 sub-optimal
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 incremental
update, and could cause invalid routes to be kept. 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 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.
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 The attribute is considered malformed if its length is not 1, or 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".
5.2. AS_PATH 6.2. AS_PATH
The error conditions for the attribute have been defined in An AS_PATH is considered malformed if an unrecognized segment type is
[RFC4271]. 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 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".
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 6.3. NEXT_HOP
[RFC4271].
The attribute is considered malformed if it is syntactically
incorrect according to [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".
5.4. MULTI_EXIT_DESC 6.4. 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_DESC attribute SHALL be An UPDATE message with a malformed MULTI_EXIT_DESC attribute SHALL be
handled using the approach of "treat-as-withdraw". handled using the approach of "treat-as-withdraw".
5.5. LOCAL_PREF 6.5. LOCAL_PREF
The attribute is considered malformed if its length is not 4
[RFC4271].
An UPDATE message with a malformed LOCAL_PREF attribute SHALL be
handled as follows:
o using the approach of "attribute discard" if the UPDATE message is The error handling of [RFC4271] is revised as follows.
received from an external neighbor, or
o using the approach of "treat-as-withdraw" if the UPDATE message is o If the LOCAL_PREF attribute is received from an external neighbor,
received from an internal 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 o if received from an internal neighbor, it SHALL be considered
external neighbor, the approach of "attribute discard" SHALL be used malformed if its length is not equal to 4. If malformed, the
to handle the unexpected attribute in the message. 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 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".
5.7. AGGREGATOR 6.7. 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 advertised to, or not received from the peer [RFC6793]). not 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 advertised to, and received from the peer). both 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".
5.8. Community 6.8. 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 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 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".
5.9. Extended Community 6.9. 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 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 An UPDATE message with a malformed Extended Community attribute SHALL
be handled using the approach of "treat-as-withdraw". 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.
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 error handling of [RFC5701] is revised as follows:
The IPv6 Address Specific Extended Community attribute SHALL be The IPv6 Address Specific Extended Community attribute SHALL be
considered malformed if its length is nonzero and is not a multiple considered malformed if its length is not a nonzero multiple of 20.
of 20.
An UPDATE message with a malformed IPv6 Address Specific Extended 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-as-
withdraw". 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.
5.11. ORIGINATOR_ID 6.11. 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 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. 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 multiple 4. If malformed, the malformed if its length is not a nonzero multiple of 4. If
UPDATE SHALL be handled using the approach of "treat-as-withdraw". 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. This document makes no request of IANA.
7. Security Considerations 9. 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 (which thus propagate the attribute unchecked) but that routers (which thus propagate the attribute unchecked) but that
causes session resets when it reaches routers that do recognize the causes session resets when it reaches routers that do recognize the
given attribute type. given attribute type.
In other respects, this specification does not change BGP's security In other respects, this specification does not change BGP's security
characteristics. characteristics.
8. Acknowledgements 10. Acknowledgements
The authors wish to thank Juan Alcaide, Ron Bonica, Mach Chen, Andy The authors wish to thank Juan Alcaide, Ron Bonica, Mach Chen, Andy
Davidson, Bruno Decraene, Rex Fernando, Jeff Haas, Joel Halpern, Dong Davidson, Bruno Decraene, Rex Fernando, Jeff Haas, Chris Hall, Joel
Jie, Akira Kato, Miya Kohno, Tony Li, Alton Lo, Shin Miyakawa, Tamas Halpern, Dong Jie, Akira Kato, Miya Kohno, Tony Li, Alton Lo, Shin
Mondal, Jonathan Oddy, Tony Przygienda, Robert Raszuk, Yakov Rekhter, Miyakawa, Tamas Mondal, Jonathan Oddy, Tony Przygienda, Robert
Eric Rosen, Shyam Sethuram, Rob Shakir, Naiming Shen, Adam Simpson, Raszuk, Yakov Rekhter, Eric Rosen, Shyam Sethuram, Rob Shakir,
Ananth Suryanarayana, Kaliraj Vairavakkalai and Lili Wang for their Naiming Shen, Adam Simpson, Ananth Suryanarayana, Kaliraj
observations and discussion of this topic, and review of this Vairavakkalai, Lili Wang and Ondrej Zajicek for their observations
document. 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 [RFC1997] Chandrasekeran, R., Traina, P., and T. Li, "BGP
Communities Attribute", RFC 1997, August 1996. Communities Attribute", RFC 1997, August 1996.
[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, March 1997.
[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway [RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, January 2006. Protocol 4 (BGP-4)", RFC 4271, January 2006.
skipping to change at page 13, line 12 skipping to change at page 14, line 23
"Multiprotocol Extensions for BGP-4", RFC 4760, January "Multiprotocol Extensions for BGP-4", RFC 4760, January
2007. 2007.
[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, November 2009.
[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, December
2012. 2012.
9.2. Informative References 11.2. Informative References
[I-D.ietf-l2vpn-evpn] [I-D.ietf-l2vpn-evpn]
Sajassi, A., Aggarwal, R., Bitar, N., Isaac, A., and J. Sajassi, A., Aggarwal, R., Bitar, N., Isaac, A., and J.
Uttaro, "BGP MPLS Based Ethernet VPN", draft-ietf-l2vpn- 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. [RFC7117] Aggarwal, R., Kamite, Y., Fang, L., Rekhter, Y., and C.
Kodeboniya, "Multicast in Virtual Private LAN Service Kodeboniya, "Multicast in Virtual Private LAN Service
(VPLS)", RFC 7117, February 2014. (VPLS)", RFC 7117, February 2014.
Authors' Addresses Authors' Addresses
Enke Chen (editor) Enke Chen (editor)
Cisco Systems, Inc. Cisco Systems, Inc.
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