Enhanced Route Refresh Capability for BGP-4
Begin and end markers that let BGP routers check and repair each other's routing tables without disruption.
Patel, K., Chen, E., and B. Venkatachalapathy, "Enhanced Route Refresh Capability for BGP-4", RFC 7313, DOI 10.17487/RFC7313, July 2014, <https://www.rfc-editor.org/info/rfc7313>.
@misc{rfc7313,
series = {Request for Comments},
number = 7313,
howpublished = {RFC 7313},
publisher = {RFC Editor},
doi = {10.17487/RFC7313},
url = {https://www.rfc-editor.org/info/rfc7313},
author = {K. Patel and E. Chen and B. Venkatachalapathy},
title = {{Enhanced Route Refresh Capability for BGP-4}},
pagetotal = 8,
year = 2014,
month = jul,
} RFC text
Contents
Internet Engineering Task Force (IETF) K. Patel
Request for Comments: 7313 E. Chen
Updates: 2918 Cisco Systems
Category: Standards Track B. Venkatachalapathy
ISSN: 2070-1721 July 2014
Enhanced Route Refresh Capability for BGP-4
Abstract
In this document, we enhance the existing BGP route refresh
mechanisms to provide for the demarcation of the beginning and the
ending of a route refresh. The enhancement can be used to facilitate
correction of BGP Routing Information Base (RIB) inconsistencies in a
non-disruptive manner. This document updates RFC 2918.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
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/rfc7313.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 2
3. Protocol Extensions . . . . . . . . . . . . . . . . . . . . . 2
3.1. Enhanced Route Refresh Capability . . . . . . . . . . . . 3
3.2. Subtypes for ROUTE-REFRESH Message . . . . . . . . . . . 3
4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 3
5. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
9. Normative References . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
It is sometimes necessary to perform routing consistency validations
such as checking for possible missing route withdrawals between BGP
speakers [RFC4271]. Currently, such validations typically involve
offline, manual operations that can be tedious and time-consuming.
In this document, we enhance the existing BGP route refresh
mechanisms [RFC2918] to provide for the demarcation of the beginning
and the ending of a route refresh (which refers to the complete
re-advertisement of the Adj-RIB-Out to a peer, subject to routing
policies). The enhancement can be used to facilitate online, non-
disruptive consistency validation of BGP routing updates.
This document updates [RFC2918] by redefining a field in the ROUTE-
REFRESH message that was previously designated as Reserved.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119] only when
they appear in all upper case. They may also appear in lower or
mixed case as English words, without any normative meaning.
3. Protocol Extensions
The BGP protocol extensions introduced in this document include the
definition of a new BGP capability, named "Enhanced Route Refresh
Capability", and the specification of the message subtypes for the
ROUTE-REFRESH message.
3.1. Enhanced Route Refresh Capability
The "Enhanced Route Refresh Capability" is a new BGP capability
[RFC5492]. IANA has assigned a Capability Code of 70 for this
capability. The Capability Length field of this capability is zero.
By advertising this capability to a peer, a BGP speaker conveys to
the peer that the speaker supports the message subtypes for the
ROUTE-REFRESH message and the related procedures described in this
document.
3.2. Subtypes for ROUTE-REFRESH Message
The "Reserved" field of the ROUTE-REFRESH message specified in
[RFC2918] is redefined as the "Message Subtype" with the following
values:
0 - Normal route refresh request [RFC2918]
with/without Outbound Route Filtering (ORF) [RFC5291]
1 - Demarcation of the beginning of a route refresh
(BoRR) operation
2 - Demarcation of the ending of a route refresh
(EoRR) operation
255 - Reserved
The remaining values of the message subtypes are reserved for future
use; see Section 6 ("IANA Considerations"). The use of the new
message subtypes is described in Section 4 ("Operation").
4. Operation
A BGP speaker that supports the message subtypes for the ROUTE-
REFRESH message and the related procedures SHOULD advertise the
"Enhanced Route Refresh Capability".
The following procedures are applicable only if a BGP speaker has
received the "Enhanced Route Refresh Capability" from a peer.
Before the speaker starts a route refresh that is either initiated
locally, or in response to a "normal route refresh request" from the
peer, the speaker MUST send a BoRR message. After the speaker
completes the re-advertisement of the entire Adj-RIB-Out to the peer,
it MUST send an EoRR message.
Conceptually, the "entire Adj-RIB-Out" for a peer in this section
refers to all the route entries in the "Adj-RIB-Out" for the peer at
the start of the route refresh operation. These route entries
comprise both the reachability as well as unreachability information.
When a route entry in the "Adj-RIB-Out" changes, only the modified
route entry needs to be advertised.
In processing a ROUTE-REFRESH message from a peer, the BGP speaker
MUST examine the "message subtype" field of the message and take the
appropriate actions. The message processing rules for ROUTE-REFRESH
message with subtype of 0 are described in [RFC2918] and [RFC5291].
A BGP speaker can receive a BoRR message from a peer at any time,
either as a result of a peer responding to a ROUTE-REFRESH message,
or as a result of a peer unilaterally initiating a route refresh.
When a BGP speaker receives a BoRR message from a peer, it MUST mark
all the routes with the given Address Family Identifier and
Subsequent Address Family Identifier, <AFI, SAFI> [RFC2918], from
that peer as stale. As it receives routes from its peer's subsequent
Adj-RIB-Out re-advertisement, these replace any corresponding stale
routes. When a BGP speaker receives an EoRR message from a peer, it
MUST immediately remove any routes from the peer that are still
marked as stale for that <AFI, SAFI>. Such purged routes MAY be
logged for future analysis. A BGP speaker MAY ignore any EoRR
message received without a prior receipt of an associated BoRR
message. Such messages MAY be logged for future analysis.
An implementation MAY impose a locally configurable upper bound on
how long it would retain any stale routes. Once the upper bound is
reached, the implementation MAY remove any routes from the peer that
are still marked as stale for that <AFI, SAFI> without waiting for an
EoRR message.
The following procedures are specified in order to simplify the
interaction with the BGP Graceful Restart [RFC4724]. In particular,
these procedures ensure that End-of-RIB (EoR) defined in Graceful
Restart and EoRR as defined in this specification are kept separate,
thereby avoiding any premature cleanup of stale routes. For a BGP
speaker that supports the BGP Graceful Restart, it MUST NOT send a
BoRR for an <AFI, SAFI> to a neighbor before it sends the EoR for the
<AFI, SAFI> to the neighbor. A BGP speaker that has received the
Graceful Restart Capability from its neighbor MUST ignore any BoRRs
for an <AFI, SAFI> from the neighbor before the speaker receives the
EoR for the given <AFI, SAFI> from the neighbor. The BGP speaker
SHOULD log an error of the condition for further analysis.
5. Error Handling
This document defines a new NOTIFICATION error code:
Error Code Name
7 ROUTE-REFRESH Message Error
The following error subcode is defined as well:
Subcode Name
1 Invalid Message Length
The error handling specified in this section is applicable only when
a BGP speaker has received the "Enhanced Route Refresh Capability"
from a peer.
If the length, excluding the fixed-size message header, of the
received ROUTE-REFRESH message with Message Subtype 1 and 2 is not 4,
then the BGP speaker MUST send a NOTIFICATION message with the Error
Code of "ROUTE-REFRESH Message Error" and the subcode of "Invalid
Message Length". The Data field of the NOTIFICATION message MUST
contain the complete ROUTE-REFRESH message.
When the BGP speaker receives a ROUTE-REFRESH message with a "Message
Subtype" field other than 0, 1, or 2, it MUST ignore the received
ROUTE-REFRESH message. It SHOULD log an error for further analysis.
6. IANA Considerations
This document defines the Enhanced Route Refresh Capability for BGP.
In the "Capability Codes" registry, IANA has assigned it value 70,
referencing this document.
This document also defines two new subcodes for the Route Refresh
message. They have been registered with the IANA in a new registry
as follows:
Under "Border Gateway Protocol (BGP) Parameters":
Registry: "BGP Route Refresh Subcodes"
Reference: [RFC7313]
Registration Procedure(s): Values 0-127 Standards Action,
values 128-254 First Come First Served
Value Code Reference
0 Route-Refresh [RFC2918], [RFC5291]
1 BoRR [RFC7313]
2 EoRR [RFC7313]
3-254 Unassigned
255 Reserved [RFC7313]
In addition, this document defines a NOTIFICATION error code and an
error subcode related to the ROUTE-REFRESH message. IANA has changed
the name of the "BGP Error Codes" to "BGP Error (Notification) Codes"
and added this document as a reference. IANA has allocated a new
error code from that registry with the name "ROUTE-REFRESH Message
Error", referencing this document.
IANA has created a new registry for the error subcodes as follows:
Under "Border Gateway Protocol (BGP) Parameters",
under "BGP Error Subcodes":
Registry: "BGP ROUTE-REFRESH Message Error subcodes"
Reference: [RFC7313]
Registration Procedure(s): Values 0-127 Standards Action,
values 128-255 First Come First Served
Value Name Reference
0 Reserved [RFC7313]
1 Invalid Message Length [RFC7313]
2-255 Unassigned
7. Security Considerations
Security considerations are given in [RFC4272] , but they do not
cover Route-Refresh and many other BGP extensions. This document
does not significantly change the underlying security issues
regarding Route-Refresh, although improved error handling may aid
operational security.
8. Acknowledgements
The authors would like to thank Pedro Marques, Pradosh Mohapatra,
Robert Raszuk, Pranav Mehta, Shyam Sethuram, Bruno Decraene, Martin
Djernaes, Jeff Haas, Ilya Varlashkin, Rob Shakir, Paul Jakma, Jie
Dong, Qing Zeng, Albert Tian, Jakob Heitz, and Chris Hall for their
review and comments. The authors would like to thank John Scudder
for the review and contribution to this document.
9. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2918] Chen, E., "Route Refresh Capability for BGP-4", RFC 2918,
September 2000.
[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, January 2006.
[RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis", RFC
4272, January 2006.
[RFC4724] Sangli, S., Chen, E., Fernando, R., Scudder, J., and Y.
Rekhter, "Graceful Restart Mechanism for BGP", RFC 4724,
January 2007.
[RFC5291] Chen, E. and Y. Rekhter, "Outbound Route Filtering
Capability for BGP-4", RFC 5291, August 2008.
[RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement
with BGP-4", RFC 5492, February 2009.
Authors' Addresses
Keyur Patel
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
USA
EMail: keyupate@cisco.com
Enke Chen
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
USA
EMail: enkechen@cisco.com
Balaji Venkatachalapathy
EMail: balaji_pv@hotmail.com
AI ELI5
On this page
§1Why Route Refresh Needs Markers
BGP speakers sometimes need to validate routing consistency, for example to catch a missing route withdrawal. The RFC says such checks usually involve offline, manual operations that are tedious and time-consuming.
RFC 2918 already lets a speaker ask a peer to re-advertise its routes. Route refresh, as this RFC uses the term, is the complete re-advertisement of the Adj-RIB-Out to a peer, subject to routing policies. What it lacks is a way to say where that re-advertisement begins and ends. This RFC adds that, so validation can be done online and non-disruptively.
When a friend resends a long list, you cannot tell when they are done. This RFC makes them say 'start' and 'end' so you know.
§2The New Capability and Message Subtypes
The Enhanced Route Refresh Capability is a new BGP capability, using the mechanism of RFC 5492. IANA assigned it Capability Code 70, and its Capability Length is zero. Advertising it tells a peer that the speaker supports the message subtypes and procedures in this RFC.
The Reserved field of the ROUTE-REFRESH message from RFC 2918 is redefined as the Message Subtype. A speaker that supports the procedures SHOULD advertise the capability, and the procedures apply only once a speaker has received the capability from a peer.
Two routers first tell each other 'I know the start and end trick'. Only then do they use it.
§3Message Subtypes
The redefined field takes these values:
0: a normal route refresh request, with or without Outbound Route Filtering (RFC 5291).1: BoRR, the demarcation of the beginning of a route refresh.2: EoRR, the demarcation of the ending of a route refresh.255: Reserved.
All other values are reserved for future use. A speaker that gets a ROUTE-REFRESH message with a subtype other than 0, 1 or 2 MUST ignore it and SHOULD log an error.
The message gets a small label: 'please resend', 'I am starting to resend' or 'I am done resending'.
- 0Route-Refresh — Normal route refresh request, with or without ORF.
- 1BoRR — Marks the beginning of a route refresh.
- 2EoRR — Marks the ending of a route refresh.
- 255Reserved — Reserved.
§4How a Refresh Works
Before a speaker starts a route refresh, whether it started locally or answers a normal request from the peer, it MUST send a BoRR message. After it finishes re-advertising the entire Adj-RIB-Out, it MUST send an EoRR message. The 'entire' Adj-RIB-Out means all route entries at the start of the operation, covering both reachability and unreachability information. If an entry changes later, only that entry needs to be advertised.
A BoRR can arrive at any time. On receiving one, the speaker MUST mark all routes from that peer for the given AFI and SAFI pair as stale. Routes that arrive in the re-advertisement replace the matching stale routes. On receiving an EoRR, the speaker MUST immediately remove any routes from that peer still marked stale for that pair, and MAY log them for analysis.
A speaker MAY ignore an EoRR that arrives without a prior BoRR. An implementation MAY also set a locally configurable upper bound on how long stale routes are kept, and remove them without waiting for the EoRR once it is reached.
When you hear 'start', you put a sticky note on every item you have. Each item that comes again loses its note. At 'end', whatever still has a note gets thrown away.
- ROUTE-REFRESH (0)A normal request. A refresh may also start locally.
- BoRR (1)Receiver marks routes for the AFI/SAFI as stale.
- Adj-RIB-Out routesEach route replaces its stale copy.
- EoRR (2)Receiver removes routes still stale.
§5Working with Graceful Restart
The RFC keeps this feature separate from the End-of-RIB (EoR) marker in Graceful Restart (RFC 4724), so that stale routes are not cleaned up too early.
- A speaker that supports Graceful Restart MUST NOT send a BoRR for an AFI and SAFI before it sends the EoR for that pair to the neighbor.
- A speaker that has received the Graceful Restart Capability from its neighbor MUST ignore any BoRR for a pair received before it gets the EoR for that pair, and SHOULD log an error.
There is already an 'I finished my first list' signal for restarts. This rule makes sure the two kinds of 'finished' do not get mixed up.
§6Error Handling
The RFC defines a new NOTIFICATION error code, 7, named ROUTE-REFRESH Message Error, with one subcode: 1, Invalid Message Length. These rules apply only when the speaker has received the Enhanced Route Refresh Capability from the peer.
If the length of a received ROUTE-REFRESH message with subtype 1 or 2 is not 4, excluding the fixed-size message header, the speaker MUST send a NOTIFICATION with that error code and subcode. The Data field MUST contain the complete ROUTE-REFRESH message.
If a start or end note is the wrong size, the receiver sends back a complaint that includes the bad note.
§7IANA Registries
IANA assigned Capability Code 70 in the Capability Codes registry. It created a new registry, 'BGP Route Refresh Subcodes', where values 0-127 need Standards Action and values 128-254 are First Come First Served. Values 3-254 are unassigned.
IANA also renamed the 'BGP Error Codes' registry to 'BGP Error (Notification) Codes', allocated the new error code, and created the registry 'BGP ROUTE-REFRESH Message Error subcodes', where 0 is Reserved, 1 is Invalid Message Length and 2-255 are unassigned.
A public list of numbers was updated so everyone uses the new codes the same way.