Internet DRAFT - draft-fletcher-bgp-inactive-path
draft-fletcher-bgp-inactive-path
Network Working Group Justin Fletcher
Internet Draft Proficient Networks
Expiration Date: July 2003
Inactive Path Advertisement in BGP-4
draft-fletcher-bgp-inactive-path-00.txt
Status of this Memo
This document is an Internet-Draft and is subject to all provisions
of Section 10 of RFC2026.
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Abstract
This document defines BGP capabilities and a path attribute to permit
advertisement of routes other than those selected during the BGP
decision process. These extensions would provide additional routing
information for research, monitoring and policy decisions.
1. Introduction
BGP [BGP-4] as currently defined advertises only routes to BGP peers
selected through the decision process. These advertised routes,
known as the active path, provide an incomplete view of a BGP peer's
knowledge of network adjacency; additional routes may be present in
the Adj-RIBs-In which have not been selected by the decision process,
otherwise known as the inactive path. Advertisement of a peer's
complete set of active and inactive paths will provide additional
information for route servers, research, monitoring and policy
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decisions.
The INACTIVE_PATH Path Attribute and Inactive Path Capabilities are
defined to identify advertised routes on an inactive path and routers
capable of processing such routes.
A potential application in a production network would be for a
provider to selectively advertise as inactive paths a customer's CIDR
ranges back to them. This would allow the customer to see advertised
routes after provider processing for troubleshooting purposes.
Outbound filtering may be applied to constrain the visibility of
specific attributes.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2. Path Attribute
INACTIVE_PATH is an optional non-transitive attribute of length 0;
the type code for this attribute is specified in the "IANA
Considerations" section of this document.
It is used by a BGP speaker to inform other BGP speakers that the
advertised route is not advertised as a result of the BGP decision
process. As such, it MUST NOT be considered in the listener's
decision process and MUST NOT be re-advertised.
3. Inactive Path Capabilities
The Inactive Path Capabilities are two new BGP capabilities [BGP-
CAP]. The Capability Code for both of these Capabilities are
specified in the "IANA Considerations" section of this document. The
Capability Length field of both Capabilities is set to 0.
By advertising the Inactive Path Send Capability to a peer in the
OPEN, a BGP speaker informs the peer that the speaker is capable of
sending UPDATE messages containing routes with the INACTIVE_PATH
attribute set.
By advertising the Inactive Path Receive Capability to a peer in the
OPEN, a BGP speaker informs the peer that the speaker is capable of
processing UPDATE messages containing routes with the INACTIVE_PATH
attribute set.
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4. Configuration
When Inactive Path Capabilities are supported, a configuration option
MUST be provided specifying whether inactive path routes are to be
advertised or received on a per-peer basis. The default
configuration for this option MUST be to advertise or receive only
active path routes.
5. Route Advertisement
Routes are selected for advertisement through the BGP decision
process. When is option is enabled, the routes that were not
selected through the decision process are processed into the
associated Adj-RIBs-Out with the INACTIVE_PATH attribute set
including applicable filtering and route processing performed by the
BGP peer. Outbound filters are then applied and the resultant Adj-
RIBs-Out are advertised to the BGP peers.
Routes containing the INACTIVE_PATH attribute set MUST NOT be sent
unless the speaker has sent the Inactive Path Send Capability and the
listener has sent the Inactive Path Receive Capability in the
corresponding OPEN messages.
References
[BGP-4] Y. Rekhter, and T. Li, "A Border Gateway Protocol 4 (BGP-4)",
RFC 1771, March 1995.
[BGP-CAP] R. Chandra, J. Scudder, "Capabilities Advertisement with
BGP-4", RFC 2842, May 2000.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
Security Considerations
These extensions to BGP do not change the underlying security issues.
IANA Considerations
This document uses a BGP Capability Code to indicate that a BGP
speaker supports the Inactive Path Capability and a Attribute Type to
indicate an advertised inactive path. The Capability Code and
Attribute Type must be assigned by IANA per RFC 2842.
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Acknowledgments
The author would like to thank Robert Bays and Bruce Pinsky for
providing invaluable insight and expertise.
Author Information
Justin Fletcher
Proficient Networks
300 California
Suite 500
San Francisco, CA 94104
e-mail: jfletcher@proficient.net
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