Internet DRAFT - draft-rosen-idr-rtc-no-rt
draft-rosen-idr-rtc-no-rt
IDR Working Group E. Rosen, Ed.
Internet-Draft Juniper Networks, Inc.
Intended status: Standards Track K. Patel
Expires: April 19, 2015 Cisco Systems, Inc.
J. Haas
Juniper Networks, Inc.
R. Raszuk
October 16, 2014
Route Target Constrained Distribution of Routes with no Route Targets
draft-rosen-idr-rtc-no-rt-01.txt
Abstract
BGP routes sometimes carry an "Extended Communities" path attribute.
An Extended Communities path attribute can contain one or more "Route
Targets" (RTs). By means of a procedure known as "RT Constrained
Distribution" (RTC), a BGP speaker can send BGP UPDATE messages that
express its interest in a particular set of RTs. Generally, RTC has
been applied only to address families whose routes always carry RTs.
When RTC is applied to such an address family, a BGP speaker
expressing its interest in a particular set of RTs is indicating that
it wants to receive all and only the routes of that address family
that have at least one of the RTs of interest. However, there are
scenarios in which the originator of a route chooses not to include
any RTs at all, assuming that the distribution of a route with no RTs
at all will be unaffected by RTC. This has led to interoperability
problems in the field, where the originator of a route assumes that
RTC will not affect the distribution of the route, but intermediate
BGP speakers refuse to distribute that route because it does not
carry any RT of interest. The purpose of this document is to clarify
the effect of the RTC mechanism on routes that do not have any RTs.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on April 19, 2015.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Some Deployment Scenarios . . . . . . . . . . . . . . . . . . 4
3. Default Behavior . . . . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
6.1. Normative References . . . . . . . . . . . . . . . . . . 5
6.2. Informative References . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
A BGP route can carry a particular type of BGP path attribute known
as an "Extended Communities Attribute" [RFC4360]. Each such
attribute can contain a variable number of typed communities.
Certain typed communities are known as "Route Targets" (RTs)
([RFC4360], [RFC4364]).
[RFC4684] defines a procedure, known as "RT Constrained Distribution"
(RTC) that allows a BGP speaker to advertise its interest in a
particular set of RTs. It does so by advertising "RT membership
information". (See [RFC4684] for details.) It may advertise RT
membership for any number of RTs. By advertising membership for a
particular RT, a BGP speaker declares that it is interested in
receiving BGP routes that carry that RT.
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If RTC is enabled on a particular BGP session, the session must be
provisioned with the set of "address family" and "subsequent address
family" (AFI/SAFIs) values to which RTC is to be applied. In
[RFC4684] it is implicitly assumed that RTC will only by applied to
AFI/SAFIs where all the routes carry RTs. When this assumption is
true, the RTC semantics are clear. A BGP speaker advertising its
interest in RT1, RT2, ..., RTk is saying that, for the AFI/SAFIs to
which RTC is being applied, it is interested in any route that
carries at least one of those RTs, and it is not interested in any
route that does not carry at least one of those RTs.
However, [RFC4684] does not specify how the RTC procedures are to be
applied to address families whose routes sometimes carry RTs and
sometimes do not. Consider a BGP session between routers R1 and R2,
where R1 has advertised its interest in RT1, RT2, ..., RTk, and RTC
is being applied to a particular AFI/SAFI. Suppose R2 has a route of
that AFI/SAFI, and that route carries no RTs. Should R2 advertise
this route to R1 or not?
There are two different answers to this question, each of which seems
prima facie reasonable:
o No, R2 should not advertise the route, because it belongs to an
AFI/SAFI to which RTC is being applied, and the route does carry
any of the RTs in which R1 is interested.
o Yes, R2 should advertise the route; since the route carries no
RTs, the intention of the route's originator is that the
distribution of the route not be constrained by the RTC mechanism.
As might be expected, "one size does not fit all", and the best
answer depends upon the particular deployment scenario, and upon the
particular AFI/SAFI to which RTC is being applied.
Section 3 defines a default behavior for each existing AFI/SAFI.
This default behavior will ensure proper operation of that AFI/SAFI
when RTC is applied. The default behavior may of course be
overridden by a local policy.
Section 3 also defines a default "default behavior" for new AFI/
SAFIs. When a new AFI/SAFI is defined, the specification defining it
may specify a different default behavior; otherwise the default
default behavior will apply.
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2. Some Deployment Scenarios
There are at least three deployment scenarios where lack of a clearly
defined default behavior for RTC is problematic.
o [RFC6037] describes a deployed Multicast VPN (MVPN) solution. It
defines a BGP address family known as "MDT-SAFI". Routes of this
address family may carry RTs, but are not required to do so. In
order for the RFC6037 procedures to work properly, if an MDT-SAFI
route does not carry any RTs, the distribution of that route must
not be constrained by RTC. However, if an MDT-SAFI route does
carry one or more RTs, its distribution may be constrained by RTC.
o [GTM] specifies a way to provide "global table" (as opposed to
VPN) multicast, using procedures that are very similar to those
described in [RFC6513] and [RFC6514] for MVPN. In particular, it
uses routes of the MCAST-VPN address family that is defined in
[RFC6514]. When used for MVPN, each MCAST-VPN route carries at
least one RT. However, when used for global table multicast, it
is optional for certain MCAST-VPN route types to carry RTs. In
order for the procedures of [GTM] to work properly, if an MCAST-
VPN route does not carry any RTs, the distribution of that route
must not be constrained by RTC.
o Typically, Route Targets have been carried only by routes that are
distributed as part of a VPN service. However, it may be
desirable to be able to place RTs on non-VPN routes (e.g., on
unicast IPv4 or IPv6 routes) and then to use RTC to constrain the
delivery of the non-VPN routes. For example, if a BGP speaker
desires to receive only a small set of IPv4 unicast routes, and
the desired routes carry one or more RTs, the BGP speaker could
use RTC to advertise its interest in one or more of those RTs. In
this application, the intention would be that any IPv4 unicast
route not carrying an RT would be filtered. Note that this is the
opposite of the behavior needed for the other use cases discussed
in this section.
3. Default Behavior
In order to handle the use cases discussed in Section 3, this
document specifies a default behavior for the case where RTC is
applied to a particular address family (AFI/SAFI), and some (or all)
routes of that address family do not carry any RTs.
When RTC is applied, on a particular BGP session, to routes of the
MDT-SAFI address family (SAFI=66), the default behavior is that
routes that do not carry any RTs are distributed on that session.
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When RTC is applied, on a particular BGP session, to routes of the
MCAST-VPN address family (SAFI=5), the default behavior is that
routes that do not carry any RTs are distributed on that session.
When RTC is applied, on a particular BGP session, to routes of other
address families, the default behavior is that routes without any RTs
are not distributed on that session. This default "default behavior"
applies to all AFI/SAFIs for which a different default behavior has
not been defined.
A BGP speaker may be provisioned to apply a non-default behavior to a
given AFI/SAFI. This is a matter of local policy.
4. IANA Considerations
This document contains no actions for IANA.
5. Security Considerations
No security considerations are raised by this document beyond those
already discussed in [RFC4684].
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, February 2006.
[RFC4684] Marques, P., Bonica, R., Fang, L., Martini, L., Raszuk,
R., Patel, K., and J. Guichard, "Constrained Route
Distribution for Border Gateway Protocol/MultiProtocol
Label Switching (BGP/MPLS) Internet Protocol (IP) Virtual
Private Networks (VPNs)", RFC 4684, November 2006.
6.2. Informative References
[GTM] Zhang, J., Giulano, L., Rosen, E., Subramanian, K.,
Pacella, D., and J. Schiller, "Global Table Multicast with
BGP-MVPN Procedures", internet-draft draft-ietf-l3vpn-
mvpn-global-table-mcast-00, July 2014.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, February 2006.
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[RFC6037] Rosen, E., Cai, Y., and IJ. Wijnands, "Cisco Systems'
Solution for Multicast in BGP/MPLS IP VPNs", RFC 6037,
October 2010.
[RFC6513] Rosen, E. and R. Aggarwal, "Multicast in MPLS/BGP IP
VPNs", RFC 6513, February 2012.
[RFC6514] Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
Encodings and Procedures for Multicast in MPLS/BGP IP
VPNs", RFC 6514, February 2012.
Authors' Addresses
Eric C. Rosen (editor)
Juniper Networks, Inc.
10 Technology Park Drive
Westford, Massachusetts 01886
USA
Email: erosen@juniper.net
Keyur Patel
Cisco Systems, Inc.
170 Tasman Drive
San Jose, California 95134
US
Email: keyupate@cisco.com
Jeffrey Haas
Juniper Networks, Inc.
1194 N. Mathilda Ave.
Sunnyvale, California 94089
US
Email: jhaas@juniper.net
Robert Raszuk
Email: robert@raszuk.net
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