Internet DRAFT - draft-ietf-idr-rtc-no-rt
draft-ietf-idr-rtc-no-rt
IDR Working Group E. Rosen
Internet-Draft Unaffiliated
Updates: 4684 (if approved) K. Patel
Intended status: Standards Track Arccus
Expires: April 3, 2020 J. Haas, Ed.
Juniper Networks, Inc.
R. Raszuk
Bloomberg LP
October 1, 2019
Route Target Constrained Distribution of Routes with no Route Targets
draft-ietf-idr-rtc-no-rt-12.txt
Abstract
There are a variety of BGP-enabled services in which the originator
of a BGP route may attach one or more "Route Targets" to the route.
By means of a procedure known as "RT Constrained Distribution" (RTC),
a given BGP speaker (call it "B") can announce the set of RTs in
which it has interest. The implication is that if a particular route
(call it "R") carries any RTs at all, BGP speaker B wants to receive
route R if and only if B has announced interest in one of the RTs
carried by R. However, if route R does not carry any RTs at all,
prior specifications do not make it clear whether B's use of RTC
implies that it does not want to receive route R. This has caused
interoperability problems in the field, as some implementations of
RTC do not allow B to receive R, but some services presuppose that B
will receive R. This document updates RFC 4684 by clarifying 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.
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
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 3, 2020.
Rosen, et al. Expires April 3, 2020 [Page 1]
Internet-Draft RTC Behavior w/o RTs October 2019
Copyright Notice
Copyright (c) 2019 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. 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 . . . . . . . . . . . . . . . . . 6
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.
If RTC is enabled on a particular BGP session, the session must be
provisioned with the set of "address family" and "subsequent address
family" values (AFI/SAFIs) to which RTC is to be applied. In
[RFC4684] it is implicitly assumed that RTC will only be applied to
AFI/SAFIs for which all the routes carry RTs. When this assumption
Rosen, et al. Expires April 3, 2020 [Page 2]
Internet-Draft RTC Behavior w/o RTs October 2019
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 AFI/SAFIs 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 possible 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 not
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". 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 existing AFI/SAFIs. This
default behavior ensures proper operation when RTC is applied to an
existing AFI/SAFI. The default behavior may of course be overridden
by 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.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
Rosen, et al. Expires April 3, 2020 [Page 3]
Internet-Draft RTC Behavior w/o RTs October 2019
2. Some Deployment Scenarios
The lack of a clearly defined default behavior for applying RTC to
routes that carry no RTs is problematic in at least three scenarios.
o [RFC6037] describes a deployed Multicast VPN (MVPN) solution. It
defines a BGP SAFI known as "MDT-SAFI". Routes with this SAFI may
carry RTs, but are not required to do so. In order for the
procedures of [RFC6037] 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 SHOULD be constrained by RTC.
o [RFC7716] specifies a way to provide "Global Table Multicast" (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 SAFI 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 routes to carry RTs. In order
for the procedures of [RFC7716] 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 (or the Global
Table Multicast service mentioned above). 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 2, this
document specifies a default behavior for the case where RTC is
applied to a particular 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, [RFC6037]), the default behavior
Rosen, et al. Expires April 3, 2020 [Page 4]
Internet-Draft RTC Behavior w/o RTs October 2019
MUST be 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 the
MCAST-VPN address family (SAFI=5, [RFC6514], [RFC7716]), the default
behavior MUST be 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 MUST be 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
The security considerations of [RFC4684] apply.
The procedures of this document may allow the distribution of certain
SAFI-5 and SAFI-66 routes, in situations where some implementations
of RTC would previously have prevented their distribution. However,
it is necessary to distribute such routes in order for the
applications using them to operate properly. Allowing the
distribution of such routes does not create any new security
considerations beyond those of the applications that use the routes.
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, <https://www.rfc-
editor.org/info/rfc2119>.
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
February 2006, <https://www.rfc-editor.org/info/rfc4360>.
Rosen, et al. Expires April 3, 2020 [Page 5]
Internet-Draft RTC Behavior w/o RTs October 2019
[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, DOI 10.17487/RFC4684,
November 2006, <https://www.rfc-editor.org/info/rfc4684>.
6.2. Informative References
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
2006, <https://www.rfc-editor.org/info/rfc4364>.
[RFC6037] Rosen, E., Ed., Cai, Y., Ed., and IJ. Wijnands, "Cisco
Systems' Solution for Multicast in BGP/MPLS IP VPNs",
RFC 6037, DOI 10.17487/RFC6037, October 2010,
<https://www.rfc-editor.org/info/rfc6037>.
[RFC6513] Rosen, E., Ed. and R. Aggarwal, Ed., "Multicast in MPLS/
BGP IP VPNs", RFC 6513, DOI 10.17487/RFC6513, February
2012, <https://www.rfc-editor.org/info/rfc6513>.
[RFC6514] Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
Encodings and Procedures for Multicast in MPLS/BGP IP
VPNs", RFC 6514, DOI 10.17487/RFC6514, February 2012,
<https://www.rfc-editor.org/info/rfc6514>.
[RFC7716] Zhang, J., Giuliano, L., Rosen, E., Ed., Subramanian, K.,
and D. Pacella, "Global Table Multicast with BGP Multicast
VPN (BGP-MVPN) Procedures", RFC 7716,
DOI 10.17487/RFC7716, December 2015, <https://www.rfc-
editor.org/info/rfc7716>.
Authors' Addresses
Eric C. Rosen
Unaffiliated
Email: erosen52@gmail.com
Keyur Patel
Arccus
Email: keyur@arccus.com
Rosen, et al. Expires April 3, 2020 [Page 6]
Internet-Draft RTC Behavior w/o RTs October 2019
Jeffrey Haas (editor)
Juniper Networks, Inc.
1133 Innovation Way
Sunnyvale, California 94089
United States
Email: jhaas@juniper.net
Robert Raszuk
Bloomberg LP
731 Lexington Ave
New York City, NY 10022
United States
Email: robert@raszuk.net
Rosen, et al. Expires April 3, 2020 [Page 7]
