Network Working Group P. Mohapatra
Internet-Draft A. Sreekantiah
Intended status: Standards Track K. Patel
Expires: July 21, 2012 B. Pithawala
Cisco Systems
A. Lo
Arista Networks
January 18, 2012
Automatic Route Target Filtering for legacy PEs
draft-ietf-idr-legacy-rtc-00
Abstract
This document describes a simple procedure that allows "legacy" BGP
speakers to exchange route target membership information in BGP
without using mechanisms specified in RFC 4684. The intention of the
proposed technique is to help in partial deployment scenarios and is
not meant to replace RFC 4684.
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
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This Internet-Draft will expire on July 21, 2012.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Basic Idea . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Detailed Operation . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Legacy PE Behavior . . . . . . . . . . . . . . . . . . . . 4
3.2. RR behavior . . . . . . . . . . . . . . . . . . . . . . . 7
3.2.1. Generating Route Target Membership NLRIs for the
legacy PE clients . . . . . . . . . . . . . . . . . . 7
4. ROUTE_FILTER community . . . . . . . . . . . . . . . . . . . . 8
5. Deployment Considerations . . . . . . . . . . . . . . . . . . 8
6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 9
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
9. Security Considerations . . . . . . . . . . . . . . . . . . . 9
10. Normative References . . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
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1. Introduction
[RFC4684], "Constrained Route Distribution for Border Gateway
Protocol/ MultiProtocol Label Switching (BGP/MPLS) Internet Protocol
(IP) Virtual Private Networks (VPNs)" provides a powerful and general
means for BGP speakers to exchange and propagate Route Target
reachability information and constrain VPN route distribution to
achieve high scale. However, it requires that all the BGP speakers
in the network are upgraded to support this functionality. For
example, in a network with route reflectors (RR), if one PE client in
the cluster doesn't support constrained distribution, the cluster
degenerates into storing and processing all the VPN routes. The
route reflectors need to request and store all the network routes
since they do not receive route target membership information from
the legacy PEs. The RR will also generate all those routes to the
legacy PEs and the legacy PEs will end up filtering the routes and
store the subset of VPN routes that are of interest.
This document specifies a mechanism for such legacy PE devices using
existing configuration and toolset to provide similar benefits as
[RFC4684]. At the same time, it is backward-compatible with the
procedures defined in [RFC4684]. It also allows graceful upgrade of
the legacy router to be [RFC4684] capable.
1.1. 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 RFC 2119 [RFC2119].
2. Basic Idea
The basic idea is to make use of VPN unicast route exchange from the
legacy PEs to a new BGP speaker (e.g. an RR) to signal RT membership.
The legacy PEs announce a set of "special" routes with mapped RTs to
the RR along with a standard community (defined in this document).
The presence of the community triggers the RR to extract the RTs and
build RT membership information.
3. Detailed Operation
3.1. Legacy PE Behavior
The following simple steps are performed on the legacy PE device:
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o Collect the "import route targets" of all the configured customer
VRFs. Let's call this set 'IRTS'.
o Create a special "route-filter VRF" with a route distinguisher(RD)
that's configured with the same value across the network for all
legacy PE devices. Note: the equivalence of the RD value is for
optimization - the operator may choose to use different values.
o Originate one or more routes in this VRF and attach a subset of
'IRTS' as "translated route-target extended communities" with each
route so as to evenly distribute the RTs (and to make sure they
can fit into one BGP UPDATE message). Collectively, the union of
the "translated route-target extended communities" of all these
routes is equal to the set 'IRTS'. The translated RTs are
attached as export route-targets for the routes originated in the
route-filter VRF.
o The translation of the IRTs is necessary in order to refrain from
importing "route-filter" VRF routes into VPN VRFs that would
import the same route-targets. The translation of the IRTS is
done as follows. For a given IRT, the equivalent translated RT
(TRT) is constructed by means of swapping the value of the high-
order octet of the Type field for the IRT (as defined in
[RFC4360]).
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0 1 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x00 | 0x02 | | 0x01 | 0x02 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|2B AS | |2B AS => IP(high) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<=>+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Local Admin(high) | |Local Admin(high) => IP(low) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Local Admin(low) | |Local Admin(low) => Local Admin|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x01 | 0x02 | | 0x02 | 0x02 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|IP(high) | |IP(high) => 4B AS(high) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<=>+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|IP(low) | |IP(low) => 4B AS(low) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Local Admin | |Local Admin => Local Admin |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x02 | 0x02 | | 0x00 | 0x02 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|4B AS(high) | |4B AS(high) => 2B AS |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<=>+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|4B AS(low) | |4B AS(low) => Local Admin(high)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Local Admin | |Local Admin => Local Admin(low)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
As an example, if IRT R= 65500:12244(hex: 0x0002ffdc00002fd4),
equivalent route-filter TRT: 255.220.0.0:12244(hex:
0x0102ffdc00002fd4). One shortcoming of the translation mechanism
is a possible collision between IRTs and TRTs if the network has
been configured with RTs of multiple higher order octet types
(2-byte AS, IP address, and 4-byte AS). It is expected that such
a configuration is rare in practice.
o As an alternative to the translation of the IRTS, the subset of
the 'IRTS' can be attached as-is (without swapping the type field
as described earlier) as "export route-target extended
communities" with each route so as to evenly distribute the RTs
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(and to make sure they can fit into one BGP UPDATE message). In
this case, the IRT subsets can be attached in outbound policy to
avoid the route-filter VRFs from being imported into VPN VRFs.
Also in this case, the route-filter VRF routes must be tagged with
a different special community (from that associated with the
translated RTs) as described in Section 4 so that the receiving
BGP speaker can distinguish the two cases.
o The routes are marked with NO_ADVERTISE and NO_EXPORT well-known
communities as well as the appropriate new community that's
defined in this document Section 4. Note that there is no
specific provision made to disallow configuration of subsequent
route policies that can potentially alter the set of communities
attached to "route-filter" VRF routes. The protocol behavior in
such a case is undefined and the use of those policy statements is
discouraged.
3.2. RR behavior
Upon receiving the "route-filter" routes, the BGP speaker does its
usual processing to store them in its local RIB. It recognizes them
as route-filter routes based on the association of the new standard
community as defined in this document. If required (as indicated by
the community value), it translates the attached route-target
extended communities (TRT) to equivalent import route-targets (IRT).
Finally it creates the route-target filter list for each legacy
client by collecting the entire set of route targets. From this
point onwards, the behavior is similar to that defined in [RFC4684].
The RR does not propagate the routes further because of their
association with NO_ADVERTISE community. Also the VPN EoR that is
sent by the legacy PE should also be used as an indication that the
legacy PE is done sending the route-filter information as per the
procedures defined in [RFC4684] for implementing a EoR mechanism to
signal the completion of initial RT membership exchange.
3.2.1. Generating Route Target Membership NLRIs for the legacy PE
clients
The RR MAY also translate the received extended communities from
legacy clients into route target membership NLRIs as if it had
received those NLRIs from the client itself. This is useful for
further propagation of the NLRIs to rest of the network to create RT
membership flooding graph. When the route_filter routes are received
with same RD (from all legacy PE speakers), processing of the paths
to generate equivalent NLRIs becomes fairly easy.
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4. ROUTE_FILTER community
This memo defines four BGP communities that are attached to BGP
UPDATE messages at the legacy PE devices and processed by the route
reflectors as defined above. They are as follows:
+----------------------------+--------------------------------------+
| Community | Meaning |
+----------------------------+--------------------------------------+
| ROUTE_FILTER_v4 | RTs are attached as-is for VPNv4 |
| | route filtering |
| ... | ... |
| ROUTE_FILTER_v6 | RTs are attached as-is for VPNv6 |
| | route filtering |
| ... | ... |
| ROUTE_FILTER_TRANSLATED_v4 | Translated RTs are attached for |
| | VPNv4 route filtering |
| ... | ... |
| ROUTE_FILTER_TRANSLATED_v6 | Translated RTs are attached for |
| | VPNv6 route filtering |
+----------------------------+--------------------------------------+
In the absence of (or lack of support of) AF specific communities
(ROUTE_FILTER_v6, ROUTE_FILTER_TRANSLATED_v6), the ROUTE_FILTER_v4 or
ROUTE_FILTER_TRANSLATED_v4 MAY be treated by an implementation as a
default VPN route-filter community to build a combination VPN filter
for all VPN AFs (VPNv4, VPNv6) present on the RR. This is in
accordance with the procedures in [RFC4684] to build combination
route-filters for VPN AFs and AF specific route-filters defined in
[I-D.keyur-bgp-af-specific-rt-constrain]. If this is the case, then
subsequent receipt of any "route-filter" routes with AF specific
communities (ROUTE_FILTER_v6, ROUTE_FILTER_TRANSLATED_v6) will
override the default filters sent with ROUTE_FILTER_v4 or
ROUTE_FILTER_TRANSLATED_v4 for the VPNv6 AFI when support for the AF
specific communities exists.
5. Deployment Considerations
When both the legacy PE and the RR support extended community based
Outbound Route Filtering as in
[I-D.draft-chen-bgp-ext-community-orf-00] this may be used as a
alternate solution for the legacy PE to signal RT membership
information, in order to realize the same benefits as [RFC4684].
Also extended community ORF can be used amongst the RRs in lieu of
[RFC4684] to realize similar benefits.
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6. Contributors
Significant contributions were made by Stephane Litkowski, Luis M
Tomotaki and James Uttaro which the authors would like to
acknowledge.
7. Acknowledgements
The authors would like to thank Rob Shakir for his review and
comments.
8. IANA Considerations
IANA shall assign new code points from BGP first-come first-serve
communities for the four communities as listed in Section 4.
9. Security Considerations
None.
10. Normative References
[]
Chen, E. and Y. Rekhter, "Extended Community Based
Outbound Route Filter for BGP-4",
draft-chen-bgp-ext-community-orf-00 (work in progress),
June 2006.
[I-D.keyur-bgp-af-specific-rt-constrain]
Patel, K., Raszuk, R., Djernaes, M., Dong, J., and M.
Chen, "AFI Specific Route Target Distribution",
draft-keyur-bgp-af-specific-rt-constrain-00 (work in
progress), October 2010.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, January 2006.
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, February 2006.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
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Networks (VPNs)", RFC 4364, 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.
Authors' Addresses
Pradosh Mohapatra
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
USA
Email: pmohapat@cisco.com
Arjun Sreekantiah
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
USA
Email: asreekan@cisco.com
Keyur Patel
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
USA
Email: keyupate@cisco.com
Burjiz Pithawala
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
USA
Email: bpithaw@cisco.com
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Alton Lo
Arista Networks
5470 Great America Parkway
Santa Clara, CA 95054
USA
Email: altonlo@aristanetworks.com
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