Network Working Group J. Dong
Internet-Draft M. Chen
Intended status: Standards Track Huawei Technologies
Expires: December 21, 2014 June 19, 2014
Extensions to RT-Constrain in Hierarchical Route Reflection Scenarios
draft-dong-idr-rtc-hierarchical-rr-00
Abstract
The Route Target (RT) Constrain mechanism specified in RFC 4684 is
used to build a route distribution graph in order to restrict the
propagation of Virtual Private Network (VPN) routes. In network
scenarios where hierarchical route reflection (RR) is used, the
existing RT-Constrain mechanism cannot build a correct route
distribution graph. This document refines the route distribution
rules of RT-Constrain to address the hierarchical RR scenarios.
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].
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on December 21, 2014.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Internet-Draft RT-Constrain in Hierarchical RR Scenario June 2014
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Proposed Solution . . . . . . . . . . . . . . . . . . . . . . 3
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . 4
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
6. Normative References . . . . . . . . . . . . . . . . . . . . 4
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 4
1. Introduction
The Route Target (RT) Constrain mechanism specified in RFC 4684 is
used to build a route distribution graph in order to restrict the
propagation of Virtual Private Network (VPN) routes. In network
scenarios where hierarchical route reflection (RR) is used, the
existing RT-Constrain mechanism cannot build a correct route
distribution graph.
+---------------------------------+
| +----+ |
| Clu-1 |RR-1| |
| /+----+\ |
| / \ |
| +----+ +----+ |
| Clu-2 |RR-2| |RR-3| Clu-3 |
| +-/--+ +/--\+ |
| / / \ |
| +----+ +----+ +----+ |
| |PE-1| |PE-2| |PE-3| |
| +----+ +----+ +----+ |
| | | | |
+-------|----------|---------|----+
RT-1 | RT-1 | | RT-1
+--------+ +--------+ +--------+
| VPN-1 | | VPN-1 | | VPN-1 |
+--------+ +--------+ +--------+
Figure 1. RT-Constrain with Hierarchical RR
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As shown in Figure 1, hierarchical RRs are deployed in the network,
RR-2 and RR-3 are route-reflectors of their connecting PEs, and are
also the clients of RR-1. If each PE advertises RT membership
information of RT-1 to the upstream RR, after the best path
selection, both RR-2 and RR-3 would create the CLUSTER_LIST
attribute, prepend their local CLUSTER_ID and then advertise the best
path to RR-1 and their clients respectively.
On receipt of the RT-Constrain routes from RR-2 and RR-3, RR-1 will
select one of the received routes as the best route, assume the route
received from RR-2 is selected by RR-1 as the best path. Then RR-1
needs to advertise the best path to both RR-2 and RR-3 to create the
route distribution graph of VPN-1. RR-1 would prepend its CLUSTER_ID
to the CLUSTER_LIST of the path, and according to the rules in
Section 3.2 of [RFC4684], it sets the ORIGINATOR_ID to its own
router-id, and the NEXT_HOP to the local address for the session.
Then RR-1 would advertise this route to both RR-2 and RR-3. On
receipt of the RT-Constrain route from RR-1, RR-2 checks the
CLUSTER_LIST and find its own CLUSTER_ID in the list, so this route
will be ignored by RR-2. As a result, RR-2 will not form the
outbound filter of RT-1 towards RR-1, hence will not advertise VPN
routes with RT-1 to RR-1.
2. Proposed Solution
The problem described in the above section is that the best path is
sent back to the BGP speaker which advertised the path and get
discarded due to the BGP loop detection mechanisms. Since the
advertisement of RT-Constrain route is to set up a route distribution
graph and not to guide the data packet forwarding, all the available
paths can be considered in setting up the route distribution graph,
not just the best path. Thus in addition to the rules specified in
section 3.2 of [RFC4684], the following rule applies in the
advertisement of RT-Constrain routes:
o When advertising an RT membership NLRI to a route-reflector
client, if the best route as selected by the path selection
procedure described in Section 9.1 of [RFC4271] is the path
received from this client, and there are alternative paths
received from other peers, the most disjoint alternative route
SHOULD be advertised to that client; The most disjoint alternative
path is the path whose CLUSTER_LIST and ORIGINATOR_ID attributes
are different from the attributes of the best path.
With this additional rule, RR-1 in Figure 1 would advertise to RR-2
the RT-Constrain route received from RR-3, although the best route is
received from RR-2. Thus RR-2 will not discard the RT-constrain
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route received from RR-1, and the route distribution graph can be set
up completely.
3. IANA Considerations
This document makes no request of IANA.
4. Security Considerations
This document does not change the security properties of BGP based
VPNs and [RFC4684].
5. Acknowledgements
The authors would like to thank Yaqun Xiao for the discussion about
RT-Constrain in hierarchical RR scenario.
6. Normative References
[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.
[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
Jie Dong
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
Email: jie.dong@huawei.com
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Mach(Guoyi) Chen
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
Email: mach.chen@huawei.com
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