Internet DRAFT - draft-ietf-idr-rtc-hierarchical-rr
draft-ietf-idr-rtc-hierarchical-rr
Network Working Group J. Dong
Internet-Draft M. Chen
Intended status: Standards Track Huawei Technologies
Expires: 5 September 2024 R. Raszuk
Arrcus
4 March 2024
Extensions to RT-Constrain in Hierarchical Route Reflection Scenarios
draft-ietf-idr-rtc-hierarchical-rr-04
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 guarantee a correct route
distribution graph. This document describes the problem scenario and
proposes a solution to address the RT-Constrain issue in 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
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
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 5 September 2024.
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Copyright Notice
Copyright (c) 2024 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
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 2
3. Potential Solutions . . . . . . . . . . . . . . . . . . . . . 3
3.1. Add-path Based Solution . . . . . . . . . . . . . . . . . 4
3.2. Disjoint Alternate Path Solution . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
The Route Target (RT) Constrain mechanism specified in [RFC4684] 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 advertisment rules of RT membership information as defined
in section 3.2 of [RFC4684] cannot guarantee a correct route
distribution graph.
This document describes the problem scenario and proposes a solution
to address the RT-Constrain issue in hierarchical RR scenarios.
2. Problem Statement
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+---------------------------------+
| +----+ |
| 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
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, here assume the
route received from RR-2 is selected by RR-1 as the best route. Then
RR-1 needs to advertise the best RT-Constrain route 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 it will not advertise the
VPN routes of VPN-1 to RR-1.
3. Potential Solutions
This document specifies 2 potential solutions for the RTC issue in
hierarchical RR scenario. In a later revision, one solution will to
be selected based on the decision of the IDR working group.
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3.1. Add-path Based Solution
This section provides one possible solution which is based on the
add-path mechanism defined in [RFC7911]. It makes use of the add-
path mechanism for RTC route advertisement between the hierarchical
RRs. The solution is summerized as follows:
* The route-reflector clients which themselves are also route-
reflectors SHOULD be identified, then BGP add-paths [RFC7911]
SHOULD be enabled for RT membership NLRI on the BGP sessions
between the higher layer RR and the lower layer RRs to ensure that
sufficient RT-Constrain routes can be advertised by the higher
layer RR to the lower layer RRs to pass BGP loop detection. In
this case normal BGP path advertisement rules as defined in
[RFC4271] SHOULD be applied. The number of RT-Constrain routes to
be advertised with add-path mechanism is a local decision of
operators. To ensure that sufficient RT-Constrain routes are
advertised to build the distribution graph, the recommended add-
path number is the maximum number of the BGP client sessions in
the same cluster plus 1.
* When advertising an RT membership NLRI to a route-reflector client
which is not a lower layer RR, the advertisement rule as defined
in section 3.2 of [RFC4684] SHOULD be applied.
With the above advertisement rule, RR-1 in figure 1 SHOULD advertise
to RR-2 the RT-Constrain routes received from both RR-2 and RR-3,
then the RTC route from RR-3 will pass the BGP loop detection on RR-
2, thus the route distribution graph can be set up correctly.
3.2. Disjoint Alternate Path Solution
This section specifies another possible solution which proposes some
modification to the intra-AS advertisement rule of RTC route.
Since the advertisement of RT-Constrain route is to set up a route
distribution graph and not to guide the data packet forwarding,
actually all the available RT-Constrain routes should be considered
in setting up the route distribution graph, not just the best one.
Thus the following advertisment rule for RT membership information is
proposed to replace the rule i and ii in section 3.2 of [RFC4684]:
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* When advertising an RT membership NLRI to a route-reflector peer
(either client or non-client), if the best path as selected by the
path selection procedure described in Section 9.1 of [RFC4271] is
the path received from this peer, and there are alternative paths
received from other peers, then the most disjoint alternative
route SHOULD be advertised to this peer. The most disjoint
alternative path is the path whose CLUSTER_LIST and ORIGINATOR_ID
attributes are diverse from the attributes of the best path.
With the above advertisement rule, RR-1 in figure 1 would advertise
to RR-2 the RT-Constrain route received from RR-3, which is the most
disjoint alternative route compared with the best route received from
RR-2. In this way, RR-2 will not discard the RT-constrain route
received from RR-1, and the route distribution graph can be set up
correctly.
4. IANA Considerations
This document makes no request of IANA.
5. Security Considerations
This document does not change the security properties of BGP based
VPNs and [RFC4684].
6. Acknowledgements
The authors would like to thank Yaqun Xiao for the discussion of RT-
Constrain issue in hierarchical RR scenario. Many people have made
valuable comments and suggestions, including Susan Hares, Jeffrey
Haas, Stephane Litkowski, Vitkovský Adam, Xiaohu Xu, Uttaro James,
Shyam Sethuram, Saikat Ray and Bruno Decraene.
7. References
7.1. 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>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.
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[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>.
7.2. Informative References
[RFC7911] Walton, D., Retana, A., Chen, E., and J. Scudder,
"Advertisement of Multiple Paths in BGP", RFC 7911,
DOI 10.17487/RFC7911, July 2016,
<https://www.rfc-editor.org/info/rfc7911>.
Authors' Addresses
Jie Dong
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing
100095
China
Email: jie.dong@huawei.com
Mach(Guoyi) Chen
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing
100095
China
Email: mach.chen@huawei.com
Robert Raszuk
Arrcus
Email: robert@raszuk.net
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