Internet DRAFT - draft-anup-idr-bgp-duplicate-rt
draft-anup-idr-bgp-duplicate-rt
Inter-Domain Routing T. Kumar
Internet-Draft Ericsson
Intended status: Standards Track May 23, 2017
Expires: November 24, 2017
Procedures to handle duplicate Route Targets (RT) received by a BGP
Speaker
draft-anup-idr-bgp-duplicate-rt-00
Abstract
This document describes why duplicate suppression should not be
applied to BGP Route Target (RT) Address Family. It also explains
the problems incurred if duplicate suppression is applied to BGP
route constraints AF
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
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This Internet-Draft will expire on November 24, 2017.
Copyright Notice
Copyright (c) 2017 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Summary of the Problem . . . . . . . . . . . . . . . . . 3
3. Problem scenario - An Example . . . . . . . . . . . . . . . . 3
4. Existing workaround for the above problem . . . . . . . . . . 4
5. Solution to the Problem . . . . . . . . . . . . . . . . . . . 4
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 4
7. Security Considerations . . . . . . . . . . . . . . . . . . . 4
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 5
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
10.1. Normative References . . . . . . . . . . . . . . . . . . 5
10.2. Informative References . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
Address families like ipv4 unicast are used for exchange of routing
or reachability information. Receipt of an ipv4 unicast update by
router R means that the peer has the ipv4 route and hence, has sent
it to R, while the receiving router R computes bestpath and uses the
route for forwarding.
With respect to receiving ipv4 unicast update, we have two
possibilities:
1) The receiving router does not have the original route in its
database. It treats the update as fresh update. So, the received
ipv4 unicast update is processed and downloaded for forwarding.
2) The receiving router already has the route in its database. It
treats the update as duplicate and drops it. It is guaranteed by
BGP base protocol that the receiver had processed and
installed the route when the earlier update was seen, and hence it
can drop the duplicate ipv4 unicast update. Even if the duplicate
is processed again and installed again, there is no problem with
duplicate processing and installation.
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2. Problem
This section explains the problem when duplicate suppression is
applied to BGP updates carrying Route Targets (RT) Address Family
information.
RT address family is used to exchange VPN subscription information.
Receipt of an RT update means that the sender is interested in
getting vpn routes from this router. This router is expected to send
matching vpn routes in response. Which means, receipt of an RT
update, unlike ipv4 unicast update, does not end with local
installation of route, but also necessarily entails sending vpn
routes in response.
Like before, we have two cases to analyze with respect to receiving
duplicate RT updates:
1) The receiving router does not have earlier RT in its database.
It treats the RT as fresh update, and it sends vpn routes in
response.
2) The receiving router already has the RT in its database. It
treats the incoming RT as duplicate and drops it. But, when the
receiver gets the duplicate RT, whether the sender has vpn routes
or not, is not known at the receiver side. So, dropping the
duplicate RT without sending vpn routes in response, is a problem.
2.1. Summary of the Problem
When a duplicate RT is received, it is not guaranteed that the sender
of the RT has the required vpn routes. So the receiver cannot choose
to ignore an RT as duplicate, because unlike Ipv4 unicast route, an
RT indicates a subscription or a want of vpn routes and the receiver
does not know whether the sender has the vpn routes or not.
3. Problem scenario - An Example
First time when the import RT is configured the sender will not
have vpn routes, and it sends the RT to its peers, thereby
conveying its want of vpn routes.
The receiver also sees this RT coming from the sender for the
first time, and It sends vpn routes in response to the sender of
the RT.
Now, certain Destructive operations can lead to cleanup of vpn
routes. Example: Remove and add of vpn configurations, 'without'
affecting bgp peer session state.
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Here, due to removal of vpn config, the sender will cleanup the
vpn routes.
Then, due to quick addition of vpn config, the sender will request
for vpn routes by sending all the configured RTs.
But, the receiver still has the earlier RTs that was sent by the
peer. So, the receiver treats the RTs as duplicate and drops
them.
Thus no vpn routes are sent to the sender
4. Existing workaround for the above problem
Implementations solve this problem at the sender side by sending a
request for Route refresh (known as a bgp soft in request), after any
modification to vpn configuration. But, this is only a workaround.
The real problem is in the way bgp treats received RT. The
corrective measure should be at the receiver's side, by sending out
vpn routes in response, though the RT might be a duplicate. Further,
when the receiver has the ability to use RTs to walk only the
required VPN tables with an objective to avoid full walk, sending a
request for full route refresh will prevent the receiver from
utilizing its ability to walk required VPN tables for the RT. So,
sending a request for route refresh not only masks the problem in
2.1, but also leads to inefficient vpn walks at the sender capable of
selective vpn update generation per received RT.
5. Solution to the Problem
When the received RT is a duplicate, the receiver should respond with
vpn routes, rather than simply dropping the duplicate RT.
6. Acknowledgments
The author would like to thank P. Muthu and team for their
comments and review.
7. Security Considerations
There are no additional security considerations than the base BGP
RFC.
8. IANA Considerations
This document has no actions for IANA.
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9. Contributors
10. References
10.1. 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,
<http://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,
<http://www.rfc-editor.org/info/rfc4271>.
10.2. Informative References
[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, <http://www.rfc-editor.org/info/rfc4684>.
Author's Address
Anup Kumar T
Ericsson India Pvt Ltd
Ferns Icon, Doddanakkundi, Mahadevapura
Bengaluru 560037
India
Email: anupkumar.t@ericsson.com
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