Internet DRAFT - draft-francois-idr-addpath-limit
draft-francois-idr-addpath-limit
Network Working Group Pierre Francois
Internet-Draft Camilo Cardona
Expires: August 11, 2014 Institute IMDEA Networks
Adam Simpson
Alcatel-Lucent
Jeffrey Haas
Juniper Networks
February 7, 2014
ADD-PATH limit capability
draft-francois-idr-addpath-limit-00
Abstract
In this draft, we propose a new capability that allows BGP speakers
supporting ADD-PATH to announce a limit on the number of paths they
want to receive from their peers.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on August 11, 2014.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. The ADD-PATH Limit capability . . . . . . . . . . . . . . . . . 3
3. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 5
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1. Introduction
ADD-PATH is an extension to BGP that allows a BGP speaker to send and
receive more than one path for the same NLRI [AddPath]. The ADD-PATH
capability does not include any mechanism for restricting the number
or type of paths that a peer can receive from others. Thus, a
receiving BGP speaker has no control on the number of paths sent by
its peer, which depends only on the mode the operator desires to
implement in the transmitting side [AddPathGuidelines]. This
restriction can make network operations more difficult in some
situations:
o In cases in which all network devices are managed by the same
group, operators select the ADD-PATH mode that best fits the
resources of each of their devices. Operators must configure
manually each speaker with a mode that does not overload the
resources of the other devices. The overhead of this procedure
can be high in some networks, as this configuration must be
performed at the session level. If a ADD-PATH router could signal
a limit in the number of paths it wants to receive, operators
could achieve the same resource control by performing a more
simple configuration.
o In cases in which devices are managed by different operators, such
as in networks spanning large geographical regions or in Internet
Exchange Points, operators must agree on the ADD-PATH mode to use
between BGP speakers. If one of the devices has constraints on
the number of paths it can receive, the other party must configure
an ADD-PATH mode that does not overload the memory of other
device. Under these circumstances, allowing the receiving side to
limit the number of paths can ease the management process for all
administration sides.
In this document, we propose a new capability that allows an ADD-PATH
capable BGP speaker to set an explicit upperbound on the number of
paths it wants to receive from its peer.
2. The ADD-PATH Limit capability
+------------------------------------------------+
| Address Family Identifier (2 octets) |
+------------------------------------------------+
| Subsequent Address Family Identifier (1 octet) |
+------------------------------------------------+
| Flags(1 octet) |
+------------------------------------------------+
| Receive bound (2 octet) |
+------------------------------------------------+
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Figure 1: Capability
The meaning and use of the fields are as follows:
Address Family Identifier (AFI):
This field is the same as the one used in [RFC4760].
Subsequent Address Family Identifier (SAFI):
This field is the same as the one used in [RFC4760].
Flag Field
This field contains different bit flags related to the ADD-PATH
limitation capability.
The most significant bit of the field (limit-capable bit) is
used to communicate if the device supports the limitation of
paths announced to the peer. If the router supports the ADD-
PATH Limit capability, but it is not capable of limiting the
number of announced paths, it should set the limit-capable bit
to 0.
The remaining bits MUST be set to 0 and SHOULD be ignored upon
receipt.
Receive Bound
This field indicates the maximum number of paths the device
wants to receive from a peer for the <AFI, SAFI>. If the field
is set to 0, the device has no restriction on the number of
paths it can receive.
3. Operation
The ADD-PATH Limit capability SHOULD be announced by BGP speakers
that require their neighbors to send a limited number of paths per
prefix. A router that is capable of sending a limited number of
paths to a BGP ADD-PATH neighbor SHOULD also announce the ADD-PATH
Limit capability. For cases in which a router is not capable of
setting a limit in the number of paths it sends to a peer, it should
set the limit-capable bit in the add-path capability to 0.
The ADD-PATH capability is a prerequisite of the ADD-PATH Limit. A
BGP peer SHOULD ignore the ADD-PATH Limit capability from a peer that
did not also announce the ADD-PATH capability.
The ADD-PATH limit capability is used to set an upper bound on the
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number of paths that the router wants to receives from a peer. A
sender capable of limiting the number of paths per peer SHOULD NOT
send more paths than requested by the receiver.
It might be impractical for a BGP speaker to strictly stick to each
of the upper bounds specified by its peers. Thus, the sender MAY
send a lower amount of paths than the upper bound indicated by its
peer.
A router SHOULD include the best path in the subset of paths to send
to a peer, except when the best path is received from that peer. The
choice of the rest of paths to be sent is left free to the
implementation.
A BGP speaker could receive more paths than the number defined in the
ADD-PATH capability, even when the BGP peer supports the limitation
of paths. This event should be logged, but the session with the peer
should be preserved. The receiving speaker should implement the
required mechanism to deal with more paths that it can support.
4. References
[AddPath] D. Walton, E. Chen, A. Retana, and J. Scudder,
"Advertisement of Multiple Paths in BGP",
draft-ietf-idr-add-paths-09.txt (work in progress).
[AddPathGuidelines]
J. Uttaro, P. Francois, R. Fragassi, A. Simpson, and K.
Patel, "Best Practices for Advertisement of Multiple Paths
in IBGP", draft-ietf-idr-add-paths-guidelines-05.txt (work
in progress).
Authors' Addresses
Pierre Francois
Institute IMDEA Networks
Avda. del Mar Mediterraneo, 22
Leganes 28918
ES
Email: pierre.francois@imdea.org
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Camilo Cardona
Institute IMDEA Networks
Avda. del Mar Mediterraneo, 22
Leganes 28918
ES
Email: juancamilo.cardona@imdea.org
Adam Simpson
Alcatel-Lucent
600 March Road
Ontario K2K 2E6
CA
Email: adam.simpson@alcatel-lucent.com
Jeffrey Haas
Juniper Networks
1194 N. Mathilda Ave
Sunnyvale 94089
USA
Email: jhaas@juniper.net
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