meeting
Joe Abley
jabley at nlri.org
Thu Nov 22 18:04:43 UTC 2001
On Thu, Nov 22, 2001 at 04:46:43AM -0800, Randy Bush wrote:
> > Following on from the August WG meeting, I would like to pass
> > draft-huston-nopeer-00.txt to the WG to be adopted as a WG item.
>
> this initiates a two week wg call on whether this work should become
> draft-ietf-ptomaine-nopeer-...
>
> > Does it need consideration in the WG meeting?
>
> i think the technical details are worth some back and forth. there are
> subtle alternative semantics, yes?
>
> so, so far, our agenda would be
> o agenda bashing
> o discussion of draft-huston-nopeer-00.txt
> o administrivia
> - [how] do we proceed?
> - any charter changes?
> - new chair
>
> more documents needed!
I circulated draft-jabley-edge-policy-propagation-control-01 during
Minneapolis, but there wasn't much discussion, I got distracted, and
it didn't get sent to internet-drafts.
Ben Black and I wrote most of a similar draft, providing the same
propagation control mechanisms using new proposed BGP attributes
(in the context of which draft-jabley was a proof-of-concept using
community strings).
My draft draft can be found at:
http://buffoon.automagic.org/dist/draft-jabley-edge-policy-propagation-control-02.txt
and is attached below.
Joe
-------------- next part --------------
Network Working Group J. Abley
Internet-Draft MFN, Inc.
Expires: May 23, 2002 November 22, 2001
Edge Policy Propagation Control
draft-jabley-edge-policy-propagation-control-02
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
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The list of current Internet-Drafts can be accessed at
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The list of Internet-Draft Shadow Directories can be accessed at
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This Internet-Draft will expire on May 23, 2002.
Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract
There is a requirement for some multi-homed sites to influence the
path selected by autonomous systems beyond those that are immediately
adjacent.
This draft describes a community-based convention which might be used
to limit propagation of particular prefixes to those ASes where they
are required.
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1. Introduction
There is a requirement for some multi-homed sites to influence the
path selected by autonomous systems beyond those that are immediately
adjacent.
One of the few generic mechanisms available is to deaggregate and
advertise long component prefixes to the network, since there can be
some confidence that the longest prefix will be used, regardless of
other local policy such as local preference. Most ASes exhibit
liberal route import policy with respect to prefix length, which
facilitates this technique.
Unfortunately, although the deaggregated prefix set may be required
to be installed in only a few targeted ASes for the aims of the
origin to be achieved, there is no reliable mechanism to limit the
propagation of the prefixes. This contributes to prefix bloat in the
default-free zone, which is a concern.
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2. Terminology
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 [1].
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3. Edge Policy Propagation Convention
3.1 At the Edge
An edge site deaggregates its advertisements according to the
required fine-grain policy. Aggregate prefixes are advertised as
normal; long prefixes are advertised tagged with community attributes
which define their scope:
EPPC_ALLOW:0 -- this prefix should be handled according to the
convention described in this document.
EPPC_ALLOW:A -- it is desirable that this prefix should propagate to
AS A. Multiple communities of the form EPPC_ALLOW:A may be
present to define propagation scope.
EPPC_ALLOW is some 16-bit quantity, well-known amongst the community
of operators who cooperate according to this convention. It should
be chosen from the private-use range of ASNs specified in [2].
3.2 Towards the Other Edge
ASes which support this convention MUST include additional clauses in
their advertisement policy to all neighbour ASes, as follows.
3.2.1 Egress Policy
When announcing prefixes to AS A:
o if the community attributes EPPC_ALLOW:0 and EPPC_ALLOW:A are both
present, then the announcing router MAY advertise the prefix.
o If the community attribute EPPC_ALLOW:0 is present, and
EPPC_ALLOW:A is not present, then the announcing router MUST
suppress the advertisement.
3.2.2 Ingress Policy
When AS B receives announcements from any other AS:
o if the community attribute EPPC_ALLOW:B is present, the receiving
router MUST drop the advertisement.
An implementation of this policy for cisco and Juniper routers can be
found in Section 5.
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3.3 Related Work
A similar approach based on a new BGP attribute is described in the
companion document draft-black-prop-path-00.txt.
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4. Example
Consider the following internetwork:
+------+
+-----+ AS B +-----+
| +---+--+ |
+---+--+ | +--+---+ +------+
| AS A | | | AS D +----+ AS F |
+---+--+ | +--+---+ +------+
| +---+--+ |
+-----+ AS C +-----+
+---+--+
|
+---+--+
| AS E |
+------+
AS A requires a particular set of prefixes to propagate within AS B,
D and F, but not elsewhere.
AS A therefore advertises the set of prefixes with the community
attributes EPPC_ALLOW:0, EPPC_ALLOW:D and EPPC_ALLOW:F.
AS B suppresses the advertisements towards AS C, since the community
attribute APPC_ALLOW:0 is present without APPC_ALLOW:C. AS B
advertises the prefixes towards AS D.
Similarly, AS D suppresses the advertisements towards AS C, and
advertises the prefixes towards AS F.
AS F suppresses the advertisements towards all peers, since
APPC_ALLOW:0 is present without any other matching APPC_ALLOW:*
community.
The result is that the long prefix routes only propagate to AS B, AS
D and AS F, in accordance with the policy specified by AS A.
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5. Sample Implementations
5.1 Juniper JUNOS
policy-options {
/* EPPC policy towards A. */
policy-statement eppc-to-A {
/* If this route is an EPPC route and is for A, then delete
* EPCC:A and continue.
*/
term is-A {
from community [ comm-eppc-zero comm-eppc-A ];
then {
next policy;
}
}
/* If this route is an EPPC route, then drop it. */
term is-eppc {
from community comm-eppc-zero;
then reject;
}
/* Otherwise continue as normal. */
then next policy
}
/* The EPPC:0 community */
community comm-eppc-zero members EPPC_ALLOW:0;
/* The EPPC:A community meaning send to AS A */
community comm-eppc-A members EPPC_ALLOW:A;
}
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5.2 cisco IOS
ip community-list EPPC-0 permit EPPC_ALLOW:0
ip community-list EPPC-200 permit EPPC_ALLOW:200
!
route-map AS200 permit 10
match comm-list EPPC-0 EPPC-200
!
route-map AS200 deny 20
match comm-list EPPC-0
!
route-map AS200 permit 30
!
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6. Acknowledgements
Thanks to Andrew Partan for excellent envelope-scribbling and for the
Juniper config fragment.
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References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, March 1997.
[2] Hawkinson, J. and T. Bates, "Guidelines for creation, selection,
and registration of an Autonomous System (AS)", RFC 1930, March
1996.
[3] Huston, G., "Analyzing the Internet's BGP Routing Table",
January 2001.
Author's Address
Joe Abley
MFN, Inc.
10805 Old River Road
Komoka, ON N0L 1R0
Canada
Phone: +1 519 641 4368
EMail: jabley at mfnx.net
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Abley Expires May 23, 2002 [Page 11]
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