Re: IDR WG agenda
Curtis Villamizar <curtis@ans.net> Sat, 01 March 1997 00:05 UTC
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To: Paul Knight <pknight@baynetworks.com>
Cc: bgp@ans.net
Reply-To: curtis@ans.net
Subject: Re: IDR WG agenda
In-Reply-To: Your message of "Thu, 27 Feb 1997 16:23:37 EST." <3315FB59.6FBE62C0@BayNetworks.com>
Date: Fri, 28 Feb 1997 10:25:56 -0500
From: Curtis Villamizar <curtis@ans.net>
Sender: owner-idr@merit.edu
Precedence: bulk
In message <3315FB59.6FBE62C0@BayNetworks.com>, Paul Knight writes: > I believe Curtis is right about this. > > There is clearly a well-known community (NO_ADVERTISE) which looks like > it should accomplish this (allowing setting a local-pref known only at a > specific router). > > from draft-ietf-idr-communities-00.txt: > > Well-known Communities > > The following communities have global significance and their > operations shall be implemented in any community-attribute-aware BGP > speaker. > NO_EXPORT (0xFFFFFF01) > All routes received carrying a communities attribute containing > this value MUST NOT be advertised outside a BGP confederation > boundary (a stand-alone autonomous system that is not part of a > confederation should be considered a confederation itself). > NO_ADVERTISE (0xFFFFFF02) > All routes received carrying a communities attribute containing > this value MUST NOT be advertised to other BGP peers. > NO_EXPORT_SUBCONFED (0xFFFFFF03) > All routes received carrying a communities attribute containing > this value MUST NOT be advertised to external BGP peers (this > includes peers in other members autonomous systems inside a BGP > confederation). That's not quite it. NO_ADVERTISE works if you are sending a more specific route that you want propogated no further than the immediate router. There are some cases. Most are covered. 1. You want to provide a MED solely for the purpose of choosing one of two routers. You want the prefixe advertised into the entire world after the choice is made. This (I think) is Vince's case and it is not covered. Nothing a new community wouldn't fix. 2. You want to provide a MED for the purpose of selecting an exit point among many interconnect points. This is covered. Just send MED (the other end may refuse it, opting for shortest out). 3. You would like to send one metric to pick an interconnect and another to select the next hop at the preferred interconnect. This could be done with MED. Multiple all link metrics by N (reconfigure your IGP, if you don't have some sort of MED algebra on your router, none do). Then add a small offset (less than N) to choose among as many as N routers. 4. You either have 1 router, or more than 1 routers and 0 clues, or your routers are broken or have no practical way to configure MED and/or communities, or you are paranoid that someone else's router is broken or you don't care where traffic goes. Don't send MED and/or communities. 5. You want to send more specifics to refine the next hop at the immediate router. Set MED and NO_ADVERTISE on the more specifics. 6. You want to send send more specifics to refine the exit point among multiple interconnects. Set MED and NO_EXPORT on the more specifics. 7. You have intimate knowledge of your peer's topology and want to send more specifics to choose among multiple interconnects that you know are within the same BGP confederation in your peer's topology. Set MED and NO_EXPORT_SUBCONFED (consenting adults only). 8. You just heard about BGP and don't really understand much of this aggregation, loca-pref, MED, community, confederation, stuff. You want to advertise everything you know to your peer and hope they can figure out the right thing to do with it and you can't be bothered registering any information about your AS or prefixes. Leave the planet. :) Did I miss any cases? (Actually I might have one or two extras). Curtis - - - - - - - - - - - - - - - - -
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