BGP Confederation config problem...

Fri Mar 6 22:49:08 UTC 1998

More info:

Per Avi's suggestion, I implemented this route map for all outbound
advertisements:

	route-map addone permit 10
	  set metric +1

(assumes match all)

I'm running IOS 11.2 or 11.1(11) on the routers.  The Command reference
for 11.1 and 11.2 does not mention the ability to use +1 to increment, but
the online command "help" shows:

Enter configuration commands, one per line.  End with CNTL/Z.
router(config)#route-map addone
router(config-rou)#set metric ?
  +/-<metric>     Add or subtract metric
  <0-4294967295>  Metric value or IGRP bandwidth in Kbits per second
  <cr>

Does this really mean "Add one", or "Reset to Positive 1"?

-Andy

--
Andy McConnell       アンディ マッコネル
Network Architect, NTT Multimedia Communications Laboratories

Slogan of 105.9, the classic rock radio station in Chicago: "Of
all the radio stations in Chicago ... we're one of them."

On Fri, 6 Mar 1998, Andy McConnell wrote:

andym> I have a problem I cannot solve.  If anyone is running confederations like
andym> mine, I would appreciate some help :-)
andym> 
andym> We have a 4-memberAS confederation, each with two IBGP peers.  The
andym> arrangement looks sort of like an octagon.  the "r" is AS3 is an internal 
andym> hop, not a BGP peer.  
andym> 
andym>    _______     ______
andym>   |      R-----R---r |
andym>   |     / |   |    | |
andym>   |AS2 R  |   |AS3 R |
andym>    ----|--     ----|-
andym>        |           |
andym>    ____|__     ____|_
andym>   |AS4 R  |   |AS1 R |
andym>   |     \ |   |   /  |
andym>   |      R-------R   |
andym>    -------     ------
andym> 
andym> The problem is this:  How do you get BGP to choose the shortest "AS PATH",
andym> since internal AS paths are ignored in selecting BGP routes?  Right now,
andym> to top router in AS4 will always choose a route through (2 3 1) instead of
andym> (1), because it prefers "external" routes (even external confederation
andym> routes) over internal routes.
andym> 
andym> So, when given a choice, the router on the distant side of the AS will
andym> ALWAYS prefer the three-AS-hop path, because it is external.  Is there a
andym> way around this?!?
andym> 
andym> Avi Freedman suggested using a +1 metric when leaving each member-AS. 
andym> (Thanks Avi!) But it doesn't seem to help - perhaps I didn't do it right. 
andym> In fact, it doesn't look like the metrics are adjusted more than 1.  for
andym> example, from AS2, the lower router sees every route outside of AS2 as
andym> having only metric 1!  The top router in AS3 does not add 1 to the metrics
andym> it readvertises to AS2.
andym> 
andym> I've been stewing over this problem for some time... I believe there is
andym> some clue that I've missed.  Any help would be greatly appreciated!
andym> 
andym> -Andy
andym> 
andym> 
andym> --
andym> Andy McConnell       アンディ マッコネル
andym> Network Architect, NTT Multimedia Communications Laboratories
andym> 
andym> Writing about music is like dancing about architecture.
andym> 