[isp-bgp] Re: Outbound Balancing

[James <haesu@...>]

okay, using med to control your outbound routing policy is pretty
stupid when you can still get around with other attributes.

the purpose of The MED is to have a view into your direct neighbor's
topology. of course when MED starts traversing multiple ASN's, it
becomes pretty damned useless (hence why transitive MED is pretty
bad idea).

just set a higher local-pref value on the destination routes you
care about. i just can't see why people need 3 knobs to control
egress traffic. you get two: local preference and IGP cost. then
again, many of you are already probably breaking next-hop's for IGP
cost to be useful, so then you are left out with just _one_. what
a shame eh?


-J

On Thu, Apr 29, 2004 at 09:28:34AM +0200, Iljitsch van Beijnum wrote:
> On 28-apr-04, at 16:39, Pete Templin wrote:
> 
> >>>Folks, use the tools in the manner that they're suggested, rather
> >>>than a convoluted way, since there's obviously a wide selection of
> >>>tools in the tool kit.
> 
> >>Suggested by whom? If there is a single authority on BGP traffic
> >>engineering that fact has managed to escape me over the past years.
> 
> >Suggested by the mere nature of the propagation of the attributes.  In
> >other words, why use an attribute that propagates to the next adjacent
> >AS for intra-AS tuning?
> 
> When you set the MED with a route map applied for inbound, the MEDs you
> see in your BGP table aren't propagated to external ASes (at least not
> on a Cisco box).
> 
> >How can you say MEDs are orthogonal to local preference when you said
> >MED only matters if local preference matches on two path choices?
> 
> What I mean is that I can set both a MED and a local preference
> independently, and each will do what I want it to do. For instance, I
> can set a higher local preference for routes received from peers, and
> this leaves the MED as a tie breaker for routes that are both from
> peers or that are both not from peers.
> 
> >Better to use the same matching algorithms (if AS path = 12345 1234)
> >and twiddle local preference, since "always compare MED" will become a
> >disaster if there's ever a second link to the same network added.
> 
> What's the disaster that happens in this case?
> 
> 
> 




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-- 
James Jun                                            TowardEX Technologies, Inc.
Technical Lead                        Network Design, Consulting, IT Outsourcing
james@...                  Boston-based Colocation & Bandwidth Services
cell: 1(978)-394-2867           web: http://www.towardex.com , noc: www.twdx.net






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