[isp-bgp] Re: Outbound Balancing

[Iljitsch van Beijnum <iljitsch@...>]

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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