[isp-bgp] Re: Outbound Balancing

[Pete Templin <petelists@...>]

Joe Pruett wrote:

> you can also use med values as a way to make selections. 
> after all those convolutions, i get decent traffic balancing for my 
> specific setup.  prefixes that match bgp-magic will look better for coming 
> in on l3.  for outgoing, the ones that match are slightly more likely to 
> go out l3 because of the extra path length on eli, but slightly better med 
> there.
Except that the MED simply doesn't matter on your router unless you're 
always comparing MED (which is not a default setting).

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.

To manage your outbound traffic:

1) Adjust weight if you have Cisco and you want to influence the 
decision on this one router only (caveat: this could change the "best 
path" selected on this router and therefore propagated to other routers 
if it's a border router).

2) Adjust local preference if you want to prefer a specific exit point 
essentially across your network.

3) Add prepends if you want to de-influence a specific exit point unless 
your preferred exit point(s) encounters a loss of connectivity in or 
beyond their network (which might result in the prepended path becoming 
best as a result of the outage).

4) Use MED to manage outbound traffic only if you have multiple pipes to 
the same upstream (the default scenario where MED even matters). 
Consider additive MED if your platform supports it and you can get a 
strong sense of the MED values from your upstream.

To manage your inbound traffic:

1) Add prepends if you want to de-influence a specific entrance point, 
while still allowing point outages (which probably result in a longer AS 
path) to trigger convergence away from the break point.

2) Attach communities to your routes based on your upstream policy to 
request specific values of local preference in their network and their 
upstreams' networks.

Pete






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