Thus spake Zhang, Ou (David) (OuDavid.Zhang@gs.com):
> Can someone name the pros and cons of using local preference and MED
> ?
It depends what you want to achieve.
> For instance, one problem of using local preference is that it
> overwrites as-path.
This is exactly why you would use it in certain situations. For
example if sending traffic via one BGP peer costs you money and the
other doesn't you might want to send traffic via the cheap one even if
it's via a longer as-path. You could use a local-pref to achieve this
as local-pref is checked before as-path.
> The problem of using MED is that you have to rely on other
> organizations. Thanks.
You don't have to rely on other organisations. You can use a route-map
to set the MED on incoming advertisments to anything you wish,
overwriting whatever the other organisation sets. [Hello Level3!]
Alternatively, rather than overwriting the MED on your incoming
announcements you can use a route-map to manipulate it higher or
lower, for example adding 100 to some advertisments and 50 to others.
Your peers can still influence your routing decision especially if you
tell them what your policy is but so can you.
Remember that depending on what you do you might want to set bgp
always-compare-med and almost certainly bgp deterministic-med.
So both local-prefs and MED's are useful in different situations. It
depends what you want to do.
Mark
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