Re: Addr: Re: BGP-4 - revised I-D

[Curtis Villamizar <[e-mail]>]

In message <[e-mail]>om>, Tony Li writes:
> 
>    I personally prefer NOT to compare MED values from different neighbor ASs.
>    The usage of MED is to distinguish multiple exit points to a particular
>    external AS.  If the WG decides to compare MED values from different ASs
>    then I suggest the definition of the MEDs and the reference to MEDs in
>    the bgp4 spec needs to be changed as well.
> 
> If one were to follow down this path of global MED values, we're pretty
> much all the way back to a global administratively defined metric.  We can
> go there if folks want, but global metrics have always been a rathole to be
> avoided.
> 
> I would further suggest that any such metric might as well be an entirely
> new attribute, and that we allow MED to die a quiet death.
> 
> Tony


Tony,

MEDs are useful and are still useful if compared across AS.  The way
we use BGP, no two AS should be announcing the same prefix at the same
local-pref under normal circumstances.  If the local-pref were the
same I'd rather have something that didn't form a routing loop.

I don't care if the solution is to compare MED across AS or to use
Rich Woundy's scheme of comparing allroutes on the basis of AS using
MED and then compare the best from each AS ignoring MED.  Both will
prevent route loops.  Some people find the former to be ugly but it is
much easier to code.

Getting rid of MED is not a constructive suggestion.

Curtis