Re: [[e-mail]: Re: BGP4 stuff: Local Preference Computation]

[Curtis Villamizar <[e-mail]>]

In message <v03007823ae54d65762ae@[152.160.213.42]>2]>, "John G. Scudder" writes:
> At 2:55 PM -0400 9/5/96, Curtis Villamizar wrote:
> >The preconfigured policy information is then put into the LOCAL_PREF
> >attribute.  This text should be more clear.  It seems that everyone
> >who has already implemented BGP4 agrees on the interpretation but the
> >text was never very clear.
> >
> >Don't send LOCAL_PREF to an EBGP peer.  Don't accept LOCAL_PREF from
> >an EBGP peer.  Decide what your preference is based on configured
> >policy.  Then put that into LOCAL_PREF.  Then use LOCAL_PREF as the
> >first value in a comparison.
> 
> Speaking of things which aren't clear, the RFC (and draft) list LOCAL_PREF
> as a "discretionary" attribute.  It is of course *not* discretionary.  It's
> required on IBGP connections and forbidden on EBGP.  The implementor (or
> operator) has no discretion as to whether LOCAL_PREF is sent.
> 
> This should be fixed by reclassifying LOCAL_PREF as well-known mandatory.
> 
> [Other than the text being just plain wrong, the other possibility is that
> "discretionary" is being used to mean something like "this is only
> mandatory in some cases".  This is a terrible misuse of the language if
> true, and should still be fixed, if necessary by inventing some new term
> like "well-known sometimes-mandatory" or something.  (Note that the RFC
> nowhere defines "discretionary" so we are left with the dictionary
> definition, e.g. "left to discretion: exercised at one's own discretion".)]
> 
> --John


Let's just make it mandatory.  When is it not mandatory?  When there
is only one router in an AS?  Otherwise we have to define how you
compare no LOCAL_PREF to a route with LOCAL_PREF.

Curtis