BGP multihoming with two address spaces

Michael Hallgren m.hallgren at
Wed Jan 29 20:24:26 UTC 2014

Le 29/01/2014 20:34, Owen DeLong a écrit :
>> This sort of local-pref default seems to be a common practice with
>> backbones. It's very annoying. I wish they'd stop.
> Most of their customers would actually be very unhappy if they stopped. This local-pref default prevents many many problems and in the vast majority of cases provides the desired result. Yes, it's important to know what is going on and to be able to ask your providers to make necessary changes in circumstances where this is not optimal (either via community or ticket), but I assure you that if every backbone turned this off suddenly, most internet users would be very !HAPPY.

The underlying reason for this type of local preference has to do with
an assumption of cost
(which, given current transit prices, may be true or not):

        cost(customer) < 0 < cost(peer) < cost(provider) ..., thus

        local_pref(customer) > local_pref(peer) > local_pref(provider),

and as you say Owen, many actors sharing a policy simplifies our view of
things a bit. Another
way of assigning local preference of a route may factor in measured or
perceived path quality,
slightly more complex, but not a crime at all :-).


> Owen

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