Re: BCP38 - Internet Death Penalty

[William Herrin <bill () herrin us>]

On Thu, Mar 28, 2013 at 1:58 PM, Leo Bicknell <bicknell () ufp org> wrote:
> But the real power here comes by applying this filter further up the
> food chain.  Consider peering with a regional entity at an IX.  Most
> [...]
>
> That doesn't turn into a useful packet filter for the peer, but using my
> method the peer could be RPF filtered based on what they send,
> automatically.

Hi Leo,

Be nice if that were correct. If the best route you pick for the
customer's advertisement goes to your upstream instead of your
customer, you won't advertise it to your peer. And if your customer
sets a BGP community defined to mean "don't advertise to peers" then
you won't advertise it to the peer. Yet they may well transmit packets
to you for which delivery to that peer is directed by your routing
table.

Which means that your peer can't take the received routes from your
BGP session as gospel for what source addresses to expect.

Regards,
Bill Herrin




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William D. Herrin ................ herrin () dirtside com  bill () herrin us
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