"Tactical" /24 announcements

Jason Pope boards188 at gmail.com
Mon Aug 16 14:09:55 UTC 2021

>On Thu, Aug 12, 2021 at 9:41 AM Hank Nussbacher <hank at interall.co.il>
>> On 12/08/2021 17:59, William Herrin wrote:
>> > If you prune the routes from the Routing Information Base instead, for
>> > any widely accepted size (i.e. /24 or shorter netmask) you break the
>> > Internet.
>> How does this break the Internet?  I would think it would just result in
>> sub-optimal routing (provided there is a covering larger prefix) but
>> everything should continue to work.  Clue me in, please.
>A originates to paid transit C
>B originates also to paid transit C
>C offers both routes to D. D discards from the RIB based
>on same-next-hop
>You peer with A and D. You receive only since A doesn't
>originate and D has discarded it.
>You send packets for to A (the shortest path for
>, stealing A's paid transit to C to get to B.
>Unless A filters C-bound packets purportedly from B
>doesn't currently transit for A so from B's perspective that's not an
>allowed path. In which case, your path to is black holed.
>D broke the Internet. If packets from you reach A at all, they do so
>through an unpermitted path.
>Bill Herrin

Ok, I apologize, but I have some dumb questions (because I don't BGP

1) I assume in the scenario that A "owns" (ARIN assignment) and
if B has a /24 assignment out of the block that A "owns", shouldn't that
mean that B has a business relationship with A and some kind of direct
connectivity to A?

2) If "no", then why is B using a /24 out of A's block? If A sold or gave
the block to B without a connectivity agreement, then A should break up
their announcements appropriately to carve the /24 out of their
announcement, right?

3) If "yes", then the connectivity wouldn't be broken, right?

TIA for the tutoring and bearing with me.

Jason K Pope
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