"Tactical" /24 announcements

William Herrin bill at herrin.us
Thu Aug 12 17:19:44 UTC 2021

On Thu, Aug 12, 2021 at 9:41 AM Hank Nussbacher <hank at interall.co.il> wrote:
> 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

William Herrin
bill at herrin.us

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