"Tactical" /24 announcements

William Herrin bill at herrin.us
Thu Aug 12 17:29:08 UTC 2021

On Thu, Aug 12, 2021 at 10:19 AM William Herrin <bill at herrin.us> wrote:
> 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

I mashed this sentence together wrong. I meant say: "Unless A filters
packets from peers which would use their paid transit," a common
policy restriction placed on settlement-free peering.

> 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.

William Herrin
bill at herrin.us

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