Re: "Tactical" /24 announcements

[William Herrin <bill () herrin us>]

On Thu, Aug 12, 2021 at 10:39 AM Amir Herzberg <amir.lists () gmail com> wrote:
> On Thu, Aug 12, 2021 at 1:22 PM William Herrin <bill () herrin us> wrote:
> > A originates 10.0.0.0/16 to paid transit C
> > B originates 10.0.1.0/24 also to paid transit C

> Bill, I beg to respectfully differ, knowing that I'm just a researcher and working `for real' like you guys, so pls 
> take no offence.

Hi Amir,

Why would I take offense? How do any of us learn except by trying to
poke holes in claims to see what holds up and what doesn't?


> I don't think A would be right to filter these packets to 10.0.1.0/24; A has announced 10.0.0.0/16 so should route to 
> that (entire) prefix, or A is misleading its peers.

The alternative is that A has to disaggregate 10.0.0.0/16 into at
least 8 prefixes on the -possibility- that some jackass might filter
the one /24 that B announces. If trying to filter one route results in
7 extra routes being added to the table, that's net badness.

Filtering may not even be intentional on A's part. If A's peering
router only receives A's customer-originated routes (a common enough
architecture) then the peering router won't even have a route to B
while B's route only arrives from C.

Regards,
Bill Herrin


-- 
William Herrin
bill () herrin us
https://bill.herrin.us/