nested prefixes in Internet

Victor Sudakov vas at
Mon Nov 21 14:08:07 UTC 2016

Niels Bakker wrote:
> >I have reports that in case (2), some operators (e.g. Rostelecom) 
> >don't accept the /24 or even /23 prefix on the grounds that it is 
> >part of a larger /19 route already present in the routing table.
> >
> >Could they have a reason not to accept these more specific prefixes 
> >other than a whim?
> If you announce a prefix you must deliver traffic sent to addresses 
> covered by it.  You don't go announcing to your peers either.
> If a customer takes a /24 and announces it elsewhere, a transit 
> provider runs the risk of accepting inbound traffic without having 
> the possibility to bill their customer for it if it accepts more 
> specifics from e.g. a peer.

That's all correct from the point of view of the provider annoncing
the /19 route, and should be their risk.

My question was however from a different perspective. If AS333
receives a /19 from AS111 and a /24 from AS222 (where AS222's /24 is
nested within AS111's /19), what reason might AS333 have to ignore the /24? 
AS333 is not concerned with possible monetary relations between AS111
and AS222.

Victor Sudakov,  VAS4-RIPE, VAS47-RIPN
sip:sudakov at

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