[ppml] Technical reason why /52,/56,/60,/64 are bad

Scott Leibrand sleibrand at internap.com
Sun Aug 19 21:48:51 EDT 2007

The Assignment Guidelines proposal attempts to dictate what size 
prefixes LIRs (ISPs) assign to their customers.  Such space, assigned by 
a provider, is PA (provider assigned).  PI space is Provider 
Independent, meaning it is assigned directly by ARIN or other RIRs to 
end sites.  PI space is not affected by this policy proposal.

It is unclear to me whether this proposal would result in prefixes 
longer than /48 appearing in BGP.  I suspect that what would happen 
instead is that anyone wanting to run BGP using PA space would still get 
a /48 (as they get /24's today) whether they expect to fully utilize it 
or not, and that smaller prefixes would be reserved for customers not 
running BGP.

Regardless of whether there would be an impact to the DFZ, I remain 
opposed to the Assignment Guidelines proposal, as I believe that the 
existing guidelines (with two sizes, /48 and /56) are more appropriate, 
and that this is a matter best left to ISPs, with only general 
guidelines as to what to assign to whom.


Robin Whittle wrote:
> Michael Dillon quoted something I wrote on the IETF list, in
> response to the PPML message:
>    http://lists.arin.net/pipermail/ppml/2007-August/008521.html
> It was my initial impression that these longer prefixes, to /64,
> were being assigned (allocated? - I get confused with the
> terminology) by RIRs as PA space for end-users.  That would mean
> that there would be BGP advertised prefixes of this length, with the
> consequent need for all BGP routers to process 64 bits of
> destination address of some packets in their FIBs.
> After I wrote my first message, which Michael quoted, I read the
> PPML message more carefully and saw that it concerned LIRs
> (effectively ISPs, I think) providing PI space for their customers.
>  This would mean that the /64 prefixes would not be advertised in
> BGP.  So I wrote a retraction to the IETF list:
>   http://www1.ietf.org/mail-archive/web/ietf/current/msg47249.html
> Can someone confirm my second understanding is correct?
>  - Robin
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