[arin-ppml] Rationale for /22

Scott Leibrand scottleibrand at gmail.com
Tue Jul 28 13:50:25 EDT 2009

Kevin Kargel wrote:
>> AFAIK, there are no ISPs allowing customers to multihome with less
>> than a /24 currently but many who are allowing those /24s.  So if that
>> Org gets a /24 from ARIN or a /24 from it's ISP, there is the same 1
>> entry in the table.  
> This is incorrect.  If the Org gets a /24 from it's upstream ISP there is
> the same entry in the routing table.  If the Org gets a discontiguous /24
> from ARIN there is an additional entry in the routing table.  
> What it boils down to is whether or not the Org's ISP can aggregate the
> netblock.

No, we're talking about multihomed organizations here.  If my 
singly-homed customer gets a /24 from me (out of one of my /16s), then 
that doesn't add to the table (the only announcement is my /16).  If, 
however, a multihomed customer gets a /24 from me, they'll announce the 
/24 as well (both to me and to their other upstream), thereby adding an 
additional route to the global table (for anyone who doesn't filter 
/24s, which very few networks do today).

If the multihomed downstream customer gets their /24 from ARIN instead 
of from me (their upstream), then it still adds one route to the table.  
The only difference is that it can't be filtered without affecting 
reachability (for example, by someone with hardware that can only do 
256k routes).


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