Re: Upstreams blocking /24s? (was Re: How Not to Multihome)

[Vince <jhary () unsane co uk>]

Scott Weeks wrote:
> --- drc () virtualized org wrote:
> On Oct 8, 2007, at 2:48 PM, Scott Weeks wrote:
>
> > However, if it's less than a /24 it won't get very far as most  
> > upstreams block prefixes longer than a /24.
>
> I'm curious: a couple of people have indicated they do not believe  
> this to be the case. Anybody have any hard data on what filters are  
> actually in use today?
> --------------------------------------------
>
>
> I found two current policies.  Other companies made it too hard to find...
>
>
> Sprint:
> #  Customers may announce routes as small as /26 for ARIN IP address blocks obtained through Sprint. Customers may 
> announce routes as small as /28 for RIPE and APNIC address blocks obtained through Sprint. 
>
> # Peer block announcements and customer announcements for blocks obtained from other providers are limited to a /24 
> or smaller mask (/23, /22 etc.).
>
>
>
> AT&T:
> * not accept Customer route announcements smaller than a /24 network
Level3:
> From the output of
whois -h rr.level3.net AS3356
<snip>
remarks:       The following import actions are common to every
remarks:       Level 3 non-customer peering session:
remarks:
remarks:       - RFC1918 and other reserved networks and subnets are
remarks:       not permitted.
remarks:
remarks:       - Advertisements with reserved ASes in the path
remarks:       (ie 64512 - 65535) are not permitted.
remarks:
remarks:       - Prefixes shorter than /8 or longer than /24 are
remarks:       not permitted.
<snip>

(the rest is useful reading too if you deal with level3 much)

Vince


> scott