[ppml] alternative realities (was PIv6 for legacy holders (/wRSA + efficient use))

Scott Leibrand sleibrand at internap.com
Thu Aug 2 13:57:59 EDT 2007

Peter Eisch wrote:
> ...or you'll be black-holed if your Cogent line is down while your other
> ISP's circuit is alive and kicking.

Not if Cogent accepts your /24 from your other ISP.  And if you pay them 
to, I'm sure they will.

> Multi-homing in that reality becomes hit and miss.  It's not worth paying
> any fees to the second ISP if anyone who wants to reach you is sitting
> behind a filtering ISP.  The funny part is that they lose you as a customer
> based on policy enacted by a non-related entity.

Yes, I realize that multihoming is "easier" and "better" without 
filtering, which is why no one filters any longer.  However, I did 
troubleshoot the problems that occurred back when Verio filtered, and 
while it's better to no longer have to do so, it wasn't an 
insurmountable problem to deal with, either.

Going forward, I don't think tier 1 NSPs are going to choose to filter 
each other's routes aggressively, unless the deaggregation gets really 
bad.  However, I do think that a large spike in deaggregation due to 
IPv4 free pool exhaustion will prompt a new look at route filtering 
policies.  I suspect a number of networks will discover they can safely 
filter distant deaggregates, and tools like as-pathlimit will be 
deployed to assist in this.  We may even see router vendors deploying 
BGP stacks that can automatically filter out unnecessary deaggregates 
(such as those whose next-hop is identical to a covering BGP route, and 
whose local-pref is equal or lower and as-path is equal or longer).  I 
wouldn't advocate turning on such features toward your customers, but I 
could definitely see people deploying it on routes received from their 
transit providers.

Whatever alternate reality we end up with, I think we can trust network 
operators to do what's in their best interest, and to find a way to 
effectively deal with IPv4 deaggregation, as long as we don't completely 
abandon aggregation and hierarchical allocation.


> On 8/2/07 11:06 AM, "Scott Leibrand" <sleibrand at internap.com> wrote:
>> Steven,
>> Does Cogent have a route to your /24?  Do they announce a covering
>> aggregate?  If so, then you will retain reachability even to networks
>> who filter your /24, via Cogent's aggregate..
>> -Scott
>> Steven E. Petty wrote:
>>>    I'm not certain your assumptions are valid.  I know my workplace is
>>> currently multihomed using a /24 assigned from cogent in the 38.  This
>>> filter would remove my routes.  Under current ARIN policies, our two
>>> dozen or so hosts don't qualify us for a direct assignment/allocation
>>> despite multi-homing.
>>>    Steve

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