an effect of ignoring BCP38

Kevin Oberman oberman at
Thu Sep 11 13:24:43 CDT 2008

> Date: Thu, 11 Sep 2008 20:59:39 +0300 (EEST)
> From: Pekka Savola <pekkas at>
> On Thu, 11 Sep 2008, Jo Rhett wrote:
> > On Sep 11, 2008, at 10:10 AM, Valdis.Kletnieks at wrote:
> >> By the time you walk our list of upstreams to any of the '5 biggest 
> >> anything', you've gotten to places where our multihomed status 
> >> means you can't filter our source address very easily (or more 
> >> properly, where you can't filter multihomed sources in general).
> >
> > I don't agree with this statement.  I hear this a lot, and it's not really 
> > true.  Being multihomed doesn't mean that your source addresses are likely to 
> > be random.  (or would be valid if they were)
> >
> > A significant portion of our customers, and *all* of the biggest paying ones, 
> > are multihomed.  And they might have a lot of different ranges, but we know 
> > what the ranges are and filter on those.
> If you can manage ACLs for these customers, that's fine.  But maybe 
> your multihomed customers and '5 biggest anything' customers are 
> different.  Maybe your multihomed customer has 5 prefixes.  The big 
> ones could have 5000.  That's a pretty big ACL to manage.

It's big, but not un-workable. Just looking at our lists, the longest is
over 212K entries and we have 5 over 5K and 20 over 1K. We would have
even bigger ones if the IRR had more complete information.

I'll admit that doing this for a tier-1 would probably not work, though
I have never been able to try as the requisite information is not
publicly available.
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at			Phone: +1 510 486-8634
Key fingerprint:059B 2DDF 031C 9BA3 14A4  EADA 927D EBB3 987B 3751
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