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Re: /24's run amuck?

  • From: Josh Richards
  • Date: Wed Feb 14 16:44:32 2001

* Valdis.Kletnieks@vt.edu <Valdis.Kletnieks@vt.edu> [20010206 21:02]:
> 
> So - who wants to crunch the numbers and figure out how many
> of those 58K are useless punchouts ("Route all of 128.257.x.x
> to me, except for 128.257.219.x, which also goes to me")....

Uhm, except that many punchouts are done so that someone else can 
*originate* announcements for that block and control their own metrics.  
Likely the ASN announcing 128.257.x.x is one of those still transitting 
traffic for that punched out network, but they no longer are the origin for
the more specific announcement.  In this way, the utilizer of the more 
specific can do things like prepending or whatever they like.  It is fairly
common when someone multihomes with non-ARIN space.  If they pull IP space
from one of their upstreams, they need to be able to announce equally 
specific /x routes via both or suffer funky inbound traffic patterns.  This
isn't possible if the upstream the space is from doesn't do the punchout 
for them. Considering how many multihomed sites there are without 
justification for a </19 (or /20) how else do you suppose they gain control
over their announcements?

So a more accurate way to figure out how many of those 58K are useless 
punchouts would be to first ask for the ones that say "Route all of 
128.257.x.x to me, except for 128.257.219.x, which also goes to me" then
to see if 128.257.219.x is also being announced via any other transit 
providers.

Unless I'm misreading the punchouts you are referring to.

Additionally, it remains impossible to *truly* know the intent of someones
routing policy without asking them.  I mean, some people could have funky
routing backup scenarios that routing announcements that look odd to all of
us looking into their network.  I'm not saying they are right or they are
wrong -- I'm saying it is difficult to tell unless you understand the
reason behind every single ASNs announcement choices.  Granted, some ASNs
have no idea themselves.  But how can you tell the difference between those
ones and the ones with legit reasons?  

Nonetheless, none of these reasons are excuses to announce useless stuff 
that could be aggregated beyond your ASN.

We need to continue work on infinite IP space and a scalable inter-AS
routing protocol to match.  That way, as long as you aren't announcing
any networks that aren't yours, I don't care how mangled your 
announcements are to me. :-)

-jr

----
Josh Richards [JTR38/JR539-ARIN]
<jrichard@geekresearch.com/cubicle.net/fix.net/freedom.gen.ca.us>
Geek Research LLC - <URL:http://www.geekresearch.com/>
IP Network Engineering and Consulting





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