Aggregation & path information [was: 200K prefixes - Weekly Routing Table Report]

Jared Mauch jared at
Fri Oct 13 19:26:35 UTC 2006

On Fri, Oct 13, 2006 at 03:14:38PM -0400, Patrick W. Gilmore wrote:
> On Oct 13, 2006, at 3:04 PM, Philip Smith wrote:
> >I was kinda hoping that it would hit 200K on Tuesday, then I could  
> >have
> >added the announcement to my aggregation recommendations lightning  
> >talk!
> >;-) Bit sad that a 200K table can be aggregated down to 109k prefixes
> >with no loss of path information (in my BGP table view).
> I find this interesting.
> Obviously the table contains kruft.  But I know we could not shrink  
> it to 109K prefixes without losing something from where I sit.  Are  
> you sure there's no additional path info?
> If there were a way to guarantee certain prefixes are completely  
> superfluous, we could make a hit list of just those providers, then  
> ridicule or filter or cause them pain in some way to make them stop  
> causing us pain.  I haven't seen that type of report posted publicly,  
> just "this CIDR can fit in that one" without actual guarantees that  
> _paths_ are equivalent.  (Usually the origin AS is matched as well as  
> the prefixes, but that's not the same as guaranteeing the path is  
> equivalent.)
> Of course, this is non-trivial.  But then neither is aggregating the  
> global table. :)

	how much of this could be mitigated if people properly announced
aggregates and used a provider-local no-export to balance their links
with them?  it does make those policies more complicated than the
simple cut+paste examples that they've likely used in the past, but
could possibly allow the "traffic-eng" with their upstream without
the global pollution.

	- jared

Jared Mauch  | pgp key available via finger from jared at
clue++;      |  My statements are only mine.

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