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

  • From: Patrick W. Gilmore
  • Date: Fri Oct 13 15:49:23 2006

On Oct 13, 2006, at 3:26 PM, Jared Mauch wrote:
On Fri, Oct 13, 2006 at 03:14:38PM -0400, Patrick W. Gilmore wrote:

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

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.
Sorry if I wasn't clear before, but I consider path info _just for your first hop upstream_ superfluous for the rest of the Internet. Does anyone think this is an unreasonable restriction?

More important question: How many people are doing TE or something and not applying no-export when they could? If you need help fixing that, or even figuring out if you need to fix it, I guarantee you several people on this list would help you, many for free.

This is one of the reasons things become "non-trivial". How do you prove that a disgregate prefix is useless to anyone except that one network?

I do not think it is impossible. But it certain ain't easy.