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RE: BGP Filtering

  • From: Ben Butler
  • Date: Tue Jan 15 11:41:19 2008


Default wont work - I do care about my transit providers network
becoming partitioned or IXPs having problems or fiber cuts etc etc

So I need my router to see all the reachability of a prefix in BGP so
that my router knows which transit to send it to.

Defaults wont work because a routing decision has to be made, my transit
originating a default or me pointing a default at them does not
guarantee the reachability of all prefixes..

But if I can see the /19 in the table, do I care about a load of /24s
because the whole of the /19 should be reachable as the origin AS is
announcing it somewhere in their network and it is being received my a
transit so should be reachable.

Ok, I can dream up a few emergencies where it might be helpful to pin a
/24 as well as the /19 - but I am sure there aren't 100K+ emergencies
happening continuously in the route table and it is on the whole general
whatever because there is no incentive to stop de-aggregating once you
have started.

If they are only announcing the de-aggregated /24s and no summary /19
then my question doesn't apply as I only want to drop the more specifics
where a less specific exists.

I am struggling to see a defensible position for why just shy of 50% of
all routes appears to be mostly comprised of de-aggregated routes when
aggregation is one of the aims RIRs make the LIRs strive to achieve.  If
we cant clean the mess up because there is no incentive than cant I
simply ignore the duplicates.



-----Original Message-----
From: Jared Mauch [mailto:[email protected]] 
Sent: 15 January 2008 16:19
To: Ben Butler
Cc: [email protected]
Subject: Re: BGP Filtering

On Tue, Jan 15, 2008 at 04:11:36PM -0000, Ben Butler wrote:
> As a transit consumer - why would I want to carry all this cr*p in my 
> routing table, I would still be getting a BGP route to the larger 
> prefix anyway - let my transit feeds sort out which route they use & 
> traffic engineering.

	Well, you could always just take "Customer" routes from each of
your providers (since you're running BGP I presume you're actually
multihomed and not adding to the pollution) and point default at
one/both providers for the other networks (or take default from one or
both of them).

	- jared

Jared Mauch  | pgp key available via finger from [email protected]
clue++;      |  My statements are only