North American Network Operators Group
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Re: URPF on small BGP-enabled customers?

  • From: Patrick W. Gilmore
  • Date: Fri Jun 03 10:29:23 2005 
On Jun 3, 2005, at 9:30 AM, [email protected] wrote:
At an old transit provider I was at, we had a pig of a time dealing with
uRPF. It doesn't like asymmetric routing at all, which is commonplace when
you've got customers homed at exchange points for one.

I imagine the simplest and most foolproof way around directly connected
providers blackholing your traffic is announcing more specific prefixes
down the one you're currently favourint, and just the aggregates for same
into the second. Good luck if you've only got a bunch of non- contiguous
/24s..
<disclaimer> Not uRPG guru </disclaimer>

Why would that work? If I see a /16 from my customer and a /19 from a peer, I will still pick the /19, and strict uRPF should drop any packets from that /19 coming the customer interface, right?

Not to mention the Really Bad Things associated with deaggregation.

Perhaps a simpler way is to announce your entire allocation and put no-export on things you want to come in your other provider? ^1239$ will still pick those routes, but no one else will see them. Although sprint is a _VERY_ large network when you include downstreams, their own AS is rather tiny compared to the whole Internet.

--
TTFN,
patrick