[e2e] determining ingress interface?
kc at caida.org
Tue Jul 2 18:00:09 PDT 2002
On Fri, Jun 21, 2002 at 09:12:33AM -0400, Rajesh Talpade wrote:
I asked this question on the NANOG mailing list.....
> Is there a way for an ISP to determine the ingress router interface at
> its network border that _should be_ passing IP traffic _from_ an IP
> address not owned by it? In other words, given an IP address, I would
> like to know what interface should be used by traffic from this address
> to enter my network.
> I realize the interface used may change over time.
....and got some answers....
> Use "traceroute -g" (Randy Bush, Buddy Bagga)
Issues: Not all ISPs allow it; is only useful for a few hops into peer
ISP networks, and for IP addresses belonging to peer ISPs
> Use traffic filters/logs on routers (Dylan Greene)
Issues: Requires instantiation on all border routers; requires traffic
from IP address to exist
> Use routes learned from peer ISP (Dylan Greene)
Issues: Requires assumption that paths are same in both directions
Is there work that answers the question without requiring the traffic to
exist or assuming same bi-directional paths, perhaps using BGP path info,
or data from CAIDA's skitter tool?
unfortunately i don't know of any,
it's one of those things i'd pay good money
to be wrong about though
you might find http://www.caida.org/tools/measurement/iffinder/
of interest (only marginally relevant but at least tries to
match interfaces to a single chassis)
would recommend against assumptions of either symmetric paths
or bgp reflecting actual traffic flow
unless you're writing science fiction
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