[e2e] determining ingress interface?

k claffy 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


More information about the end2end-interest mailing list