Mapping IP -> ASN

Fri Nov 15 17:30:38 UTC 1996

> Is there a tool available that will take an IP address and return the 
> ASN attached to that network? I've been in situations before where this 
> information would be useful, but not having access to the BGP routing 
> information I'm not sure how to do this? (I've looked around some 
> "likely" web sites - such as Merit - but haven't found anything.)
> 
> The pressing need is for the ASN associated with 198.161.92.0. This 
> network is connected to I*star, but I can't tell which of I*star's 
> three ASNs it's homed on. (And they aren't being responsive to queries.)

Practical:

Use show ip b n.n.n.n or equivalent on something carrying full routing.
If you don't have anything carrying full routing do the equivalent on
Digex's excellent MAE-East looking glass at http://nitrous.digex.net,
or the cern router.

Theoretical:

Alternatively find out which AS it's meant to be originated in by
looking at the origin attribute in the appropriate IRR using whois
(assuming it's registered).

Alex Bligh
Xara Networks