Mapping IP -> ASN

Alex.Bligh amb at
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 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.)


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,
or the cern router.


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

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