Cisco Tips & Tricks

May 28, 2006

Finding Anouncing AS of an IP

Filed under: bgp, IP Routing, Router — ciscotips @ 11:50 pm

If you are a network engineer working for a backbone ISP team, you would always like to know which autonomous system (AS) announces a given IP address. One way to do this is by querying the whois server of a routing registry such as RADB or RIPE, and looking for the origin attribute of a route object. However, not all networks properly register their route objects, so the information might not be available or may be outdated.

Another method is by looking at the actual BGP route table for the origin AS of a prefix. You could do this on your own BGP speaking routers or on a public route server with the "show ip bgp" command (or equivalent), or by using one of the public looking glasses on the web. However, this method is cumbersome, especially if you want to quickly look up something or if you have a large number of addresses that you want to analyze with a script.

Yet there is another  service which was announced by the RIPE RIS project. Their whois server can be queried using "whois -h riswhois.ripe.net", and returns results in RPSL like format (as used by the RIPE whois database itself). The data is gathered from route collector boxes in various locations. For more information about this service, see this web page

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