bgp hints - internet routing news, hints and tips

Updated: 2003-11-06

Category: Tools

Quickly find the announcing AS of an IP address

In the course of network operations, one sometimes would 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 However, not all networks properly register their route objects, so the information might not be available or may be outdated.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.

Team Cymru (known for its bogon prefix list) has made a whois server available which provides the announcing AS number and name for any given IP address. The information in its database is based on 17 BGP feeds and is updated twice per hour. If your operating system has a command-line whois client, simply type "whois -h whois.cymru.com" followed on the same line by the IP address you would like to look up.

In addition to simple lookups as described above, the server also supports comments and multiple addresses per query. Both of these features are especially useful if you have a script to analyze a large number of IP addresses from a script. For more information about these features, see the server's web page or type "whois -h whois.cymru.com help".

Update: A similar service 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.

If you have any questions or comments regarding this article, please contact bgp@ruud.org.