The sys admin's daily grind: ASN

Charly's Column – ASN

Article from Issue 254/2022
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When digging into BGP routing information, Charly avoids the highway through parameter hell thanks to the ASN tool. In addition to a system's AS number, ASN delivers other information, such as its peering partners upstream and downstream.

Every admin knows how to deal with IP addresses. Unfortunately, IPs never turn up alone. They belong to a network, and the network is almost always assigned to an autonomous system (AS), which uses the Border Gateway Protocol (BGP) to exchange routing information.

There is a simple way to find out which AS a particular individual IP belongs to. By way of an example, the following is the IP address of Computec Media's web server, www.computec.de. The associated IP address 62.146.104.133 can be discovered using dig or by simply pinging.

I then feed this IP address to a tool named ASN [1]. The shell script aggregates the output of several other tools and presents the results in a clear-cut way. It has a number of dependencies that vary depending on the distribution you are using. What exactly needs to be installed for ASN to work is explained in a separate section on the tool's GitHub page.

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