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How to find out device name (ADSL modem connected via Ethernet) in Linux/Ubuntu? The name is required for using tcpdump, the connection is active and was created in UI.

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migrated from serverfault.com Feb 6 '12 at 19:06

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That depends: if you are using PPPoE, it will be ppp${n}, where n is allocated starting at 0, and the first available number used for a new connection.

If you are using NAT, or direct IP, it will just be the eth${n} interface, and communication will be through TCP/IP as normal.

The easiest way to figure out the device is probably run ip route show and look for the "default" line - the dev part of that will tell you what device is used for your default (eg: "everything else") route:

daniel@ki:~$ ip route show
172.16.23.0/24 dev eth1  proto kernel  scope link  src 172.16.23.5 
default via 172.16.23.1 dev eth1 

In my example, my default route is via eth1.

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