Listen only NIC configuration on Linux

answered 2020-01-21 07:42:45 +0000

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Partly. Bring up the interface without any IP(4/6) address assigned, nor start a DHCP or other network configuration client of course, to have an idle interface which is not likely to send out any frames.

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Very interesting - I never even thought of that, I think my head just exploded. So basically put a NIC on the net with no IP address and open it in promiscuous mode and sniff away. Interesting, I hadn't considered they would still listen if not configured.

Suppose I had a NIC that needed to be on a certain IP address - say for output from the local cable router DMZ. What then, back to the no gateway scheme?

WoodyW ( 2020-01-21 07:51:45 +0000 )edit

Actually no - again! Open in promiscuous mode and filter the the IP address I'm interested in from the router DMZ. Thanks for some good ideas.

WoodyW ( 2020-01-21 07:57:40 +0000 )edit

OK, fantastic - but how does this impact the construction of the local ARP table - if there's no entry in the ARP table for the "quiet" NIC does the switch just flood the clients hoping someone is listening (which we would be) or reject the packet outright?

WoodyW ( 2020-01-21 08:06:45 +0000 )edit

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Listen only NIC configuration on Linux