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I have created a tap device tap0 address 10.2.1.4 and added it to a host bridge br1 with address 10.2.1.1

I have "nc 10.2.1.4 -l 1234" running on the host and from another machine I do a "nc 10.2.1.4 1234".

tcpdump -i tap0 doesn't show any of the traffic. The traffic is shows up when I do "tcpdump -i br1"

What do I have to do to make the traffic showup on tap0.

user199098
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2 Answers2

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Usually bridged interface can not be an endpoint receiving traffic and directing it up to protocol stack of host machine. As soon as a bridge is added it is responsible for this sort of work itself.

FYI: http://www.microhowto.info/howto/bridge_traffic_between_two_or_more_ethernet_interfaces_on_linux.html#idp24240

Tap is a special logical interface which is represented and accessible internally. Hint: remove tap0 from the bridge and it will remain to be accessible from other hosts.

Thus, datapath is: Network -> eth0 -> br1 -> Stack TCP/IP -> Application

You can see traffic on tap0 if:

  • It is broadcast.
  • It is routed, say tap0 is used in a tunnel or VM connection.
Veniamin
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If you want to force tap0 to recieve its own IP packets, you may use ebtables. When packets are DROPed in the ethernet layer of tap0 at broute table, these packets go into the the IP layer of tap0 instead of eth0. See also: http://ebtables.sourceforge.net/examples/real.html#example1

If you just want more addresses for your host, use ip address add ....

Sherwood Wang
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