Bridge is not forwarding DHCP reply

Question

My setup is as following: Using kvm and tap-interfaces I have two vms running. The two tap-interfaces are connected via a bridge. On tap0 I have a DHCP-server running, on tap1 I executed a "dhclient". Using tcpdump I got to know that tap1 sends a request, which is received by the server. The server replies. I can see the reply on the bridge interface, however the reply never gets to the client.

Also if I assign an IP to the client manually, I'm not able to ping in neither direction (server-client, client-server)

I have also tried setting all to 0 in /proc/sys/net/bridge/

Any help would be appreciated.

Answer 1

When you junction interfaces into a bridge, you no longer use the individual interfaces but the entire bridge as an interface. You probably need to change your DHCP server to listen on br0 instead of tap0.

If you don't have a br0 or other similar bridge interface setup, you need to make one when you're using tap interfaces. See the brctl command's man page.