I have a remote private network connected to the internet via a Linux gateway. The gateway has the following arrangement:

  • eth0 - external IP
  • br0 - with eth1, and tap0 devices added to the bridge.

eth1 is the internal network, we'll call it eth1 serves DNS and DHCP. Everything is working perfectly on that internal network, clients get DHCP addresses and DNS works.

Now I want to ether bridge to the remote network from a local site. The local site consists of only two machines on another private network: local gateway and a client machine. So I've run on the local gateway:

ssh -o Tunnel=ethernet -w 0:0 root@remote.gateway

This partially works. There are no errors reported by ssh. The client machine acquires an IP address from the DHCP server, and can ping the server and perform DNS lookups however it can't communicate with any other machines on the remote private network (e.g. Remote server).

What do I need to do to tell the local/remote gateway that packets should be forwarded on to relevant remote machines?

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This didn't work because the VMWare virtual switch I was using for the remote server network was not in promiscuous mode. The ARP requests were getting as far as the remote server NIC, but never getting back to the gateway. So the answer was to configure the switch to allow promiscuous mode. In vSphere, with the host selected Manage -> Networking -> Virtual Switch -> edit.

More here: https://kb.vmware.com/s/article/1002934

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