Routing with Linux Bridge Flat Network

asked 2016-11-03 03:03:42 -0600

adityavajjha gravatar image

updated 2016-11-03 09:56:28 -0600

Hello,

I have a Liberty Setup on CentOS 7 on Cisco UCS C Series servers. I am trying to use the Linux Bridge Mech driver and flat network type driver.

My scenario is that I have need to create a Flat Tenant Network which has the subnet 192.168.200.0/24. The compute nodes' NICs are all in the 192.168.100.0/24 space. The compute node itself (from the CentOS command line) is able to reach IPs in the 192.168.200.0/24 space including the gateway. But when I create a VM in this same network, they are not able to go out to the gateway or other endpoints in this space. When I run tcpdump on the compute node, I see that the VM is sending out ARP requests, but there is no response.

This looks like the "Routed Mode" in KVM. Is this kind of a setup even allowed? Do Linux Bridges forward traffic which is not in the same network as the physical NIC that they are connected to?

My understanding was that since the Linux Bridge is an L2 device, it wouldn't care which IP the VM is on and would just forward/broadcast packets. Please correct me if I am wrong.

Any help is highly appreciated.

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