Testing MAC Learning in the NSX L2 Bridge

Testing MAC Learning in the NSX L2 Bridge

One of our customers is preparing to migrate Virtual Machines from VLAN to VXLAN with the NSX L2 Bridge and asked me how to test the L2 Bridge and get confirmation that it is actually configured correctly and operational. All commands in this blog post are from the NSX Troubleshooting Documentation.

We can test if a bridge is functional by issuing a command on the NSX Manager.

show logical-router controller controllerID dlr dlrID bridge (all | bridgeID) mac-address-table

This command shows the mac address table for bridges configured on a logical router. This information is retrieved from the specified controller. Use all to show the mac address table for all bridges, or use bridgeID to show the mac address table for a specific bridge.

Note that we do not need to enable MAC learning on the attached logical switch.

Below is an example of the output from my lab. The first command shows the MAC address table from VLAN 2 and the second the MAC address from VLAN 20. The bridge (bridge ID 2) for VLAN 2 does not yet contains a VM in a bridged Logical Switch (VXLAN), the bridge (bridge ID 1) does have a VM in a bridged Logical Switch (VXLAN). This shows that you don’t need to have a VM running in the bridge before you can test this.

MAC address table NSX L2 Bridge

In the screenshot below the arp table from a Windows 7 VM in VLAN 20 to compare.

MAC address table Windows 7

This confirms that the NSX L2 Bridge is learning MAC addresses and working correctly.