Question

finding unused vlans assigned to a port

  • 24 July 2019
  • 5 replies
  • 221 views

Is the "show fdb port x" command a fair way to figure out what vlans don't need to be tagged on that port?

5 replies

Userlevel 3
Is the "show fdb port x" command a fair way to figure out what vlans don't need to be tagged on that port?

If the FDB does not contain an entry for a VLAN then that all devices on that VLAN on that port are currently quiet (or there are no devices). So in short no, it is not a 100% guarantee.
Userlevel 6
there may be better ways to do this if you could be a bit more specific as to what problem you are trying to solve. If it network discovery. cleaning up configurations, trying to see adjacent port configurations match are a few things I can think about immediately and they could be done via mac table but may not give you the full picture and end result you are looking for.
@EtherMAN I'm trying to cleanup configurations. Like one port has 21 vlans tagged when it only needs two, so I'm trying to remove the vlans that are not needed.
Userlevel 2
A customer has written a Linux/MacOS script that scans the network for adjacent switches (via EDP and LLDP) and compares the ports. He checks for VLAN names that differ, if VLANs are present on both ends and so on, quite sophisticated. I cannot share the entire script (at least not without his consent), but I might be able to help you out a bit if that's a suitable solution for you.

/Fredrik
Userlevel 6
Sorry should have pinged me again also ... we do this the hard way ... show port info detail on each switch trunk port and compare.. Then of course you have to make sure vlan is not in use ... so this is a lengthy process at best but well worth the effort.

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