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Identifying VLANs allowed on an 802.1q trunk via packet capture

I have a client with servers connecting to my Cisco Nexus switches on trunked interfaces.  The switch ports are configured with a native VLAN, being the server's primary VLAN for PXE boot, and a second VLAN for VM clients.  The client would like to be able to identify the VLANs allowed on the trunk from the server-end, so he can verify the configuration when troubleshooting PXE boot or VM connectivity issues. 

Is there a protocol that is transmitted, or can be transmitted, in broadcast that should allow a packet capture to reveal all VLANs permitted on a trunk?  I know we can learn the native VLAN, but I'm looking for a way for the server to "hear" the whole VLAN range.

everyone's help is greatly appreciated.

Dan

  • LAN Switching and Routing
1 REPLY

Identifying VLANs allowed on an 802.1q trunk via packet capture

Hi Daniel,

if I understand your question well, I believe this is you're looking for: LLDP (Link Layer Discovery Protocol).

http://www.cisco.com/en/US/docs/switches/blades/3030/software/release/12.2_37_se/configuration_/guide/swlldp.html

http://en.wikipedia.org/wiki/Link_Layer_Discovery_Protocol

Regards.

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