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.
[toc:faq]The ProblemOn traditional switches whenever we have a trunk
interface we use the VLAN tag to demultiplex the VLANs. The switch needs
to determine which MAC Address table to look in for a forwarding
decision. To do this we require the switch to do...
[toc:faq]Introduction:Netdr is a tool available on a RSP720, Sup720 or
Sup32 that allows one to capture packets on the RP or SP inband. The
netdr command can be used to capture both Tx and Rx packets in the
software switching path. This is not a substitut...
IntroductionOSPF, being a link-state protocol, allows for every router
in the network to know of every link and OSPF speaker in the entire
network. From this picture each router independently runs the Shortest
Path First (SPF) algorithm to determine the b...