It is possible to have a frame with a Null tag, i.e. it looks like it is on VLAN 0. It does this, just so that it can use the 3 bits for the CoS. The zero-VLAN means native, whatever that might be.
Cisco phones often use that technique. You can configure the port as an access port. The PC sends frames like it was on a normal access port. The telephone sends frames tagged with VLAN 0 and a CoS 5. These telephone frames are implicitly on the VLAN that you have configured on the port as the voice VLAN.
[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...