One basic question that i have is
When CDP packets are exchanged between two switches on a trunk link with a native vlan 1, i presume that the CDP packets go untagged with a vlan of 1. Now, when i remove vlan 1 from the trunk link and replace the native vlan with, say, vlan 4. Shouldn't the CDP packets go on vlan 4?
I have configured for monitor session on that trunk port ( with encapsulation so i can see which vlan is CDP part of) and my destination contains a pc with a realtek card with which i can see the tagged packets from those mirrored ports.
Even after I remove Vlan 1 and replace the native vlan as 4, i still see my CDP packets tagged with vlan 1. Any reason why?
Just to double check i set up an ip address for vlan 4 on both the switches and sent out an ICMP from one to the another. I could see that the ICMP packets were correctly tagged as vlan 4.
-/ Kiran Cherian
Vlan 1 could not be fully removed. Even if vlan 1 is pruned from trunk, the control packet will be still sent in vlan 1. This is expected behavior in Cisco switch.
Control protocols like CDP, VTP, PAGP are always sent on vlan 1 for cisco switches no what what native vlan is.
If vlan 1 is not native vlan, those control packet will be tagged as vlan 1. V