How to get the infromation of trunk vlan from wireshark

A vlan10 SVI on the Cat 3750 is pinging the vlan 20 SVI on the Cat 3560, and the vlan 10 SVI on the Cat 3560 is pinging the vlan 20 SVI on the Cat 3750.

On the Cat 3750:

monitor session 10 source int fa1/0/46
monitor session 10 destination int fa1/0/33 encapsulation replicate

As others have mentioned, on 3750 you need "encapsulation replicate". Also, the monitor port fa1/0/33 had to be a dot1q trunk, just like the actual trunk port fa1/0/46


https://learningnetwork.cisco.com/docs/DOC-15413