Troubleshooting Trunking
Troubleshooting trunking links happens mostly at the physical and datalink
layers. Start with the most basic assumptions and work your way “up” the
OSI model. It is important to show that physical layer connectivity is
present, before moving on to, for instance before trying to troubleshoot IP
problems.
■ Are both sides of the link in the correct trunking mode?
■ Is the same trunk encapsulation on both sides?
■ If 802.1Q, is the same native VLAN on both sides?
■ Are the same VLANs permitted on both sides?