Trunking Header Tells Switch2 What to Do
Now, switch2 knows how to process each received frame. When it
receives frames in port FastEthernet 24, it expects to see a trunking header,
which identifies the VLAN. That tells switch2 which address table to use.
When switch2 needs to send frames out port Fa24 to switch1,
switch2 also adds a VLAN trunking header, knowing that switch1 expects to be
able to find the header to identify the right VLAN.
So, now to the other use of the term trunk, along with some related
terms. The term VLAN trunk, or sometimes simply
trunk, refers to a link between two switches over
which the additional trunking header is added, as in
Figure 7-9. The term VLAN trunking, or
simply trunking, refers to the process
of adding (when sending) and removing (upon receipt) the extra headers that
identify the VLANs.