The Dot1qEtherType allow administrator
to select a non-standard (other than 0x8100)
2-byte ethertype for the interface to
interoperate with third party vendor's system
that do not use the standard 0x8100 ethertype
to identify 802.1q-tagged frames.
The current administrative value of the
802.1q ethertype for the interface. The
administrative 802.1q ethertype value may
differ from the operational 802.1q ethertype
value. On some platforms, 802.1q ethertype
may be assigned per group rather than per port.
If multiple ports belong to a port group,
the 802.1q ethertype assigned to any of
the ports in such group will apply to all
ports in the same group.
To configure non-standard dot1q ethertype
is only recommended when the Cisco device
is connected to any third party vendor device.
Also be advised that the custom ethertype value
needs to be changed in the whole cloud of
Cisco device with the same custom ethertype
value if the third party device are separated
by number of Cisco device in the middle.