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Chapter 3
VLANs
We need to explain the different options for turning up a trunk port:
On The switch port is a permanent trunk port regardless of the other
end. If you use the on state, you must specify the frame tagging method
because it will not negotiate with the other end.
Off The port becomes a permanent non-trunk link.
Desirable The port you want to trunk becomes a trunk port only if the
neighbor port is a trunk port set to on, desirable, or auto.
Auto The port wants to become a trunk port but becomes a trunk only
if the neighbor port asked the port to be a trunk. This is the default for all
ports. However, because auto switch ports will never ask (they only
respond to trunk requests), two ports will never become a trunk if they are
both set to auto.
Nonegotiate Makes a port a permanent trunk port, but the port does
not use DTP frames for communication. If you're having DTP problems
with a switch port connected to a non-switch device, then use the
nonegotiate
command when using the set trunk command. This will
allow the port to be trunked, but you won't be sent any DTP frames.
1900 Switch
The 1900 switch has the same options but runs only the DISL encapsulation
method:
1900EN#config t
Enter configuration commands, one per line.
End with CNTL/Z
1900EN(config)#int f0/26
1900EN(config-if)#trunk ?
auto Set DISL state to AUTO
desirable Set DISL state to DESIRABLE
nonegotiate Set DISL state to NONEGOTIATE
off Set DISL state to OFF
on Set DISL state to ON
1900EN(config-if)#trunk auto
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