4000 Switch

4000 Switch
To configure a trunk on a 4000 series switch, use the set trunk command, and on the IOS-based
switch, use the trunk on command:
Terry_4000> (enable) set trunk 2/12 ?
Usage: set trunk <mod_num/port_num>
[on|off|desirable|auto|nonegotiate] [vlans] [trunk_type]
(vlans = 1..1005 An example of vlans is 2-10,1005)
(trunk_type = isl,dot1q,dot10,lane,negotiate)
Terry_4000> (enable) set trunk 2/12 on isl
Port(s) 2/12 trunk mode set to on.
Port(s) 2/12 trunk type set to isl.
Terry_4000> (enable) 2003 Mar 21 06:31:54
%DTP-5-TRUNKPORTON:Port 2/12 has become isl trunk
Port 2/12 has become a trunk port that uses ISL encapsulation. Notice that we did not specify
the VLANs to trunk. By default, all VLANs would be trunked. Take a look at a configuration
in which we specified the VLANs to use:
Terry_4000> (enable) set trunk 2/12 on 1-5 isl
Adding vlans 1-5 to allowed list.
462 Chapter 14  VLANs, Trunks

Please use the 'clear trunk' command to remove
vlans from allowed list.
Port(s) 2/12 allowed vlans modified to 1-1005.
Port(s) 2/12 trunk mode set to on.
Port(s) 2/12 trunk type set to isl.
Notice that, even though we told the switch to use VLANs 1–5, it added 1–1005 by default. To
remove VLANs from a trunk port, use the clear vlan command. We’ll do that in a minute.
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 respond only to trunk requests), two ports will never become a trunk
if both of them are set to auto.
nonegotiate Makes a port a permanent trunk port, but because the port does not use DTP
frames for communication, there is no negotiation. 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 enables the port to be trunked, but you won’t be sent any DTP frames.
Be careful when using the nonegotiate option. It is not unusual to set up
switches initially with auto or desirable trunks and then lock them down with
on, after the switch fabric has settled down. If two trunk ports are configured
with auto or desirable, they need to receive the negotiate packets to tell that
there is another trunk-capable device on the other side. If both trunk ports are
set to desirable but nonegotiate, no trunk will come up.