(vlans = 1..1005 An example of vlans is 2−10,1005)
(trunk_type = isl,dot1q,dot10,lane,negotiate)
The different port negotiation types are described in Table 5.1, and the different trunk encapsulation types are
described in Table 5.2.
Table 5.1: Port negotiation syntaxes for configuring VLAN trunks.
Variable Description
auto This trunking mode is used if the port uses DISL to
initiate trunking. This is the default mode for Fast
Ethernet and mimics plug−and−play. You cannot
configure a trunk when both ends’ switch ports are
configured for auto mode. One switch must be set to
on or desirable mode.
desirable This trunking mode, if using DISL, actively tries to
configure itself as a trunk link. The other end of the
trunk link must be configured to on or desirable to
complete the trunk initiation.
off This option disables the port from becoming a trunk.
It is typically used when the device on the other end
does not support ISL or IEEE 802.1Q. The port on the
other end might be a 10Mbps Ether port or FDDI
interface.
on This option basically makes the port a trunk port,
whether the other end is configured to be or cannot
become a trunk. Use this option when the port on the
other end does not understand DTP, such as a
third−party adapter.
nonegotiate Use this option when DISL negotiation that takes
place on ISL trunks is not supported. When using
dot1q as the final parameter, this option tells the
switch that ISL will not be used for trunking the ports.
Table 5.2: Encapsulation type syntaxes that can be used when configuring VLAN trunk links.
Variable Description
isl Applies the ISL protocol encapsulation to an Ethernet
trunk.
dot1q Used for Ethernet trunks using the IEEE 802.1Q
standard.
dot10 Used when assigning a FDDI trunk link to the port.
lane Used when applying ATM to a trunk link port.
negotiate Puts the port into permanent trunking mode. This
option disallows the port from generating DTP
frames. Typically, this command is used with
switch−to−router trunks.
Let’s set port 2/1 as a trunk link using ISL with the following command:
5000> (enable) set trunk 2/1 on isl
Port(s) 2/1 trunk mode set to on.
Port(s) 2/1 trunk type set to isl.
5000> (enable) 2000 Dec 21 05:12:01 %DTP−5−TRUNKPORTON:Port 2/1 has
become trunked.
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