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Cisco Catalyst Switch Module 3110 and 3012 for IBM BladeCenter Software Configuration Guide
OL-12189-01
Chapter 12 Configuring VLANs
Configuring VLAN Trunks
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STP Port Fast setting.
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trunk status: if one port in a port group ceases to be a trunk, all ports cease to be trunks.
• We recommend that you configure no more than 24 trunk ports in PVST mode and no more than 40
trunk ports in MST mode.
• If you try to enable IEEE 802.1x on a trunk port, an error message appears, and IEEE 802.1x is not
enabled. If you try to change the mode of an IEEE 802.1x-enabled port to trunk, the port mode is
not changed.
• A port in dynamic mode can negotiate with its neighbor to become a trunk port. If you try to enable
IEEE 802.1x on a dynamic port, an error message appears, and IEEE 802.1x is not enabled. If you
try to change the mode of an IEEE 802.1x-enabled port to dynamic, the port mode is not changed.
Configuring a Trunk Port
Beginning in privileged EXEC mode, follow these steps to configure a port as a trunk port:
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
interface interface-id Specify the port to be configured for trunking, and enter interface
configuration mode.
Step 3
switchport trunk encapsulation {isl |
dot1q | negotiate}
Configure the port to support ISL or IEEE 802.1Q encapsulation or to
negotiate (the default) with the neighboring interface for encapsulation
type.
You must configure each end of the link with the same encapsulation type.
Step 4
switchport mode {dynamic {auto |
desirable} | trunk}
Configure the interface as a Layer 2 trunk (required only if the interface
is a Layer 2 access port or tunnel port or to specify the trunking mode).
• dynamic auto—Set the interface to a trunk link if the neighboring
interface is set to trunk or desirable mode. This is the default.
• dynamic desirable—Set the interface to a trunk link if the
neighboring interface is set to trunk, desirable, or auto mode.
• trunk—Set the interface in permanent trunking mode and negotiate
to convert the link to a trunk link even if the neighboring interface is
not a trunk interface.
Step 5
switchport access vlan vlan-id (Optional) Specify the default VLAN, which is used if the interface stops
trunking.
Step 6
switchport trunk native vlan vlan-id Specify the native VLAN for IEEE 802.1Q trunks.
Step 7
end Return to privileged EXEC mode.
Step 8
show interfaces interface-id switchport Display the switchport configuration of the interface in the Administrative
Mode and the Administrative Trunking Encapsulation fields of the
display.
Step 9
show interfaces interface-id trunk Display the trunk configuration of the interface.
Step 10
copy running-config startup-config (Optional) Save your entries in the configuration file.