Configuring EtherChannel and VLAN Trunks

EtherChannel port bundles allow you to increase the bandwidth of connections between devices by grouping multiple physical ports into a single virtual port.

VLAN trunks are point-to-point links that carry the traffic of multiple VLANs. Trunk ports are useful in the network backbone, where traffic from many VLANs is handled.

You can configure EtherChannel links as VLAN trunks, providing high-bandwidth connections to the network backbone.

To configure EtherChannel VLAN trunks on the switch, perform these tasks:

Step 1 Configure EtherChannel---Configure multiple ports between switches as a single virtual link.

Step 2 Configure VLAN Trunks---Configure the EtherChannel link as a trunk port to transport traffic for multiple VLANs.

Configure EtherChannel

EtherChannel port bundles provide increased bandwidth between network devices by grouping multiple Fast or Gigabit Ethernet ports into a single logical transmission path.

EtherChannel bundles contain contiguous ports (for example, ports 1-4 or ports 5-8) on a Fast or Gigabit EtherChannel-capable switching module. You can configure ports into bundles containing two or four ports (for example, two bundles using ports 1-2 and 3-4, or one bundle using ports 1-4).

You can configure ports to negotiate an EtherChannel bundle with the neighboring device automatically (using the auto and desirable modes), or you can place the ports in on mode on both ends of the link. Ports in on mode will not form a channel with ports in auto or desirable mode. By default, Fast and Gigabit Ethernet ports are in auto mode.

Note There are additional configuration restrictions associated with EtherChannel port bundles. For complete information, see the Software Configuration Guide for your switch.

To configure a group of Fast Ethernet or Gigabit Ethernet ports as an EtherChannel port bundle, perform this task in privileged mode:

Task Command

Step 1 If you are unsure which ports support EtherChannel or how the ports are grouped, verify the port groups for the module or switch you are configuring.

show port capabilities [mod_num[/port_num]]

Step 2 Create a channel on the desired ports.

set port channel mod_num/ports {on | off | auto | desirable}

Step 3 Verify the channeling configuration.

show port channel [mod_num[/port_num]] [info | statistics]

Task	Command
Step 1 If you are unsure which ports support EtherChannel or how the ports are grouped, verify the port groups for the module or switch you are configuring.	show port capabilities [mod_num[/port_num]]
Step 2 Create a channel on the desired ports.	set port channel mod_num/ports {on \| off \| auto \| desirable}
Step 3 Verify the channeling configuration.	show port channel [mod_num[/port_num]] [info \| statistics]

This example shows how to configure a two-port Gigabit EtherChannel bundle and how to verify the EtherChannel configuration (this example assumes that there are no configuration mismatches between the local and neighboring ports, and that the ports on the other end of the link are in auto or desirable mode):

Console> (enable) set port channel 2/1-2 desirable
Port(s) 2/1-2 channel mode set to desirable.
Console> (enable) show port channel
Port  Status     Channel   Channel     Neighbor                  Neighbor
                 mode      status      device                    port
----- ---------- --------- ----------- ------------------------- ---------- 
 2/1  connected  desirable channel     WS-C5509    003812064     1/1       
 2/2  connected  desirable channel     WS-C5509    003812064     1/2       
----- ---------- --------- ----------- ------------------------- ---------- 
Console> (enable)

Configure VLAN Trunks

VLAN trunks carry the traffic of multiple VLANs. Fast Ethernet and Gigabit Ethernet ports (including EtherChannel port bundles) can use Inter-Switch Link (ISL) or IEEE 802.1Q encapsulation for VLAN trunking. Other media use other encapsulation schemes (for example, LAN Emulation on ATM).

By default, Fast Ethernet and Gigabit Ethernet ports are in auto mode. If the port on the other end of the link is in desirable mode or on, a port in auto mode automatically becomes a trunk port.

The default trunk encapsulation depends on which encapsulation the hardware supports:

negotiate (on hardware supporting both ISL and 802.1Q)
isl (on hardware supporting ISL only)
dot1q (on hardware supporting 802.1Q only)

Note For complete information on the various trunk modes and encapsulation types, refer to the Software Configuration Guide for your switch.

To configure a Fast Ethernet or Gigabit Ethernet port as a trunk, perform this task in privileged mode:

Task Command

Step 1 If you are unsure which encapsulation types a port supports, verify the port capabilities.

show port capabilities [mod_num[/port_num]]

Step 2 Configure a Fast or a Gigabit Ethernet port as a trunk. If you are configuring an EtherChannel port bundle as a trunk, specify any one of the ports in the channel.

set trunk mod_num/port_num {on | desirable | auto} {isl | dot1q | negotiate}

Step 3 Verify that the trunk configuration is correct.

show trunk

Task	Command
Step 1 If you are unsure which encapsulation types a port supports, verify the port capabilities.	show port capabilities [mod_num[/port_num]]
Step 2 Configure a Fast or a Gigabit Ethernet port as a trunk. If you are configuring an EtherChannel port bundle as a trunk, specify any one of the ports in the channel.	set trunk mod_num/port_num {on \| desirable \| auto} {isl \| dot1q \| negotiate}
Step 3 Verify that the trunk configuration is correct.	show trunk

This example shows how to configure a port to become a trunk and how to verify the trunk configuration (this example assumes that the port on the other end of the link is in auto, desirable, or on mode and supports IEEE 802.1Q encapsulation):

Console> (enable) set trunk 2/1 desirable dot1q
Port(s) 2/1-2 trunk mode set to desirable.
Port(s) 2/1-2 trunk type set to dot1q.
Console> (enable) show trunk
Port      Mode         Encapsulation  Status        Native vlan
--------  -----------  -------------  ------------  -----------
 2/1      desirable    dot1q          trunking      1
 2/2      desirable    dot1q          trunking      1
 
Port      Vlans allowed on trunk
--------  ---------------------------------------------------------------------
 2/1      1-1005
 2/2      1-1005
 
Port      Vlans allowed and active in management domain 
--------  ---------------------------------------------------------------------
 2/1      1,10,20,30,40,50,60
 2/2      1,10,20,30,40,50,60
 
Port      Vlans in spanning tree forwarding state and not pruned
--------  ---------------------------------------------------------------------
 2/1      1,10,20,30,40,50,60
 2/2      1,10,20,30,40,50,60
Console> (enable)

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