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This chapter describes how to use the command-line interface (CLI) to configure EtherChannel on the Catalyst 6000 and 6500 series switches. The configuration tasks in this chapter apply to Ethernet, Fast Ethernet, and Gigabit Ethernet switching modules, as well as to the uplink ports on the supervisor engine.
This chapter consists of these sections:
EtherChannel provides parallel bandwidth of up to 1600 Mbps (Fast EtherChannel full duplex) or 16 Gbps (Gigabit EtherChannel) between a Catalyst 6000 or 6500 series switch and another switch or host by grouping multiple Fast or Gigabit Ethernet interfaces into single logical transmission paths.
A Catalyst 6000 or 6500 series switch supports a maximum of 128 EtherChannels. You can form an EtherChannel with up to eight compatibly configured Ethernet ports on any module in a Catalyst 6000 or 6500 series switch. All ports in each EtherChannel must be the same speed.
Inbound broadcast and multicast packets on one segment in an EtherChannel are blocked from returning on any other segment of the EtherChannel. Outbound broadcast and multicast packets are sent through only one EtherChannel segment.
If a segment within an EtherChannel fails, traffic previously carried over the failed link switches to the remaining segments within the EtherChannel. A trap is sent upon a failure identifying the switch, the EtherChannel, and the failed link.
Configuring an EtherChannel creates an administrative group, designated by an integer between 1 and 1024, to which the EtherChannel belongs. When an administrative group is created, you can assign an administrative group number or let the next available administrative group number be assigned automatically. Forming a channel without specifying an administrative group number creates a new automatically numbered administrative group. An administrative group may contain a maximum of eight ports.
Each EtherChannel is automatically assigned a unique EtherChannel ID. Use the show channel group admin_group command to display the EtherChannel ID.
The Port Aggregation Protocol (PAgP) facilitates the automatic creation of EtherChannels by exchanging packets between Ethernet ports. PAgP packets are exchanged only between ports in auto and desirable modes. Ports configured in on or off mode do not exchange PAgP packets. The protocol learns the capabilities of port groups dynamically and informs the other ports. Once PAgP identifies correctly matched EtherChannel links, it groups the ports into an EtherChannel. The EtherChannel is then added to the spanning tree as a single bridge port.
EtherChannel includes four user-configurable modes: on, off, auto, and desirable. Only auto and desirable are PAgP modes. The auto and desirable modes can be modified with the silent and non-silent keywords. By default, ports are in auto silent mode.
Table 5-1 describes EtherChannel modes.
| Mode | Description |
|---|---|
on | Forces the port to channel without PAgP. With the on mode, a usable EtherChannel exists only when a port group in on mode is connected to another port group in on mode. |
off | Prevents the port from channeling. |
auto | PAgP mode that places a port into a passive negotiating state, in which the port responds to PAgP packets it receives but does not initiate PAgP packet negotiation. (Default) |
desirable | PAgP mode that places a port into an active negotiating state, in which the port initiates negotiations with other ports by sending PAgP packets. |
silent | Use this keyword with the auto or desirable mode when no traffic is expected from the other device to prevent the link from being reported to STP as down. (Default) |
non-silent | Use this keyword with the auto or desirable mode when traffic is expected from the other device. |
Both the auto and desirable modes allow ports to negotiate with connected ports to determine if they can form an EtherChannel, based on criteria such as port speed, trunking state, VLAN numbers.
Ports can form an EtherChannel when they are in different PAgP modes as long as the modes are compatible. For example:
If improperly configured, some EtherChannel ports are disabled automatically to avoid network loops and other problems. Follow these guidelines to avoid configuration problems:
Make sure that the ports are configured correctly. (See the "EtherChannel Configuration Guidelines" section.)
To configure EtherChannel on a group of Ethernet ports, perform this task in privileged mode:
| Task | Command |
|---|---|
Create the EtherChannel on the desired ports. | set port channel mod/ports... [admin_group] |
This example shows how to create a six-port EtherChannel in a new administrative group:
Console> (enable) set port channel 2/2-8 desirable Ports 2/2-8 left admin_group 1. Ports 2/2-8 joined admin_group 2. admin_group Ports ----------- ------------------------------------------------- 1 1/1-2 2 2/2-8 Ports 2/2-8 channel mode set to desirable. Console> (enable)
To add ports to an administrative group, perform this task in privileged mode:
| Task | Command |
|---|---|
Add ports to an Administrative group. | set port channel mod/ports... [admin_group] |
This example shows how to add a port to administrative group 2:
Console> (enable) set port channel 2/1 2 desirable Ports 2/1 left admin_group 1. Ports 2/1 joined admin_group 2. admin_group Ports ----------- ------------------------------------------------- 1 1/1-2 2 2/1-8 Ports 2/1 channel mode set to desirable. Console> (enable)
To change a port's mode, perform this task in privileged mode:
| Task | Command |
|---|---|
Change a port's mode. | set port channel mod/ports... [admin_group] |
This example shows how to change port 2/1 to auto mode:
Console> (enable) set port channel 2/1 mode auto Ports 2/1 channel mode set to auto. Console> (enable)
To set the EtherChannel port path cost, perform this task in privileged mode:
| Task | Command |
|---|---|
Step 1 Use the administrative group number to display the EtherChannel ID. | show channel group admin_group |
Step 2 Use the EtherChannel ID to set the EtherChannel port path cost. | set channel cost {channel_id | all} cost cost |
This example shows how to set the EtherChannel port path cost for channel ID 768:
Console> (enable) show channel group 20
Port Status Channel Admin Ch Neighbor Neighbor
Mode Group id Device Port
----- ---------- --------- ----- ---- ------------------------------------ -----
6/1 connected auto 20 768 WS-CONSTEL 2/1
6/2 connected auto 20 768 WS-CONSTEL 2/2
6/3 connected auto 20 768 WS-CONSTEL 2/3
6/4 connected auto 20 768 WS-CONSTEL 2/4
Console> (enable) set channel cost 768 cost 12
Port(s) 6/1-4 port path cost are updated to 31.
Channel 768 cost is set to 12.
Warning:channel cost may not be applicable if channel is broken.
Console> (enable)
To set the EtherChannel VLAN cost, perform this task in privileged mode:
| Task | Command |
|---|---|
Step 1 Use the administrative group number to display the EtherChannel ID. | show channel group admin_group |
Step 2 Use the EtherChannel ID to set the EtherChannel VLAN cost. | set channel vlancost channel_id cost |
This example shows how to set the EtherChannel VLAN cost for channel ID 768:
Console> (enable) show channel group 20
Port Status Channel Admin Ch Neighbor Neighbor
Mode Group id Device Port
----- ---------- --------- ----- ---- ------------------------------------ -----
6/1 connected auto 20 768 WS-CONSTEL 2/1
6/2 connected auto 20 768 WS-CONSTEL 2/2
6/3 connected auto 20 768 WS-CONSTEL 2/3
6/4 connected auto 20 768 WS-CONSTEL 2/4
Console> (enable) set channel vlancost 768 12
Channel 768 vlancost set to 12.
Console> (enable)
To disable an EtherChannel, perform this task in privileged mode:
| Task | Command |
|---|---|
Disable an EtherChannel. | set port channel mod_num/port_num off |
This example shows how to disable the EtherChannel:
Console> (enable) set port channel 2/2-8 off Ports 2/2-8 channel mode set to off. Console> (enable)
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