Information Technology Reference
In-Depth Information
Configuring EtherChannel Switch-to-Switch Connections on
Catalyst 4000/5000/6000 Switches
EtherChannel allows multiple physical Fast Ethernet or Gigabit Ethernet links to be combined into one
logical channel. This allows load-sharing of traffic among the links in the channel, as well as redundancy
in case one or more links in the channel fail. EtherChannel can be used to interconnect LAN switches,
routers, servers, and clients via unshielded twisted-pair (UTP) wiring or single-mode and multimode
fiber.
EtherChannel is an easy way to aggregate bandwidth between critical networking devices. On the
Catalyst 5000, a channel can be created from two ports, making it a 200-Mbps link (400 Mbps
full-duplex), or four ports, making it a 400-Mbps link (800 Mbps full-duplex). Some cards and platforms
also support Gigabit EtherChannel and have the capability to use from two to eight ports in an
EtherChannel. The concept is the same, no matter what speeds or number of links are involved.
Normally, the Spanning-Tree Protocol would consider these redundant links between two devices to be
loops and would cause the redundant links to be in blocking mode, effectively making these links
inactive (providing only backup capabilities in case the main link fails). When using IOS 3.1.1 or greater,
Spanning-Tree Protocol treats the channel as one big link, so all the ports in the channel can be active at
the same time.
This section takes you through the steps for configuring EtherChannel between two Catalyst 5000
switches and shows you the results of the commands as they are executed. Catalyst 4000 and 6000
switches could have been used in the scenarios presented in this document to obtain the same results.
For the Catalyst 2900XL and 1900/2820, the command syntax is different, but the EtherChannel
concepts are the same.
EtherChannel may be configured manually by typing in the appropriate commands, or it may be
configured automatically by having the switch negotiate the channel with the other side using the Port
Aggregation Protocol (PAgP). It is recommended to use PAgP desirable mode to configure EtherChannel
whenever possible because manually configuring EtherChannel can create some complications. This
section gives examples of configuring EtherChannel manually and examples of configuring
EtherChannel by using PAgP. Also included is how to troubleshoot EtherChannel and how to use
trunking with EtherChannel. In this chapter, the terms
EtherChannel
,
Fast EtherChannel
,
Gigabit
EtherChannel
, and
channel
will all refer to EtherChannel.
Contents
The following topics will be covered in this section:
•
Tasks for manually configuring EtherChannel
•
Verifying the EtherChannel configuration
•
Using PAgP to automatically configure EtherChannel (preferred method)
•
Trunking and EtherChannel
•
Troubleshooting EtherChannel
•
Commands used in this section
Figure 23-6 illustrates our test environment. The configuration of the switches has been cleared using
the
clear config all
command. Then the prompt was changed using
set system name
. An IP address and
mask were assigned to the switch for management purposes using
set int sc0 172.16.84.6 255.255.255.0
for Switch A and
set int sc0 172.16.84.17 255.255.255.0
for Switch B. A default gateway was assigned
to both switches using
set ip route default 172.16.84.1
.
