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This chapter describes how to configure Fast EtherChannel and Gigabit EtherChannel. The configuration tasks in this chapter apply to Ethernet, Fast Ethernet, and Gigabit Ethernet switch ports on switching modules and fixed-configuration switches, as well as to supervisor engine Fast Ethernet and Gigabit Ethernet uplink ports.
This chapter consists of these sections:
Fast EtherChannel provides parallel bandwidth of up to 800 Mbps (400-Mbps full duplex) between a switch and a router, host, or another switch by grouping multiple Fast Ethernet interfaces into a single logical transmission path.
Fast EtherChannel segments must be contiguous ports on a Fast EtherChannel-capable Fast Ethernet switching module. You can configure Fast Ethernet ports into Fast EtherChannel groups containing two or four ports, yielding 400- or 800-Mbps bidirectional bandwidth, respectively.
Gigabit EtherChannel provides parallel bandwidth of up to 8 Gbps (4 Gbps full duplex) between a switch and a router, host, or another switch by grouping multiple Gigabit Ethernet interfaces into a single logical transmission path.
You can configure Gigabit Ethernet ports into Gigabit EtherChannel groups containing two or four ports, yielding 4- or 8-Gbps bidirectional bandwidth, respectively.
Both Fast and Gigabit EtherChannel bundles can be configured as trunk links. For more information, refer to the "EtherChannel Configuration Guidelines and Restrictions" section and to "Configuring VLAN Trunks on Fast Ethernet and Gigabit Ethernet Ports."
The Port Aggregation Protocol (PAgP) facilitates the automatic creation of Fast EtherChannel and Gigabit EtherChannel links by exchanging packets between channel-capable ports. The protocol learns the capabilities of port groups dynamically and informs the neighboring ports.
After PAgP identifies correctly paired channel-capable links, it groups the ports into a channel. The channel is then added to the spanning tree as a single bridge port. Inbound broadcast and multicast packets on one segment in a channel are blocked from returning on any other segment of the channel. Outbound broadcast and multicast packets are sent through only one segment in the channel.
There are four user-configurable channel modes. Table 6-1 describes each mode. PAgP packets are exchanged only between ports in auto and desirable mode. Ports configured in on or off mode do not exchange PAgP packets. By default, ports are in auto mode.
| Mode | Description |
|---|---|
on | Forces the port to channel without negotiation. PAgP packets are not exchanged. The port is channeling regardless of how the peer port is configured. If the peer port is in on mode, a channel is formed. In any other mode, the peer port is placed in the errdisable state due to a channel misconfiguration. |
off | Prevents the port from channeling. PAgP packets are not exchanged. The port is not channeling regardless of how the peer port is configured. No channel is formed. |
auto | 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. A channel is formed only with another port group in desirable mode. (Default) |
desirable | Places a port into an active negotiating state, in which the port initiates negotiations with other ports by sending PAgP packets. A channel is formed with another port group in either desirable or auto mode. |
Both the auto and desirable modes allow ports to negotiate with connected ports to determine if they can form a channel, based on criteria such as port speed, trunking state, native VLAN, and so on.
Channel ports can be in different channel modes as long as the modes are compatible. A port in desirable mode can form a channel successfully with another port that is in desirable or auto mode. Similarly, a port in auto mode can form a channel with another port in desirable mode.
A port in auto mode cannot form a channel with another port that is also in auto mode, since neither port will initiate negotiation. In addition, a port in on mode can form a channel only with a port in on mode, because ports in on mode do not exchange PAgP packets.
If a segment within a channel fails, traffic previously carried over the failed link switches to the remaining segments within the channel. A trap is sent upon a failure identifying the switch, the channel, and the failed link.
Channels are configured using the standard CLI or Simple Network Management Protocol (SNMP).
Table 6-2 shows the Fast EtherChannel and Gigabit EtherChannel default configuration.
| Feature | Default Value |
|---|---|
Fast EtherChannel | Disabled on all Fast Ethernet ports (auto mode) |
Gigabit EtherChannel | Disabled on all Gigabit Ethernet ports (auto mode) |
EtherChannel support is hardware-dependent. To determine whether your hardware supports EtherChannel, see the documentation for your hardware or use the show port capabilities command.
These sections describe restrictions that apply and guidelines to follow when configuring Fast or Gigabit EtherChannel:
If improperly configured, some Fast EtherChannel or Gigabit EtherChannel ports are disabled automatically to avoid network loops and other problems. Use the following guidelines to avoid configuration problems:
On all Fast EtherChannel-capable hardware, port groups determine which ports can form a channel. Channels must be composed of contiguous ports from the same port group. A channel cannot have some ports from one group and some ports from another. However, you can configure multiple channels within a single group.
Use the show port capabilities command to determine the port groups on your hardware. On modules with two EtherChannel-capable ports, the ports form one group of two ports. On modules with four or more ports, the ports form one or more four-port groups.
On modules with two channel-capable ports, the group of two ports can be channeled in any of the following ways:
On modules with four or more channel-capable ports, each group of four ports can be channeled in any of the following ways:
Figure 6-1 shows valid and invalid Fast EtherChannel configurations (assuming at least two four-port port groups).
On all Gigabit EtherChannel-capable hardware, port groups determine which ports can form a channel. Channels must be composed of contiguous ports from the same port group. A channel cannot have some ports from one group and some ports from another. However, you can configure multiple channels within a single group.
Use the show port capabilities command to determine the port groups on your hardware. On modules with two EtherChannel-capable ports, the ports form one group of two ports. On modules with four or more ports, the ports form one or more four-port groups.
On these modules, the ports are grouped as follows:
On modules with two channel-capable ports, the group of two ports can be channeled in any of the following ways:
On modules with four or more channel-capable ports, each group of four ports can be channeled in any of the following ways:
These sections describe how to configure an EtherChannel bundle:
To configure a Fast EtherChannel or Gigabit EtherChannel bundle, perform this task in privileged mode:
| Task | Command |
|---|---|
Step 1 If you are unsure which ports you can channel 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 Make sure that the ports you want to channel are configured correctly. (Refer to the "EtherChannel Configuration Guidelines and Restrictions" section.) |
|
Step 3 Create a channel on the desired ports. | set port channel mod_num/ports {on | off | auto | desirable} |
Step 4 Verify the channeling configuration. | show port channel [mod_num[/port_num]] [info | statistics] |
This example shows how to create a two-port Fast EtherChannel bundle and verify the configuration:
Console> (enable) set port channel 1/1-2 on
Port(s) 1/1-2 channel mode set to on.
Console> (enable) 06/30/1998,17:09:32:PAGP-5:Port 1/1 left bridge port 1/1.
06/30/1998,17:09:32:PAGP-5:Port 1/2 left bridge port 1/2.
06/30/1998,17:09:33:PAGP-5:Port 1/1 joined bridge port 1/1-2.
06/30/1998,17:09:33:PAGP-5:Port 1/2 joined bridge port 1/1-2.
Console> (enable) show port channel
Port Status Channel Channel Neighbor Neighbor
mode status device port
----- ---------- --------- ----------- ------------------------- ----------
1/1 connected on channel WS-C2926 007475320 1/1
1/2 connected on channel WS-C2926 007475320 1/2
----- ---------- --------- ----------- ------------------------- ----------
Console> (enable)
To return a Fast EtherChannel or Gigabit EtherChannel bundle to its default configuration, perform this task in privileged mode:
| Task | Command |
|---|---|
Step 1 Return a channel to its default configuration (you must perform this task on both sides of the channel). | set port channel port_list auto |
Step 2 Verify the configuration. | show port channel [mod_num[/port_num]] [info | statistics] |
This example shows how to return a channel to its default configuration and how to verify the configuration:
Console> (enable) set port channel 1/1-2 auto Port(s) 1/1-2 channel mode set to auto. Console> (enable) show port channel No ports channelling Console> (enable)
Posted: Tue Mar 30 15:57:35 PST 1999
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