Configuration - Cisco Catalyst 2000 Configuration Handbook

■ If a link within an EtherChannel fails, the traffic that normally crosses the failed link
is moved to the remaining links.
EtherChannel links can be static access ports or trunk ports. However, all links to be
■
bundled must have consistent configurations before an EtherChannel can form.
Note PAgP sends frames to destination address 01:00:0C:CC:CC:CC, as an 802.2
Subnetwork Access Protocol (SNAP) protocol 0x000C0104. LACP sends frames to desti-
nation address 01-80-c2-00-00-02 using protocol 0x8809.

Configuration

(Optional) Select an EtherChannel protocol under the physical interface you are as-
1.
signing to the port-channel:
channel-protocol {pagp | lacp}
By default, each module uses the PAgP protocol (pagp) for dynamic EtherChannel
control.
Tip PAgP and LACP are not interoperable. Therefore, use the same protocol on the mod-
ules and ports at both ends of a potential EtherChannel.
(Optional) Adjust the STP costs for an EtherChannel.
2.
a. Set the STP port cost:
interface [mod[/port]]
spanning-tree cost cost
By default, the STP port cost for an EtherChannel is based on the port cost of
the aggregate bandwidth. For example, a single 100 mbps port has a port cost of
19. When two 100 mbps ports are bundled as an FEC, the port cost for 200
mbps is 12. A bundle of four 100 mbps ports gives a port cost of 8 for the 400
mbps bandwidth. Refer to Table 7-1 in Chapter 7, "Spanning Tree Protocol (STP),"
for STP port cost values.
You can change the port cost for all EtherChannels by using the all keyword or a
single EtherChannel by giving its channel-id number. To find this index, use the
show channel group (PAgP) or show lacp-channel group (LACP) command. The
channel-id is a unique number that is automatically assigned to the
EtherChannel.
The STP port cost is given as cost (1-65535 in 16-bit "short mode" or 1-
4294967296 in 32-bit "long mode"). Refer to section "7-1: STP Operation," in
Chapter 7 for more cost information.
Chapter 4: Layer 2 Interface Configuration 63