for the Cisco Catalyst 6500 is IP. EtherChannel bundles individual Ethernet links into a single logical link that provides bandwidth up to 1600 Mbps (Fast EtherChannel, full duplex) or 16 Gbps (Gigabit EtherChannel) between two Cisco Catalyst switches. All interfaces in each EtherChannel must be the same speed and duplex, and both ends of the channel must be configured as either a Layer 2 or Layer 3 interface.If a link within the EtherChannel bundle fails, traffic previously carried over the failed link is carried over the remaining links within the EtherChannel.The configuration applied to the individual physical interfaces that are to be aggregated by EtherChannel affects only those interfaces. Each EtherChannel has a logical port channel interface. A configuration applied to the port channel interface affects all physical interfaces assigned to that interface. (These can be STP commands or commands to configure a Layer 2 EtherChannel as a trunk.) EtherChannel provides the following features and benefits:

• Allows for the creation of a very high bandwidth logical link
• Load balances among the physical links involved
• Provides automatic failover
• Simplifies subsequent logical configuration (configuration is per logical link instead of per physical link)

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Content 3.4 Configuring Link Aggregation with EtherChannel 3.4.2 Describing PAgP and LACP Cisco’s proprietary Port Aggregation Protocol (PAgP) and the IEEE standard Link Aggregation Protocol (LACP) automatically create bundled Ethernet links. PAgP packets are sent between Fast EtherChannel-capable ports to negotiate the forming of a channel. When PAgP identifies matched Ethernet links, it groups the links into an EtherChannel. The EtherChannel is then added to the spanning tree as a single bridge port. PAgP manages EtherChannel. PAgP packets are sent every 30 seconds using multicast group MAC address 01-00-0C-CC-CC-CC with protocol value 0x0104. PAgP checks for configuration consistency and manages link additions and failures between two switches. It ensures that when an EtherChannel is created that all ports have the same type of configuration, because it is mandatory that all ports have the same speed, duplex setting, and VLAN information. Any port modification after the creation of the channel will also change all the other channel ports. The last component of EtherChannel is the creation of the logical port. The logical port, or Agport, is composed of all the ports that make up the EtherChannel. The Agport’s functionality and behavior are no different than any other port. For instance, the spanning tree algorithm treats Agport as a single port. LACP is part of an IEEE specification (802.3ad) that allows several physical ports to be bundled together to form a single logical channel. LACP allows a switch to negotiate an automatic bundle by sending LACP packets to the peer. It performs a similar function as PAgP with Cisco EtherChannel. Because LACP is an IEEE standard, it can be used to facilitate EtherChannels in mixed-switch environments. Interfaces can be set in any of several modes to control EtherChannel formation. Figure shows the settings for PAgP and LACP. The following parameters are used in configuring LACP:

• System priority: Each switch running LACP must have a system priority, which can be specified automatically or through the CLI. The switch uses the MAC address and the system priority to form the system ID.
• Port priority: Each port in the switch must have a port priority, which can be specified automatically or through the CLI. The port priority and the port number form the port identifier. The switch uses the port priority to decide which ports to put in standby mode when a hardware limitation prevents all compatible ports from aggregating.
• Administrative key: Each port in the switch must have an administrative key value, which can be specified automatically or through the CLI. The administrative key defines the ability of a port to aggregate with other ports, determined by the following:
  • The port’s physical characteristics, such as data rate, duplex capability, and point-to-point or shared medium
  • The configuration constraints that you establish

LACP attempts to configure the maximum number of compatible ports in a channel. In some instances, LACP is not able to aggregate all the ports that are compatible; for example, the remote system might have more restrictive hardware limitations. When this occurs, all the ports that cannot be actively included in the channel are put in hot standby state and used only if one of the channeled ports fails.

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Content 3.4 Configuring Link Aggregation with EtherChannel 3.4.3 Describing EtherChannel Configuration Commands The commands in Figures and are used to configure and verify EtherChannel.

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Content 3.4 Configuring Link Aggregation with EtherChannel 3.4.4 Configuring Port Channels Using EtherChannel Figure illustrates the configuration of Layer 2 EtherChannel. Figure shows the steps for configuring and verifying an EtherChannel interface. Figure illustrates the configuration of Layer 3 EtherChannel. Figure shows the steps for configuring and verifying a Layer 3 EtherChannel interface. Use the show running-config interface port-channel num command to display the configuration specific to the port channel. Use the show interfaces [interface] [num] etherchannel command to display information about the port channel and the specific EtherChannel interfaces. The following example demonstrates how to verify the configuration of a Layer 3 EtherChannel. Switch#show interfaces fastethernet 5/4 etherchannel

Port state = EC-Enbld Up In-Bndl Usr-Config
Channel group = 1 Mode = Desirable Gcchange = 0
Port-channel = Po1 GC = 0x00010001 Pseudo-port-channel = Po1
Port indx = 0 Load = 0x55

Flags: S - Device is sending Slow hello. C - Device is in Consistent state.
A - Device is in Auto mode. P - Device learns on physical port.
Timers: H - Hello timer is running. Q - Quit timer is running.
S - Switching timer is running. I - Interface timer is running.

Local information:
Hello Partner PAgP Learning Group
Port Flags State Timers Interval Count Priority Method Ifindex
Fa5/4 SC U6/S7 30s 1 128 Any 55

Partner's information:
Partner Partner Partner Partner Group
Port Name Device ID Port Age Flags Cap.
Fa5/4 JAB031301 0050.0f10.230c 2/45 1s SAC 2D

Age of the port in the current state: 00h:54m:52s The following two command outputs show how to verify the configuration of Fast Ethernet interface 5/6 for Layer 2 EtherChannel. Switch#show running-config interface fastethernet 5/6

Building configuration...
Current configuration:
!
interface FastEthernet5/6
switchport access vlan 10
switchport mode access
channel-group 2 mode desirable
end

Switch#show interfaces fastethernet 5/6 etherchannel
Port state = EC-Enbld Up In-Bndl Usr-Config
Channel group = 1 Mode = Desirable Gcchange = 0
Port-channel = Po1 GC = 0x00010001
Port indx = 0 Load = 0x55

Flags: S - Device is sending Slow hello. C - Device is in Consistent state.
A - Device is in Auto mode. P - Device learns on physical port.
Timers: H - Hello timer is running. Q - Quit timer is running.
S - Switching timer is running. I - Interface timer is running.

Local information:
Hello Partner PAgP Learning Group
Port Flags State Timers Interval Count Priority Method Ifindex
Fa5/6 SC U6/S7 30s 1 128 Any 56
Partner's information:

Partner Partner Partner Partner Group
Port Name Device ID Port Age Flags Cap.
Fa5/6 JAB031301 0050.0f10.230c 2/47 18s SAC 2F

Age of the port in the current state: 00h:10m:57s Use the show etherchannel command to display port-channel information