Port Aggregation Protocol - Cisco Catalyst 2960 Software Configuration Manual

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Configuring EtherChannels and Link-State Tracking

After you configure an EtherChannel, configuration changes applied to the port-channel interface apply

to all the physical ports assigned to the port-channel interface. Configuration changes applied to the

physical port affect only the port where you apply the configuration. To change the parameters of all

ports in an EtherChannel, apply configuration commands to the port-channel interface, for example,

spanning-tree commands or commands to configure a Layer 2 EtherChannel as a trunk.

Port Aggregation Protocol

The Port Aggregation Protocol (PAgP) is a Cisco-proprietary protocol that can be run only on Cisco

switches and on those switches licensed by vendors to support PAgP. PAgP facilitates the automatic

creation of EtherChannels by exchanging PAgP packets between Ethernet ports.

By using PAgP, the switch learns the identity of partners capable of supporting PAgP and the capabilities

of each port. It then dynamically groups similarly configured ports into a single logical link (channel or

aggregate port). Similarly configured ports are grouped based on hardware, administrative, and port

parameter constraints. For example, PAgP groups the ports with the same speed, duplex mode, native

VLAN, VLAN range, and trunking status and type. After grouping the links into an EtherChannel, PAgP

adds the group to the spanning tree as a single switch port.

You can use PAgP only in single-switch EtherChannel configurations; PAgP cannot be enabled on

cross-stack EtherChannels. PAgP dynamically groups similarly configured ports on a single switch in

the stack into a single logical link. For more information, see the

Guidelines" section on page

Relationship of Physical Ports, Logical Port Channels, and Channel Groups

port-channel

Channel-group

Catalyst 2960 and 2960-S Switches Software Configuration Guide, Release 15.0(1)SE

Physical ports

"EtherChannel Configuration

Understanding EtherChannels

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