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Cisco Catalyst Blade Switch 3130 for Dell Software Configuration Guide
OL-13270-01
Chapter37 Configuring EtherChann els and Link-State Tracking Understanding EtherChannels
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. You can use PAgP only
in single-switch EtherChannel configurations; PAgP cannot be enabled on cross-stack EtherCh anne ls.
For more information, see the “EtherChannel Configuration Guidelines” section on page 37-11.
By using PAgP, the switc h or switch stack learns the identity of partn ers capabl e of supporting PAgP and
the capabilities of each port. It then dynamically groups similarly configured ports (on a single switch
in the stack) into a single logical link (channel or aggregate port). Similarly c onfigured 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 a s a sin gle sw it ch
port.

PAgP Modes

Table37-1 shows the use r-configurab le Et herC ha nnel PAgP modes for the channel-group interface
configuration command.
Switch ports exchange PAgP packets only with partner ports configured in the auto or desirable modes.
Ports configured in the on mode do not exchange PAgP packets.
Both the auto and desirable modes enable ports to negotiate with partner ports to form an EtherChannel
based on criteria such as port speed and, for Layer 2 EtherChannels, trunking state and VLAN numbers.
Ports can form an EtherChannel when they are in different PAgP modes as long as the modes are
compatible. For example:
•A port in the desirable mode can form an E therCh annel w ith ano ther po rt that i s in the desirable or
auto mode.
•A port in the auto mode can form an EtherChannel with another port in the desirable mo de.
A port in the auto mode cannot form an EtherChannel with another port that is also in the auto mode
because neither port starts PAgP negotiation.
If your switch is connected to a partner that is PAgP-capable, you can configure the swit ch po rt for
nonsilent operation by using the non-silent keyword. If you do not specify non-silent with the auto or
desirable mode, silent mode is assumed.
Table37-1 EtherChannel PAgP Modes
Mode Description
auto Places a port into a passive negotiating state, in which the port responds to PAgP packets
it receives but does not start PAgP packet negotiation. This setting minimizes the
transmission of PAgP packets. This mode is not supported when the EtherChannel
members are from different switches in the switch stack (cross-stack EtherChannel).
desirable Places a port into an active negotiating state, in which the port starts negotiations with other
ports by sending PAgP packets. This mode is not supported when the EtherChannel
members are from different switches in the switch stack (cross-stack EtherChannel).