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Cisco Catalyst Blade Switch 3130 for Dell Software Configuration Guide
OL-13270-01
Chapter37 Configuring EtherChannels and Link-State Tracking
Understanding EtherChannels
Use the silent mode when the switch is connected to a device that is not PAgP-capable and seldom, if
ever, sends packets. An example of a silent partner is a file server or a packet analyzer that is not
generating traffic. In this case, running PAgP on a physical port connected to a silent partner prevents
that switch port from ever becoming operational. However, the silent setting allows PAgP to operate, to
attach the port to a channel group, and to use the port for transmission.

PAgP Interaction with Other Features

The Dynamic Trunking Protocol (DTP) and the Cisco Discovery Protocol (CDP) send and receive
packets over the physical ports in the EtherChannel. Trunk ports send and receive PAgP protocol data
units (PDUs) on the lowest numbered VLAN.
In Layer 2 EtherChannels, the first port in the channel tha t c omes up provide s its MAC address t o the
EtherChannel. If this port is removed from the bundle, one of the remaining ports in the bundle pr ovides
its MAC address to the EtherChannel. For Layer 3 EtherChannels, the MAC address is a llocated by the
stack master as soon as the interface is created (through the inte rface port-channel global configuration
command).
PAgP sends and receives PAgP PDUs only from ports that are up and have PAgP enabled for the auto or
desirable mode.
Link Aggregation Control Protocol
The LACP is defined in IEEE 802.3ad and enables Cisco switches to manage Ethernet channels between
switches that conform to the IEEE 802.3ad protocol. LACP facilitates the automatic creation of
EtherChannels by exchanging LACP packets between Ethernet ports.
By using LACP, the switch or switch stack learns the identity of partners capable of supporting LACP
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 g roupe d bas ed on ha rd ware,
administrative, and port parameter constraints. For example, LACP 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, LACP adds the group to the spanning tree as a single swit ch po rt.

LACP Modes

Table37-2 shows the use r-configurab le Ethe rC han nel LACP modes fo r t he c hannel-group interface
configuration command.
Both the active and passive LACP modes enable ports to negotiate with partner ports to an
EtherChannel based on criteria such as port speed and, for Lay er 2 EtherChannels, trunking state and
VLAN numbers.
Table37-2 EtherChannel LACP Modes
Mode Description
active Places a port into an active negotiating state in which the port sta rts nego tiations with other
ports by sending LACP packets.
passive Places a port into a passive negotiating state in which the port responds to LACP packets
that it receives, but does not start LACP packet negotiation. This setting minimizes the
transmission of LACP packets.