Pagp Interaction With Other Features; Link Aggregation Control Protocol; Lacp Modes - Cisco IE-4000 Software Configuration Manual

Configuring EtherChannels
Information About Configuring EtherChannels
ports.
When the link partner of the switch is a physical learner (such as a Catalyst 1900 series switch), we recommend that you
configure the switch as a physical-port learner by using the pagp learn-method physical-port interface configuration
command. Set the load-distribution method based on the source MAC address by using the port-channel load-balance
src-mac global configuration command. The switch then sends packets to the Catalyst 1900 switch using the same port
in the EtherChannel from which it learned the source address. Only use the pagp learn-method command in this
situation.
PAgP Interaction with Virtual Switches and Dual-Active Detection
A virtual switch can be two or more core switches connected by virtual switch links (VSLs) that carry control and data
traffic between them. One of the switches is in active mode. The others are in standby mode. For redundancy, remote
switches, are connected to the virtual switch by remote satellite links (RSLs).
If the VSL between two switches fails, one switch does not know the status of the other. Both switches could change to
the active mode, causing a dual-active situation in the network with duplicate configurations (including duplicate IP
addresses and bridge identifiers). The network might go down.
To prevent a dual-active situation, the core switches send PAgP protocol data units (PDUs) through the RSLs to the
remote switches. The PAgP PDUs identify the active switch, and the remote switches forward the PDUs to core switches
so that the core switches are in sync. If the active switch fails or resets, the standby switch takes over as the active switch.
If the VSL goes down, one core switch knows the status of the other and does not change state.

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 that comes up provides its MAC address to the EtherChannel. If
this port is removed from the bundle, one of the remaining ports in the bundle provides its MAC address to the
EtherChannel.
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 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 grouped based on hardware, 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 switch port.

LACP Modes

Table 2 shows the user-configurable EtherChannel LACP modes for the channel-group interface configuration
command.
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