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EtherChannel Overview
EtherChannel is a Cisco technology that enables the aggregation or bundling of switchports into one logical link. Bundling multiple switchport ethernet links into one logical channel increases bandwidth as well creating redundancy and fault tolerance. For example, a bundle of four switchports into one EtherChannel would provide four times the bandwidth coming to and from the switch. EtherChannel bundles or port groups can be run from switch-to-switch or switch-to-server if the server’s network interfaces cards (NICs) support EtherChannel. You can bundle up to eight switchports in one Etherchannel port group with no more than six EtherChannel port groups per switch.
Background
Three switches have just been installed. There are redundant uplinks between the switches. Usually, only one of these links could be used; otherwise, a bridging loop might occur. However, using only one link utilizes only half of the available bandwidth. EtherChannel allows up to eight redundant links to be bundled together into one logical link. In this lab, you will configure Port Aggregation Protocol (PAgP), a Cisco EtherChannel protocol, and Link Aggregation Control Protocol (LACP), an IEEE 802.3ad open standard version of EtherChannel.
LACP vs PAgP
See First and most basic difference between LACP(Link Aggregation Control Protocol) and PAgP(Port Aggregation Protocol ) is , LACP is formed under IEEE 802.3ad standards and PAgP is CISCO-Proprietary .
LACP is used to dynamically build an EtherChannel. 2 Modes are available for this protocol :
1) ACTIVE MODE
In Active Mode ,the active end of group starts the process to create an EthernetChannel. If both ends are active Channel will be easily formed , NO BIG DEAL !
A port in the active mode can form an EtherChannel with another port that is in the active or passive mode.
2)PASSIVE MODE
In Passive Mode , process to form EthernetChannel is not commenced . It only responds to the initiator at other end. If both ends are passive , you can’t form Channel.
A port in the passive mode cannot form an EtherChannel with another port that is also in the passive mode because neither port starts LACP negotiation.
PAgp also has two similar modes namely , Desirable and Auto.
Desirable Mode is similar to Active Mode of LACP and Auto mode is similar to Passive mode.
One can have ports on standby using LACP not available with PAgP.
If you need form the etherchannel on stack switch, it is better to choose LACP since LACP support cross-stack Etherchannel. The PAgP doesn’t support cross-stack etherchannel on cisco375.
