What is Etherchannel or Link Aggregation?

What is Etherchannel or Link Aggregation?

If there is more the one wired connection in between two Switches to get more bandwidth, normally there is only one wired connection is active and the other links are kept blocked by the Switch to avoid looping in between two Switches.


So Etherchannel or Link Aggregation is the feature to use logically all the wired links as one single link.

There are some conditions on using Etherchannel or Link Aggregation.
All the links needs to be connected in same type of interface, they needs to be same Duplex mode(Half or Ful Duplex) and all the interface ports needs to be in same speed.

There are two types of Etherchannel:
1. PAGP(Cisco Propitiatory): Port Aggregation Protocol
2. LACP: Link Aggregation Control Porotocol

PAGP has 3 modes. a) Desirable, b) Auto & c) On
LACP has 2 modes. a) Active & b) Passive

Auto/Passive: Doesn't negotiate by itself. If any-others offered to form Etherchannel then It'll agree to do so.
Desirable/Active: It does negotiate to others forming Etherchannel.
On: It forms Etherchannel without negotiating to others.

In 2964 Switch or Layer 3 Switch, 8links can be connected together and can be created at best 6 Etherchannel.

Etherchannel can be formed by follows:

On -------------------------------------On

Desirable ----------------------------- Auto

Active ---------------------------------Active

Desirable ------------------------- Desirable