Eather channel or Port Channel are names of Technology of using a group of ports as a single link to connect between Two switches, Switch - router, Or Switch and server the aim of it is High availability and increase link bandwidth.
There Three protocols of the port group:
1- PAGP(Port Aggregation Group Protocol) it is CISCO property protocol using up to 8 ports per group and there are 2 configuration modes ( Auto, Desirable), it's essential that both ends must be configured as PAGP EtherChannel
Auto Mode: Doesn't initiate the negotiation but responds to packets initiated by the other end ( note that the other end should be configured as desirable mode only if it configured as auto the channel group will no function).
Desirable Mode: Initiate the negotiation and tries to form EtherChannel with the other end regardless of the other end mode.
Summary of PAGP:
- Both ends PAGP configured
- It will act properly if both ends configured as ( Auto- Desirable, Desirable-Auto, Desirable-Desirable)
2- LACP ( Link Aggregation Control Protocol ) Open Standard protocol used to tie up to 8 ports and this protocol has Two Modes for configuration
- Active Mode: Initiate negotiation and tries to perform EtherChannel with the other end
- Passive Mode: Doesn't initiate the negotiation but responds to packets initiated by the other end.
Summary of LACP
It is the same as PAGP both ends must be configured as LACP and it will act properly unless both ends configured as Passive mod
3- On ( EtherChannel On) this mode considered as manual EtherChannel " ON" means no protocols are used no packets negotiations and initiations required also no modes needs to be configured ( active, passive, auto, desirable) to act well it just need to configure both ends as EtherChannel On.
The drawback of the EtherChannel On in case of using any layer one device like modem or media converter between any Etherchannel devices will not be able to detect and respond to link failure and keep sending traffic while PAGP/LACP will detect any failure and respond to it.
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