What are the link aggregation protocols in Cisco Switches, what are their modes required to bundle a link?

Dynamic Configuration

Cisco switches support two dynamic aggregation protocols:

  • PAgP (Port Aggregation Protocol) – Cisco proprietary aggregating protocol.
  • LACP (Link Aggregation Control Protocol) – IEEE standardized aggregation protocol, originally defined in 802.3ad.

PAgP and LACP are not compatible – both sides of an Etherchannel must use the same aggregation protocol.
EthernChannel – PAgP
It supports 2 Modes

  • Desirable – actively attempts to form a channel
  • Auto – waits for the remote switch to initiate the channelA PAgP channel will form
  • desirable <- -> desirable
  • desirable <- -> auto#interface range f0/22 – 24 #channel-protocol pagp #channel-group 1 mode desirable / auto

    EtherChannel – LACP It has 2 Modes

  • Active – actively attempts to form a channel
  • Passive – waits for the remote switch to initiate the channelAn LACP channel will form
  • active <- -> active
  • active <- -> passive#interface range f0/22 – 24 #channel-protocol lacp
    #channel-group 1 mode active / passive

    Maximum of 8 active ports are supported in a single Etherchannel. LACP supports adding an additional 8 ports into the bundle in a standby state, to replace an active port if it goes down.

  • LACP assigns a numerical port-priority to each port, to determine which ports become active in the Etherchannel. By default, the priority is set to 32768, and a lower priority is preferred. If there is a tie in system-priority, the lowest switch MAC address is preferred.#interface range f0/22 – 24 #lacp port-priority 100

#lacp system-priority 500

#show etherchannel summary #show port-channel summary