EtherChannel PAgP and LACP modes
EtherChannel is a port link aggregation technology developed by Cisco, which provides fault-tolerant high-speed links between Switches, Routers, and Servers.
EtherChannel technology allows multiple physical Ethernet links (Fast EtherNet or Gigabit Ethernet) to combine into one logical channel.
There are two protocols used for negotiating EtherChannel and Link Aggregation. We can configure Etherchannel in three ways in Cisco Switches.
- Port Aggregation Protocol (PAgP) - Cisco Proprietary protocol
- IEEE Link Aggregation Protocol (LACP) - Industry Standard
- Manual Etherchannel Configuration - Without using any negotiation protocol listed above
Port Aggregation Protocol (PAgP) has two Channel modes and they are "Desirable" and "Auto".
Link Aggregation Control Protocol (LACP) has two Channel modes and they are "Active" and "Passive".
Port Aggregation Protocol (PAgP) Modes
Auto Mode: Auto mode in Port Aggregation Protocol (PAgP)) does not initiate the negotiation, but responds to Port Aggregation Protocol (PAgP) packets initiated by other end. Auto mode in Port Aggregation Protocol (PAgP) does not start Port Aggregation Protocol (PAgP) packet negotiation
Desirable mode: Desirable mode in Port Aggregation Protocol (PAgP) initiates the negotiation and tries to form EtherChannel with other end.
If you are using Port Aggregation Protocol (PAgP) for EtherChannel negotiation, EtherChannel will be formed only if two ends are configured under folowing modes.
| Desirable | Auto | |
| Desirable | Yes | Yes |
| Auto | Yes | No |
Link Aggregation Control Protocol (LACP)
Active Mode: Active Mode in Link Aggregation Control Protocol (LACP) initiates the negotiation and tries to form EtherChannel with other end.
Passive Mode: Passive Mode in Link Aggregation Control Protocol (LACP) does not initiate the negotiation, but responds to Link Aggregation Control Protocol (LACP) packets initiated by other end. Passive Mode in Link Aggregation Control Protocol (LACP) does not start Link Aggregation Control Protocol (LACP) packet negotiation.
| Active | Passive | |
| Active | Yes | Yes |
| Passive | Yes | No |
EtherChannel "on" mode
EtherChannel "on" mode makes the interface into an EtherChannel without any negotiation protocols like Port Aggregation Protocol (PAgP) or Link Aggregation Control Protocol (LACP). When using a EtherChannel "on" mode, EtherChannel will be created only when another interface group in EtherChannel "on" mode.
Switch interfaces exchange Port Aggregation Protocol (PAgP) packets only with partner interfaces configured in the auto or desirable modes. Switch interfaces exchange Link Aggregation Control Protocol (LACP) packets only with partner interfaces configured in the active or passive modes. Interfaces configured in the "on" Channel mode do not exchange Port Aggregation Protocol (PAgP) or Link Aggregation Control Protocol (LACP).
