Etherchannel is comprised of multiple physical links that are bundled in logical links. It helps to increase the bandwidth of LAN ports to be compatible with high-speed WAN port. Physical links must share the similar characteristics in order to aggregate such as duplex mode, Same Vlan, similar speed, Native and allowed Vlan, STP Setting, Trunking Encapsulations (ISL or 802.1Q) etc. The number of links supported per bundle is bound by the platform. There are two protocols Port Aggregation Protocol (PAgP - Cisco Proprietary) and Link Aggregation Control Protocol (LACP - IEEE 802.3ad) PAgP enables automatic Etherchannel Creation and by default, PAgP packets are sent between Ether channel-Capable ports. Ling aggregation include Ethernet Channel, Gig Channel, or 10 Gig Channel.
Configuration is very simple as we have to only assign the interface range to a channel-group with Single line command. The group no is locally significant and can be different on both sides. The various mode available in the highlighted commands shown in the Packet Tracer Snap.
Switch(config)#int range fa0/1 - 3
Switch(config-if-range)#channel-group 1 ?
mode Etherchannel Mode of the interface
Switch(config-if-range)#channel-group 1 mode ?
active Enable LACP unconditionally
auto Enable PAgP only if a PAgP device is detected
desirable Enable PAgP unconditionally
on Enable Etherchannel only
passive Enable LACP only if a LACP device is detected
Run channel-group command on both i.e. here Sw2 & Sw3. The picture above depicts all the ports in a green signal which means one single Etherchannel is running. If you hit show spanning-tree, Po1 in root forwarding can be seen.
Configuration is very simple as we have to only assign the interface range to a channel-group with Single line command. The group no is locally significant and can be different on both sides. The various mode available in the highlighted commands shown in the Packet Tracer Snap.
Switch(config)#int range fa0/1 - 3
Switch(config-if-range)#channel-group 1 ?
mode Etherchannel Mode of the interface
Switch(config-if-range)#channel-group 1 mode ?
active Enable LACP unconditionally
auto Enable PAgP only if a PAgP device is detected
desirable Enable PAgP unconditionally
on Enable Etherchannel only
passive Enable LACP only if a LACP device is detected
Run channel-group command on both i.e. here Sw2 & Sw3. The picture above depicts all the ports in a green signal which means one single Etherchannel is running. If you hit show spanning-tree, Po1 in root forwarding can be seen.
Auto, Desirable are PAgP mode and Active, Passive are LACP enabled mode. Both modes of each Protocol have the same meaning as Auto/Passive enabled with PAgP/LACP forms an Etherchannel only if same protocol is detected. i.e. PAgP Auto/LACP Passive mode only negotiates if it receives PAgP/LACP packets and will be in listening state. Port with PAgP Desirable/LACP Active mode initiates the negotiation with other switch running PAgP/LACP port.
The 'On' mode is about forming the channel link without protocol. So if you put 'On' mode both sides of the Channel Etherchannel is created.This mode sometimes incorrectly referenced to PAgP mode. It doesn't necessarily need a protocol to form a channel. So if ever you asked the question which protocol is active in the 'On' mode of Etherchannel the answer is none.
When it comes to remember the negotiation table, i have a good idea. Follow some basic.
ON+ON = ON
Auto+Auto=Down
Passive+Passive=Down
As you know both Auto & Passive has same meaning.
Desirable+Desirable=ON
Active+Active=ON
And if any combination comprised one of the above, it will be 'ON' Such As
Desirable+Auto=ON
Active+Passive=ON
All the rest combination will result in DOWN state.
Some show commands
show etherchannel summary
Show etherchannel protocol
show etherchannel detail
Show spanning tree active
I Hope I made this clear enough.
Please comment for Suggestions, Questions.
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