Our new subject is : Etherchannel ! We are gonna talk about “what is etherchannel” , “how it works” and etc. First of all etherchannel is a great way to  make load balancing.

etherchannel

As you can see from the figure above, etherchannel combines the switch ports and works it like a one link. There are four 1 giga links between two switches. Etherchannel combines them to 4 giga but that is not a physical link surely, that’s a logical link. There are two protocols that helps you implementing etherchannel :

1- PAGP ( Port Agg Protocol )

– PAGP is a Cisco proprieraty protocol.

– Port modes of PAGP are AUTO , DISERABLE and ON ( Best path ) .

2- LACP ( Link Agg Protocol )

– LACP is not a Cisco proprieraty protocol, it is an industry standart. ( 802.3AD )

– Port modes of  LACP are PASSIVE , ACTIVE and ON

There are two  types of etherchannel :

1- LAYER – 2 ETHERCHANNEL

Layer – 2 etherchannel is used on Layer -2 switches like Cisco 2960 etc.

CONFIGURING LAYER – 2 ETHERCHANNEL

layer 2 etherchannel

SWITCH_A(conf)#interface range Fa0/23 - 24
SWITCH_A(conf-if)#channel protocol pagp
SWITCH_A(conf-if)#channel group 1 mode desirable

 

*** Same commands are implemented on SW B too. But just channel group mode is made “auto” to make a match between auto and desirable.

Configuration is verified with these commands :

SWITCH_A#show ip interface brief
SWITCH_A#show etherchannel detail


2- LAYER – 3 ETHERCHANNEL


Layer – 3 etherchannel is used on Layer -3 switches like Cisco 3750 etc.


Trick : It is enough that just one switch is Layer -3.


CONFIGURING LAYER – 3 ETHERCHANNEL


layer 3 etherchannel


SWITCH_A(conf)#interface port-channel 1
SWITCH_A(conf-if)#no switchport
SWITCH_A(conf)#ip address 10.1.1.1 255.255.255.0
exit
SWITCH_A(conf)#interface range Fa0/23 - 24
SWITCH_A(conf-if)#no switchport
SWITCH_A(conf-if)#channel group 1 mode desirable




    

  • Same configs are made for the other switch too. 
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  • All ports should be on the same speed and duplex mode. 
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  • Ports that are using for etherchannel should be in same VLAN or configured trunk.
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  • If you make a change in port-channel, that effects all the ports connected to it !
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