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Etherchannel Configuration Question

dhopper82
Level 1
Level 1

Is there a good document on setting up Port Channels??  Specfically is there a way to optimize them so I know that they are capable of pushing traffic on more than one interface if the traffic exceeds its capability???

We have a backup device that is setup on a 4 port (all 4 ports are set to gig speed) etherchannel.  When the device sends out traffic it maxes out one link and one link only and sends no traffic on the rest of the ports.  I am trying to verify that this is not a switch issue.

The port configuration on the channel group is mode active.

channel-group 17 mode active interface GigabitEthernet10/8
description HO-NB5 Backup
switchport
switchport access vlan 213
no ip address
speed 1000
duplex full
spanning-tree portfast
channel-group 17 mode active

1 Reply 1

Jon Marshall
Hall of Fame
Hall of Fame

It's important to understand how etherchannel uses the links ie.

backup server = s1

s2 and  s3 are devices the backup server sends traffic to.

If the backup server sends 950Mbps to s2 and 950Mbps then providing you are using the right load-balancing method there is a good change 2 of the 4 links will be used, one for each communication.

But if the backup server sends 1.5Gbps to s2 then it will not use 2 links for this. It will only use one link and you will get an oversubscribed link. Etherchannel will not solve this problem for you. This is because etherchannel always sends the same src/dst pair on the same link.

What this src/dst pair are depends on your switch. It can mac-address/IP address/L4 port information.

See this doc for full details of how etherchannel load-balancing works -

http://www.cisco.com/en/US/tech/tk389/tk213/technologies_tech_note09186a0080094714.shtml

Jon