Link Aggregation

Unanswered Question
Nov 26th, 2008

I have some question about Link Aggregation in regards to 3Com and Cisco.

I just bought a 3Com 4500 48 port switch (3CR17562-91) for an IDF.

I have a Cisco Catalyst 3750 and a Cisco Catalyst 3750-G in my server room.

3Com uses LACP (Link Aggregation Control Protocol) to take the 2 Gig ports and have them act as one 2Gb port (for faster data transfer and load balancing).

But does Cisco uses LACP? Or do they do their own thing with Ether Channel?

Will I be able to set the 3Com Link Aggregation up and then just plug the Cat6 cables into say port 2 and 3 and then do Ether Channel?

Or do I have to buy the adapters and plug the Cat6 cables into the 4 ports on the right side of the switch?

I have this problem too.
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John Blakley Wed, 11/26/2008 - 09:35

Cisco will use lacp. Depending on the 3Com (I know nothing about them), the link will come up. On the Cisco switch, you'll bundle whatever ports you want and then put them in an etherchannel:

int range g3/0/23-24

channel-group 1 mode active

channel-protocol lacp

This will put the two ports into a Po1 interface. (Port-channel 1)

That's your etherchannel port. If the negotiation doesn't come up, you can change the mode to passive or on, and it really depends on what the 3Com is doing on it's end as to how it'll negotiate.

You should be able to verify it has a bundled link by doing "sh etherchannel 1".



glen.grant Wed, 11/26/2008 - 09:40

LACP is the IEEE standard and is supported by all newer cisco switches . You can use any combination of ports on the 3750 as long as you configure them all the same . To verify channel use show etherchannel summary " .

on the cisco interfaces

int gx/x

channel-group 1 mode active

readymixed1 Wed, 11/26/2008 - 09:43

Here is what Cisco website says:

3750switchstackA(config)#interface range gigabitethernet 1/0/4 - 5

3750switchstackA(config-if-range)#channel-group 1 mode active

!--- This creates port channel 1 and configures it with LACP.

3750switchstackA(config-if-range)#switchport trunk encapsulation dot1q

3750switchstackA(config-if-range)#switchport mode trunk

3750switchstackA(config)#interface gigabitethernet 3/0/3

3750switchstackA(config-if)#channel-group 1 mode active

3750switchstackA(config-if)#switchport trunk encapsulation dot1q

3750switchstackA(config-if)#switchport mode trunk

Although John says to just do:

channel-group 1

channel-protocol lacp

Which way do i do it?

John Blakley Wed, 11/26/2008 - 09:47

"channel-group 1 mode active" creates the etherchannel. You want your etherchannel to be trunked. The channel-protocol isn't required, but it doesn't hurt either. (I compare it to the "deny ip any any" at the end of an ACL. You know it's there, but it's nice to see it.)

Active and Passive modes enable lacp.



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