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Link aggregation to 2 core switches

Hi guys,

We're planning to purchase 2 x WS-C3750G-12S-E core switches and a WS-C2960G-48TC-L access switches.

I'd like to know, is it possible to uplink a fiber link from the WS-C2960G-48TC-L to each of the core switches. Which means, there will be a fiber link from WS-C2960G-48TC-L to the first core and fiber link from WS-C2960G-48TC-L to the second core.

We're planning to aggregate both links to double-up the throughput from the access switch to the cores. Is this possible? If it is, how do i configure it? What is this technology known as in Cisco?

Thank you.

1 ACCEPTED SOLUTION

Accepted Solutions
Purple

Re: Link aggregation to 2 core switches

Your design should work fine . I have a little different view here , Two different takes here , you can use cross stack etherchannel as some have suggested which if you lose one of the links the uplink is downgraded to a single link , or you could put the etherchannel on a single switch in which case if the switch actually goes down it will fall over to the other side which will have the full 2 gig uplink bandwidth . This doesn't help in the scenario where you lose one of the links in the uplink , in that case you will still have a degraded uplink .So you can use cross stack in which case if one of the 3750 switches goes down you will continue to work but on a degraded uplink or you can put the etherchannel on one switch of 3750 stack in which case if the switch where the uplinks are fails it will fall over to the backup which is what it is for and they will have access to the full 2 gig uplink bandwidth to the backup. Also I would make sure the etherchannels are "trunked" etherchannels as I am sure at some point you will want to run more than 1 vlan down those uplinks . Hopefully this isn't too confusing ...

7 REPLIES

Re: Link aggregation to 2 core switches

yes, it is possible to connect fiber link from WS-C2960G-48TC-L to the first core and fiber link from WS-C2960G-48TC-L to the second core.

Etherchanel is the technology used in cisco to aggregate links in a single bundle.

But etherchannel can be built on ports on two same devices which means you can configure etherchannel on 2-8 ports on cisco 2960 with first core and another etherchannel can be configured on cisco 2960 and second core.

check this URL to get more information.

http://www.cisco.com/en/US/products/hw/switches/ps5023/products_configuration_guide_chapter09186a00801cdea1.html

HTH, rate if it does ....

Re: Link aggregation to 2 core switches

How is your core connected.

Heres what i will do

Since your core is a 3750, i would stack them on the backplane.

Connect the fiber from the 2960's such that one fiber terminates physically on one switch and the other on the 2nd switch

This way you will get backplane throughput between the core and your 2960 have redundancy as well as uplink aggregation

HTH, rate if it does

Narayan

New Member

Re: Link aggregation to 2 core switches

I just got some new info. Actually, we might be getting 2 x WS-C3750G-12S-E and 2 x WS-C3750G-24TS-E. Please take a look at the attachment for the design diagram. Can the WS-C2960G-48TC-L be used in this situation? Will cross-stack etherchannel configuration work?

Thanks.

Re: Link aggregation to 2 core switches

It will work

When you stack the switches, they become one logical switch managed by a single IP address.

The ports on the 2nd switch would be just seen as 2/0/1 and third switch would be 3/0/1 & so on...

The 3750 is the only switch which provides Cross stack etherchannel because of its unique stackwise technology

HTH, rate if it does

Narayan

New Member

Re: Link aggregation to 2 core switches

If you look at the diagram, it shows two different stacks. And the C2960G is connected to both of the stacks. Can I use the C2960G to connect to two different stacks?

Both stacks are connected using Cat6 cables.

Re: Link aggregation to 2 core switches

Hi Saravanan,

i was not clear with ur question, but will make you clear with the options.

Option A(Recommended)

with the diagram u can have HSRP configured, so that even if link or entire stack fails, the other will take care,

Option B

you can go head with the diagram you hav specified.

Option C

you can even connect 2 links on a 1 side stack, each link to each swtich, in that case etherchannel has to be configured.

hope ur clear

rate this post if cleared.

Purple

Re: Link aggregation to 2 core switches

Your design should work fine . I have a little different view here , Two different takes here , you can use cross stack etherchannel as some have suggested which if you lose one of the links the uplink is downgraded to a single link , or you could put the etherchannel on a single switch in which case if the switch actually goes down it will fall over to the other side which will have the full 2 gig uplink bandwidth . This doesn't help in the scenario where you lose one of the links in the uplink , in that case you will still have a degraded uplink .So you can use cross stack in which case if one of the 3750 switches goes down you will continue to work but on a degraded uplink or you can put the etherchannel on one switch of 3750 stack in which case if the switch where the uplinks are fails it will fall over to the backup which is what it is for and they will have access to the full 2 gig uplink bandwidth to the backup. Also I would make sure the etherchannels are "trunked" etherchannels as I am sure at some point you will want to run more than 1 vlan down those uplinks . Hopefully this isn't too confusing ...

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