how to configure link redundancy

Unanswered Question
Aug 14th, 2008


we currently have 1 x 10Gb link connecting 2 data centres. We will be deploying the second 10Gb link. How do we configure the switch to enable the new 10Gb to carry all traffic while the first 10Gb will only be used if the new 10Gb link fails.

Any help is much appreciated.



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Marwan ALshawi Thu, 08/14/2008 - 15:54

if u r connecting switch to switch and u use L2 links u can do it through spaning-tree

husycisco Thu, 08/14/2008 - 15:56

Hello Poh-Fun

This will form automatically according to your spanning tree configuration between switches. But I suggest not to make a 10Gb link wait and stay unutilized untill the primary goes down. Implement etherchannel instead. You will have redundancy as well as improved bandwidth (2x 10 Gb).


pokwan Thu, 08/14/2008 - 16:27


Thanks very much for the reply. We just wanted to test the new 10Gb for a week before having both the 10GB live. I understand that which link will be used is depending on the spanning-tree configuration.

Having just 1 10Gb active is just temporary for a week. Can you please advice how it can be achieved?



husycisco Thu, 08/14/2008 - 16:48


If both switches are Cisco, STP (Spanning tree) is enabled by default. And if two switches connected each other with two uplinks, one will automatically be set to blocking state by the nature of STP. If the fowarding one fails, blocking port will change its state to forwarding within 50 seconds. So you dont need special configuration.

One thing to keep in mind, If these datacenters do have their own STP instances locally, introducing other datacenter into this L2 network may extend the STP tree in an undesired way. So double-check your STP planning


pokwan Thu, 08/14/2008 - 17:13


How do we ensure that the new 10Gb will be the one utilized and not the first 10Gb (only active when the new link fails). Both the link are connected to the same (to the same switches).

I have enslosed a visio diagram of the connections.

The links in red are the current (first) 10Gb. The ones in black are to deploy and we only want traffic traversing the black links only unless it fails then it fails over the those in red.




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