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Wednesday, April 13, 2011

Need help planning redundancy.

Qsolved Question: Here is our current design.

We have 2 routers to 2 different providers.Both routers goto Sw001. Sw001 is an enhanced ios switch with ospf and bgp. Below Sw001 are couple of 3560 PoE switches that has phones and pc's connected too them. These are not enhanced switches.

What we would like to do is place another (hot spare) Sw0011 with an enhanced ios. We plan to put this switch between Sw001 and the access switches.So, if Sw001 goes down, we can just simply move the cables from Sw001 to Sw011.

We also wanted to plug one of the providers to Sw011 (as well as Sw001). Additionally, we were planning on running a crossover between Sw001 and Sw011 so that we can access the hot spare via the MPLS provider and via Sw001 (crossover). What would be the optimal design to get the end results we are looking for?

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Qsolved Answer:

Are you doing the inter-vlan routing for the vlans on the 3560s on sw001 ?

If so you should not be having to swap cables around in case of failure if you buy a 2nd switch. What you do is -

1) connect sw001 to sw0011 with a L2 etherchannel trunk

2) run HSRP between the L3 vlan interfaces on sw001 and sw0011

3) connect the 3560 switches to both sw001 and sw0011.

4) If you have multiple vlans on the 3560 switches then you can load-balance your vlans by making sw001 STP root for odd numbered vlans and HSRP active for odd numbered vlans. sw0011 will be STP root for even numbered vlans and HSRP active for even vlans.

The above is a very common setup. If sw001 fails then it will automatically failover to sw0011 without you having to do anything. A variation on the above is to run GLBP on sw001 and sw0011 and have a L3 interconnect between sw001 and sw0011 but either way is better than what you have.

As for the routers, ideally you want to connect each router to both switches ie. sw001 and sw0011 because if sw001 fails then it takes down the router with it unless that router is also connected to sw011. But you may not have the spare router interfaces for that so if that is the case simply connect one router to sw001 and one to sw0011.

Actually, your servers should have connections to both switches with teaming, where one connection is active and one is in standby. If you can do this then everything should be automatic ie. no manual intervention at all

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