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357
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STP choice for redundancy and load balancing

mmullen
Level 1
Level 1

I am in the process of designing a network with two 4506 switches in the core and a stack of 2950 switches in each of the 3 closets. All of the servers will be attached to the 4500 core switches with dual 1000BaseT Gigabit adapters for load balancing and redundancy. Each stack of 2950 switches will have a gigabit uplihk to each of the 4500 core switches. I would like to load balance across both of the uplinks from each closet and also provide the fastest possible recovery in the event of a link failure. What would be the recommended configuration for setting up Spanning Tree in this scenario?

3 Replies 3

rsissons
Level 5
Level 5

You cannot have duplicate paths for load balancing at layer 2 in a purely switched environment. The purpose of spanning tree is to establish one path for all traffic so be reestablishde if the topology changes. End devices cannot handle duplicate responses over multiple paths.The only exception to this is doing source route bridging in a token ring environment where the RIF field enables multiple paths to be concurrently active.

I should have mentioned that it won't be purely layer 2. The 4500 switches will both be providing layer 3 switching. The network will be segmented with VLANs and the L3 engine used to route between the VLANs. The L3 interfaces on the 4500s will be configured with HSRP, with one 4500 being the primary for odd VLANs and the other being the primary for even VLANs.

I would like to have traffic in the closets for the odd VLANs go across one uplink to one of the 4500's, and traffic for the even VLANs go across the uplink to the other 4500. I have been doing some reading on 802.1s and 802.1w and I was thinking that I could put the odd and even VLANs on separate Spanning Tree instances and then set the port priority on the Gigabit uplinks.

rderfus
Level 1
Level 1

You can setup redundancy, but STP will block multipe path so that bridge loops will not be established. At gigabit speeds going full duplex why do you need load balancing? That's a 2 gig uplink. Most LAN traffic won't exceed that channel bandwidth.

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