Catalyst 4500 Load balancing

Answered Question
May 7th, 2009

Hello.I Have two cisco catalyst 4500 (4507 R to be more specific) switches and there end all my connections from my racks. Each rack has a switch and from it i want to make an ether channel with two ports to each of my 4500 switches and load balance/failover the traffic i will get. Wich is the best method to do so?

I have this problem too.
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Correct Answer by Jon Marshall about 7 years 7 months ago

The 2960G is not a L3 switch. If it was you could run L3 etherchannels from the 2960 switches to the 4500 switches and use equal cost load balancing.

However you can't do this because your switches are L2 only.

If your 4500 switches are connected to each other via a L3 link then you could use both uplinks from a 2960 to each 4500 to send traffic from the servers and both uplinks would be used. GLBP would be good to use on the 4500 for the server vlans redundant gateways.

If the 4500 switches are connected via a L2 trunk then your options are more limited. If the servers are all in one vlan then one of the uplinks will probably block due to STP. If you have multiple server vlans then you could set the STP root for one vlan to be one 4500 and STP root for another of the vlans to be the other 4500. In this scenario HSRP would serve you just as well for redundant gateway.

Jon

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Joseph W. Doherty Thu, 05/07/2009 - 03:08

Load balance to/from the dual 4500 and/or etherchannel load balancing?

Is the rack switch L2 or L3? Model?

tkatsiaounis Thu, 05/07/2009 - 03:27

The racks are 2960 G so they are L3. Each rack has a 2960 switch and 4 cables going to the "networking room" i wanted to put two cables for each 4500 switch and combine those two to an ether channel. I wanted to load balance the two 4500 switches traffic from the servers to the outside world basically.

Joseph W. Doherty Thu, 05/07/2009 - 03:59

Believe 2960 series is only L2.

Sorry, still not clear. I assume servers are in the racks but you write "I wanted to load balance the two 4500 switches traffic from the servers to the outside world basically."

Load balancing issues comprise how both the 4500s and 2960s balance across the Etherchannels. How the 2960s balance across their two logical uplinks. How the dual 4500s balance to the 2960s and perhaps other devices.

tkatsiaounis Thu, 05/07/2009 - 14:17

Ok let me be more specific. I have 4 racks of servers each of them has a Catalyst 2960 G L3 switch. From each switch run a set of four cables to another room where the network equipement is located.There are the two catalyst 4500. What i want to do is the four cables divide them in two pairs and form an etherchannel from each pair to the catalyst 4500. Lets say pair1 -> switch 1 and pair 2 -> switch 2. I need to load balance the traffic coming from the servers to the outside world between the two 4500 catalyst switches. I hopew that i was more clear if you need any info please ask.

Correct Answer
Jon Marshall Thu, 05/07/2009 - 14:30

The 2960G is not a L3 switch. If it was you could run L3 etherchannels from the 2960 switches to the 4500 switches and use equal cost load balancing.

However you can't do this because your switches are L2 only.

If your 4500 switches are connected to each other via a L3 link then you could use both uplinks from a 2960 to each 4500 to send traffic from the servers and both uplinks would be used. GLBP would be good to use on the 4500 for the server vlans redundant gateways.

If the 4500 switches are connected via a L2 trunk then your options are more limited. If the servers are all in one vlan then one of the uplinks will probably block due to STP. If you have multiple server vlans then you could set the STP root for one vlan to be one 4500 and STP root for another of the vlans to be the other 4500. In this scenario HSRP would serve you just as well for redundant gateway.

Jon

Joseph W. Doherty Mon, 05/11/2009 - 16:50

To expand upon the information Jon provided. Remember to also change, if possible, the Etherchannel hash algorithm to obtain good distribution.

Another approach to the STP issue, if you have an intentional loop, adjust STP costs to not block the 2960 to 4500 links. Then you can use both logical uplinks within the same subnet, either with GLBP (or mHRSP).

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