Loadbalancing between Servers using 4500 switch

Unanswered Question
Dec 26th, 2008

Hi All,

I have CISCO 4507R switch. It is working perfectly.

I have two Linux Server configured as web servers with IP address and The intention is to provide Load Balancing / High Availability in the servers. We have not configured clustering or Network Load Balancing (NLB) between servers as it does not support active / active clustering.

Servers are connected in the following ports

Giga 0/1 - SERVER 1

Giga 0/2 - SERVER 2

So I am trying to configure the load balancing in the switch, so that both the servers should the receiving the traffic from clients.

Is there any way I can configure Virtual IP address in the switch for this web servers, so that this Virtual IP address will be given to clients for communicating with the servers.

Or otherwise any workaround or solution is there to achieve my requirement.

I read that Etherchannel is not possible between One switch and two different servers. Is that true?


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Jon Marshall Fri, 12/26/2008 - 02:38


IOS does have a feaure called SLB (Server Load Balancing) but unfortunately it is not supported on the 4500 series switch (it is on the 6500).

You are right that etherchannel is not a solution for you here.

One possible solution is "poor mans" load-balancing using DNS where you have 2 entries for the same URL and eg.

http://www.site.com ->

http://www.site.com ->

the DNS server will respond in a round robin fashion returning the .100 the first time a request for www.site.com is requested and .200 the next time.

There is a big drawback to this solution though. If one of the servers goes down DNS does not know it has gone down so it will still return the IP address. And if a client has cached it's DNS response and then the server goes down the client will continue to use that IP address until it times out of it's cache.


hclisschennai Fri, 12/26/2008 - 04:38

Hi Jon,

Thanks for your response and initivatives.

Can you please explain how to do Server Load Balancing in 6500 Series switch. So that i will use 6500 Switch in this case.

Also RRDNS is not the solution as you mentioned.

Please suggest me how to achieve this. I am also attaching the network diagram for your reference.

Jon Marshall Fri, 12/26/2008 - 06:19

Attached is a link to configuring IOS SLB on the 6500. However one of the key restrictions is that the client(s) and server(s) cannot be on the same subnet/vlan so you would need to do some readdressing of your clients if you wanted to use SLB on the 6500 -


There are of course other options ie. there are standalone load-balancers and an ACE module that can be inserted into the 6500 chassis. With these devices you can have the clients and servers on the same IP subnet. But obviously these would entail additional hardware costs.



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