SLB type scenario

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Dec 18th, 2007
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I have a very restricted situation where I need two physical servers to be presented on the network as one virtual IP address.

I cannot make any changes to the servers, i.e. Cluster or NLB so that option is out.

I was looking at the SLB option but this isn't supported on 4500's. I also do not have the option of additional blades or equipment so just the command syntax of the switch is my option.

Essentially I'm looking at a command syntax on a 4500 to translate requests to a specific IP and present them to the servers behind.

For. e.g.

The physical IP's are:



I would like to use all the time and have the network translate the request to either of the two physical IP's of the servers. I don't want any additional functionality of load balancing, just a translation to one server and if that isn't a available then the request goes to the second.

I'm wondering if NAT can translate to one IP and if this isn't available then the 2nd.

I hope this makes some sense. Any help is appreciated.



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Jon Marshall Wed, 12/19/2007 - 07:39
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Hi Wayne

Unfortunately the 4500 does not support NAT either, for that you need a 6500 believe it or not.

I'm not sure there is anything on the 4500 that will meet your requirement. The only thing i can think of is DNS round-robin which is nothing to do with the switch.

In your DNS you have 2 entries for the same server name ie.

"virtual name of service"

"virtual name of service"

The DNS server will then return the first time it is asked for the virtual service name and when it is asked the second time. Obviously DNS has no idea if one of the servers goes down so you would get timeouts if one went down.

Obviously this isn;t presenting a VIP but rather a DNS name resolving to 2 different IP addresses.


wrgoulden Thu, 12/20/2007 - 02:02
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Thanks Jon for your response.

I will look into the DNS approach.




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