Simple load balancing question

Unanswered Question
Jun 6th, 2008

We have a PeopleSoft ERP installation with two web servers. Our networking department purchased a 3750e switch as we wanted to load balance the two web servers.

However, I don't think we are getting what we need from the current configuration.

Ideally, I want a "virtual" IP that is translated at the switch to either web server 1 or 2 based on load and availability. However, I'm being told that the 3750e can not have a virtual IP.

Instead, DNS returns two IPs when I connect to erp.company.com. The client then picks once of these IPs and sends the request. The switch then supposedly routes this physical IP to one of the servers as needed. In other words, if server 1 has IP 1.0.0.1 and server 2 is 1.0.0.2, the switch may route traffic to 1.0.0.2, even if the client request 1.0.0.1.

This just doesn't sound right to me.

Any suggestions on how to properly configure a load balancing/failover configuration with one 3750e switch and two web servers?

I have this problem too.
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Jon Marshall Fri, 06/06/2008 - 08:43

Jens

A number of things don't sound right. The 3750 is not capable of load-balancing between different servers. If you want to load balance you either need

1) A standalone load balancer - Cisco or otherwise.

2) A load balancer that comes on a 6500 module such as the ACE module

3) A switch that is capable of running IOS SLB (Server Load Balancing). The 6500 can do this and from memory the 4948 but please check that.

The 3750 switch will route the packet to IP address that is the destination IP address in the packet. There could be some NAT going on that confuses the issue but generally speaking if you send a packet to 1.0.0.1 and it gets routed by a L3 switch it gets sent to 1.0.0.1.

The only other thing i can think of is HSRP/GLB where there is a virtual address which is tied to a physical address. So you could send a packet to 1.0.0.1 if that was the virtual address on a 3750 and it might actually go to 1.0.0.2. But you are talking about server IP addresses not L3 interface addresses.

Jon

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