Cisco switch, Microsoft Windows Network Load Balancing.

As part of our new site roll-out we’re using quite a few servers. Some are running in tandem while others are complete backups just in case. Basically, for every function we’re running at least 4 servers (2 load balanced front-facing, 1 backup, and 1 dev/testing).

Using load balancing is a little more tricky on our environment.

On the test environment, which is strictly a vmware server with a crap-load (technical term) of virtual machines, the Microsoft Load Balancing works without any problems. Create a virtual IP, point both servers to it, and away you go.

Unfortunately for us this didn’t work so well on the live production servers. Why? The servers required multicast load balancing. Cisco switches don’t work well with multicast load balancing. The router refuses to learn the ARP for the IP address if it’s coming from a multicast MAC. I had previously switched the servers to unicast, which solved the problem within the Cisco switches, but then the applications would not function on the servers.

One must create a Static ARP Entry on the gateway switch.

For this exercise I have a switch (192.168.1.245) and a server (192.168.1.173) and a client (192.168.2.202) all of which are Class C /24 255.255.255.0 addresses. You will need to know the IP of your server’s Virtual IP (the one for load balancing) and the MAC address of the virtual IP. Easy way to find this is to open a cmd window and type the following:
arp -a 192.168.1.173
OR you can open the network load balance manager and find it listed on the first screen under MAC/physical address.

Now we need to configure your switch

Telnet to your device
Type in your password
Go to enable mode
en
Configuration terminal
config t
arp 192.168.1.173 0100.7f5e.ad01
end
wr mem

Now your pings should work.