Windows Load Balancing over many subnets; how many IP addresses are required

load balancingnetworkingnlbwindows-server-2008windows-server-2008-r2

I have two hosts that have an interface in 4 different LAN subnets (no WANs apply here). 

10.1.1.x
10.1.2.x
10.1.3.x
10.1.4.x

Assume that each subnet will need a local service of x.x.x.9 as the desired service to be load balanced. Also assume the two hosts already have the following non load balanced IPs:

10.1.1.11
10.1.1.12

Question

When I set up NLB on the other subnets, am I required to also have a non clustered IP for that host?

Example:

Load Balanced
10.1.1.9
10.1.2.9
10.1.3.9
10.1.4.9


Host1
10.1.1.11  <-- Already Exists
10.1.2.11  <-- Is this needed in addition to 10.1.x.9??
10.1.3.11  <-- Is this needed in addition to 10.1.x.9??
10.1.4.11  <-- Is this needed in addition to 10.1.x.9??


Host2
10.1.1.12  <-- Already Exists
10.1.2.12 <-- Is this needed in addition to 10.1.x.9??
10.1.3.12 <-- Is this needed in addition to 10.1.x.9??
10.1.4.12 <-- Is this needed in addition to 10.1.x.9??

In other words, must all the IPs on this page be on the same subnet?

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Best Answer

On each subnet, each server part of the nlb cluster need one ip (it's own) and then one or more virtual ip addresses.

What affect the behaving of NLB is the choice between unicast and multicast: http://technet.microsoft.com/en-us/library/cc782694(v=ws.10).aspx

servers needs one dedicated ip per subnet because you don't manually map the cluster ip to network interface. NLB uses ip interfaces to detect on which network card to publish clusters IP.

Unicast change mac address but need generally to configure switch (which by default don't accept same mac address on more than one port)

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