ISA Firewalls, NLB and Virtualization

I see a fair number of questions on whether or not NLB works in a virtualized environment. This is an especially important question for ISA Firewall administrators, since NLB is integrated into the Enterprise Edition of the ISA Firewall.

Does NLB work in a VM environment? Well, it depends who you ask. If you check out this blog post at it seems to indicate that NLB will work if all the ISA EE Firewalls are VMs. However, the blog post doesn’t say both multicast and unicast mode will work. However, since he did make a point of saying which method works, I suppose you could assume that both NLB mode will work.

If you’re using VMware, you can’t make that assumption. If you use VMware, only multicast mode NLB will work. Unicast NLB does not work in VMware. This explains why you don’t see me do many articles on NLB, since my VM platform is VMware because of its superior multinetworking features and the ability to save an unlimited number of scenarios and configuration states — something which you can’t do with Virtual PC or Server without a ton of overhead.



Thomas W Shinder, M.D.


Email: [email protected]

MVP — Microsoft Firewalls (ISA)

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