I'm not familiar with Windows servers (I'm some kind of networking guy) but have to setup an ISA server from the networking point of view. It will connect an internal LAN to a DMZ.

There will be a cluster of two ISA servers using NLB. Obviously, the cluster will have 2 NLB "sessions", one for internal and one for DMZ zone. My question is concerning the heartbeat:

What (and why) would be the best way to go out of the following possibilities:

  • 4 NICs per server: dedicated heartbeat segments for both zones (unicast)
  • 3 NICs per server: shared/multinetted heartbeat segment (multicast or unicast?)
  • 3 NICs per server: dedicated heartbeat segments using VLANs on heartbeat NIC (unicast)
  • 2 NICs per server: mixed heartbeat and production traffic on the same NIC (multicast)
  • anything else?

Any pointers are greatly appreciated.


Talking to a number of windows guys the 3 NIC solution with a shared multicast segment for the heartbeat has been chosen. There is no advantage in having two separate hearbeat links, if one side fails, the other one should failover, too. But heaving heartbeat traffic on the production networks is generally a bad idea.

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