Cluster operation mode is very important.
Unicast mode means that NLB takes over the network card it is bound to and doesn’t allow any additional network traffic through it. This is the reason why two adapters are a good idea – one that NLB can take over and one that can still handle all other network traffic directed at the dedicated IP address of the server.
If you’re using a single adapter you should probably select Multicast which allows both the NLB traffic and the native IP traffic to move through the same network adapter. Multicast is slower than Unicast as both kinds of traffic need to be handled by the network adapter but it’s the only way to remotely configure all machines centrally.
You can run a single adapter in Unicast mode, but the cluster manager will not be able to communicate with the server after it’s configured.
As a general rule use Unicast for two adapters, Multicast for a single adapter. With my network cards I had to use IGMP mode in order to get the cards to converge properly – you may have to experiment with both modes to see what works best for you.
资料来源
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Setting up NLB for your WFE’s in SharePoint
http://fabiangwilliams.wordpress.com/2009/04/28/setting-up-nlb-for-your-wfes-in-sharepoint/