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In order to keep the number of servers down in a high availability environment, administrators have been looking at using Network Load Balancing (NLB) for CAS and then co-locating the HT role on each node of the NLB cluster to also provide high availability for the HT role. This configuration can work, and it really is not too difficult to configure. It is extremely important to note that using NLB to load balance the default SMTP receive connectors (using port 25) is not supported and is completely unnecessary since they are load balanced for all intra-Exchange communications like HT to HT … Continue reading Exchange Server 2007 Hub Transport (HT) and Client Access Service (CAS) on the Same NLB Cluster – Updated Jan 9, 2008

I learned something new yesterday. It kind of flipped me out, but now it almost makes sense.   You can try this to confirm. From a client, ping the IP address of your NLB cluster. From the same client, run arp -a fom the command prompt. You should see something like this (I will assume 192.168.2.11 for the NLB cluster IP address):     Internet Address         Physical Address      Type     192.168.2.11            02-bf-c0-a8-02-0b     Dynamic   It will list other addresses and their MACs as well, but we are only interested in the NLB address. 02-bf-c0-a8-02-0b breaks down into nice little components like so: The first … Continue reading Network Load Balancing and MAC Addresses

The quick summary of this post is, “Don’t use NLB on teamed NICs.” Microsoft clearly says that NIC teaming “may” cause problems with NLB in KB 278431. This is where things get confusing, because the issue is just that; it may be a problem. The reasoning is really fairly simple. Teaming software, in many cases, overwrites the MAC address of the individual NICs in the team. Well, NLB, in Unicast, also overwrites the MAC address. So, the problem is: Will the teaming software allow the overwrite behavior of Unicast? Will the teaming software handle the failure of a NIC in the … Continue reading Network Load Balancing (NLB) and Network Interface Card (NIC) Teaming

As usual, confusion motivates me to blog some more. In this case, I have blogged this because I was confused, and I am pretty sure that I have it straight now. Comments may prove me wrong. When designing, planning, testing, and implementing Network Load Balancing (NLB) Clustering, a choice has to be made regarding unicast vs. multicast. There are a few differences, but the main difference is in the way MAC addresses are implemented. Unicast – Each NLB cluster node replaces its real (hard coded) MAC address with a new one (generated by the NLB software) and each node in the … Continue reading Unicast vs. Multicast – Original Posted Feb 21, 2005

As usual, confusion motivates me to blog some more. In this case, I have blogged this because I was confused, and I am pretty sure that I have it straight now. Comments may prove me wrong. When designing, planning, testing, and implementing Network Load Balancing (NLB) Clustering, a choice has to be made regarding unicast vs. multicast. There are a few differences, but the main difference is in the way MAC addresses are implemented. Unicast – Each NLB cluster node replaces its real (hard coded) MAC address with a new one (generated by the NLB software) and each node in the … Continue reading NLB Unicast vs. Multicast – Original Posted Feb 21, 2005