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Using Network Load Balancing in unicast mode and allowing the servers to communicate

Posted on 2009-02-19
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Hello,

Taking this question a step further,
http://www.experts-exchange.com/OS/Microsoft_Operating_Systems/Server/2003_Server/Q_22784244.html?sfQueryTermInfo=1+balanc+load+network

IS there a way to make two servers in a cluster communicate with each other while using Unicast with one NIC?  Two NICS?

We have two front end Windows 2003 Exchange 2003 servers in an NLB using unicast.  There are two NICS present. NLB is bound to 1 nic on each.

Our problem is that since these are both front ends, i would think Exchange would like to pass information between these two from time to time, but instead has to route a different way.  This is noticable if you make one server a bridgehead for a connector, but not the other.  A delay will occur (knowing full well that these servers need to be configured the same since they are in an NLB cluster but that is just an example).

Do I need to change to multicast after confirming my switch will allow that?

Thanks,
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Question by:Rachel Flewelling
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Expert Comment

by:oBdA
ID: 23690296
In Unicast mode, these servers won't be able to communicate with each other, because they're sharing the same MAC address on the NLB NIC.
You'll either need to add a second NIC (which can cause other problems related to DNS registrations and multihoming; these aren't DCS?), or change to Multicast (which, on the other hand, may cause problems accessing the NLB address from outside the servers' subnet, because most routers don't publish Multicast addresses).
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by:Rachel Flewelling
ID: 23693226
oBdA (great name by the way),

Not DCs. They do already have 2 active NICs each (NLB cluster only on one NIC each).

As a test, I quickly switched the NLB cluster to multicast and after the cluster settled, it went totally offline. Was unable to ping any host or the cluster IP.

Talking to my Networking co-worker, he stated that the ARP table on the switches problaby had the old entries and wouldn't refresh for maybe 4 hours.  We have a complete power down coming tomorrow which will take all systems down.  I'm thinking I can switch to multicast before shutdown, and when everything comes up give it a try and if all fails, go back to unicast for now.

Regarding accessing the NLB address from outside the servers' subnet, that may be a problem.  We use Vlans to segment traffic so our subnets are few but large... however some remote sites have different subnets.  We will have to test this...

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Expert Comment

by:oBdA
ID: 23694203
If there are two NICs in there, and the non-NLB NIC is active, then the servers should be able to communicate over this one (if they can reach each other through this connection). If you haven't done so already, you should unbind NetBIOS over TCP/IP from one of the NICs (ideally on the NLB NIC).
Here is some further

Network Load Balancing: Configuration Best Practices for Windows 2000 and Windows Server 2003
http://www.microsoft.com/technet/prodtechnol/windowsserver2003/technologies/clustering/nlbbp.mspx

Network Load Balancing Frequently Asked Questions
http://www.microsoft.com/technet/prodtechnol/windowsserver2003/technologies/clustering/nlbfaq.mspx

How Network Load Balancing works
http://technet2.microsoft.com/windowsserver/en/library/3b98db33-e748-4a75-a0af-e445569655be1033.mspx?mfr=true

Using Clustering for a Highly Available Web Site: An Example
http://technet2.microsoft.com/windowsserver/en/library/1d737be7-7f83-471f-8601-e756195864ec1033.mspx

Network Load Balancing clusters
http://technet2.microsoft.com/windowsserver/en/library/98d46a24-96d8-412c-87d8-28ace62323d21033.mspx?mfr=true

Network Load Balancing Best practices
http://technet2.microsoft.com/windowsserver/en/library/fa6ef832-1aa7-472f-b492-0dd3c60bd46d1033.mspx?mfr=true
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Author Comment

by:Rachel Flewelling
ID: 23694500
Currently,
NIC1 public subnet has Netbios over TCP off
NIC2 private subnet has Netbios over TCP on

I should explain the 2 NIC setup because that may cause your Netbios suggestion to not work.

Server1.domain.com
Cluster bound NIC1 IP address 10.100.226.135 , 255.255.255.0
NIC2 IP address  172.1.226.135 , 255.255.255.0 - TSM backup system uses this NIC. This subnet cannot communicate with the NIC1 subnet. However, can ping the 172 IP address of Server2.

Server2.domain.com
Cluster bound NIC1 IP address 10.100.226.136, 255.255.255.0
NIC2 IP address 172.1.226.136, 255.255.255.0 - TSM backup system uses this NIC.  This subnet cannot communicate with the NIC2 subnet however can ping the 172 IP address of Server1.

Cluster IP
10.100.226.137, 255.255.255.0

The NIC2 subnet is only used locally, the TSM server is on the same range, no gateway or routing needed.

I have reviewed those links above and I understand what I'm doing and why they cannot communicate with each other. However, my management would like to see these two servers be able to read each others mail queue information in ESM for example.  
They understand why this happens (I showed them the assigned MAC address to all the cluster IPs) but if there is a way to let them operate as normal AND have them in a NLB cluster I need to find out.

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Author Comment

by:Rachel Flewelling
ID: 23694663
I should add, that I have the ability to activate another NIC on each machine and put that on the same subnet as NIC1. They exist but are disabled with no cable.  (each server has 4 nics). Solution?

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Accepted Solution

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oBdA earned 2000 total points
ID: 23704937
Adding another NIC in the 10 subnet would enable the inter-host communication, yes. In this case, disable DNS registration for all NICs.
Instead, manually create DNS entries with the host names of the servers pointing to the "new" IP addresses, and (if required) dedicated names for the NLB NICs (and the clustered IP).
Example:
172.1.226.135        DNS: exch1-tsm   \
10.100.226.145       DNS: exch1       | Exchange host 1
10.100.226.135       DNS: exch1-nlb   /
  |
  +--10.100.226.137  DNS: exch
  |
10.100.226.136       DNS: exch2-nlb   \
10.100.226.146       DNS: exch2       | Echange host 2
172.1.226.136        DNS: exch2-tsm   /

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Author Closing Comment

by:Rachel Flewelling
ID: 31548986
Information is clear and understandable.  Thank you.
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