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Network issues caused by Microsoft NLB

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Network issues caused by Microsoft NLB

Postby blin » Thu Jan 12, 2012 11:36 am

We have found some of our clients have these issues that are caused by Microsoft NLB.

Case 1: CAS keeps shutdown by itself. We fix this problem by removing NLB cluster from Exchange CAS servers.

case 2: Some network devices such as wireless AP and time clock keep losing the connection. If we put these devices on different subnet or VLAN they work fine.

Case 3: The client is running web servers on dual node Windows Network Load Balancing (NLB) servers running in IGMP multicast mode. They run it on machines with two network cards. The cluster address is on one NIC and the nodes answer on another. The cluster address answered if you called it from another host on the subnet that the cluster was installed on. However, if you were off subnet it didn't answer. This is suboptimal for a web server
Solution for this problem: by default IP Forwarding is not enable in Windows 2008. This is the feature of Windows networking that, in the context of NLB, allows responses to requests sent to one NIC to be routed out the other. It's fixed by using one specific command line option.
(Make sure you are using a command prompt with administrative privlidges)
netsh interface ipv4 set int "[name of the NIC]" forwarding=enabled
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blin
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Location: Chicago, USA

Re: Network issues caused by Microsoft NLB

Postby blin » Thu Jan 12, 2012 11:45 am

I am also facing a similar issue with Windows 2008 NLB when configured in unicat mode is not accessible from other subnet.

I have two NIC cards.

One nic card of both hosts is connected to nortel switch and assigned IP address 10.X.X.X with NLB enabled (local Area Connection).

Another NIC of both hosts is connected via crossover cable and assigned IP address 192.168.X.X (heartbeat).

It works fine when changed to multicast mode. However, I want itto run in Unicast mode.

I run the command you mentioned that is

--netsh interface ipv4 set int "Local Area Connection" forwarding=enabled

Still, i am not able to acess the cluster across the subnet. Running abve command created some issue with server accessing the DC/DNS servers. So, I had to revert it.
How to Configure and Troubleshoot Cisco
http://www.howtocisco.com

Tablet and Smartphone Setup Guide
http://www.quicksetupguide.com
blin
Site Admin
 
Posts: 2790
Joined: Wed Dec 31, 1969 7:00 pm
Location: Chicago, USA


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