NLB Will Actually Converge On A Crossover Cable

...It's just that it's of no use to anyone outside the cluster - and I can't think of a way of making anything useful happen using a crossover cable within an NLB cluster, so if anyone's got a good usage scenario for Wibbles with a crossover cable, please leave a comment!


In the course of a support issue I was working on, the possibility of testing NLB (aka WLBS ="Wibbles") convergence with a crossover cable came up. I couldn't think of a good reason that it wouldn't work, but the title of the following article made me look at it again:


242248 Using crossover cable causes load balancing not to work


The title seems pretty straightforward, but it seemed to contradict what we know about Wibbles from NLBTech2 - which is that as long as there's a common broadcast plane for the heartbeat traffic to work across, convergence should work.


When you take a closer look at the contents of the article, the actual meaning becomes clearer:


other devices on the same subnet may not be able to ping the cluster IP address, or may not be able to gain access to TCP services configured for load balancing.
This behavior can occur if the cluster nodes are connected by using a crossover cable between the cluster adapters.
Remove the crossover cable and attach the cluster adapters to the same network as the dedicated adapters.


So what the article is actually saying is that if the clients aren't connecting to the NLB adapters directly, they can't connect. Which is cool, it's what we expect!


For those focused on troubleshooting this type of thing, and who like resolutions, in the case I was working on the Gigabit Ethernet adapters weren't converging when in Multicast mode, even with a crossover cable, though Unicast was working fine. A driver upgrade solved the problem.


If you're ever troubleshooting an NLB/WLBS convergence problem, a good "master" article to start with is this one:
812870 Network Load Balancing Cluster Node Does Not Successfully Converge

Comments (4)

  1. Nad J says:

    Two things:

    For me changing from Multicast to Unicast didn’t solve the problem with the cross over cable.

    When all 4 interfaces were plugged to the same switch it worked for about an hour then broke off. Something weird happened though. NIC 1 on Machine A couldn’t see the NLB on NIC 2 on Machine B and vice versa.

    Swapping the cards used for NLB resolved the issue for a while then went kaput again. I am still convinced it’s a lack of compatible drivers that are causing convergence issues.

  2. Nad J says:

    And literally, just now, having updated the NIC driver – hey presto!

  3. TristanK says:

    Glad it worked for you! If you’re able to name your NIC and current (working) driver revision, I’d appreciate it!

  4. Franz says:

    Broadcom NetXtreme gigabit ethernet for me.

    Recent HP link for 4 Mar 04 driver-

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