Continue Reading This Article. The way Microsoft's NLB operates (always for Windows 2000, and by default for Windows 2003) is to send outbound traffic using a MAC address that is not the same as the MAC address it sends in its ARP Response. The result is, that the inbound traffic is coming to a MAC address that does not exist in the switch's FDB. NLB is not supported in max-host system routing mode. NLB multicast mode is not supported on Cisco Nexus 9500 or 9300 Series switches. Note: To work around the situation of Unicast NLB limitation, we can statically hard code the ARP and MAC address pointing to the correct interface. Re: Microsoft NLB Support. If the NLB is working in multicast mode, so the only thing you have to do is to configure a static multicast mac-address entry in each port that the server is connected to, as a static ARP resolution to the virtual IP and MAC address of the NLB. At the other hand, there was a limitation - in most of players.
We currently leverage Windows NLB (unfortunately) to 'load balance' our ADFS and Direct Access servers.
These servers are set up with IGMP Multicast. Our router is set up as an IGMP Querier. This has all worked for months and months.
When an IGMP Querier isn't set up of course, you can't ping the virtual IP outside the local subnet because you are dealing with a a unicast IP and a multicast MAC Address. I'm experiencing this issue on some of our switch stacks all the sudden. No changes were made.
We have 2 4500X that act as our core, and then various 2960X switch stacks.
I'd be glad to provide any information in detail that is needed but figured I'd just toss out some basic information to start with.
