Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 
Community Member

Smart solution for Microsoft's Windows NT Load Balancing Service


It possible to configure static MAC entry for multiple ports on Catalyst 3750 platform via "mac-address-table static" command.

So you can run NLB (WLBS) in unicast mode on the same subnet/vlan without extensive unicast flooding.

Relevant IOS configuration entries (NLB server's virtual interfaces are connected to ports 1/0/11 and 1/0/9):

mac-address-table static 00bf.0af0.1453 vlan 1 interface GigabitEthernet1/0/11 GigabitEthernet1/0/9

mac-address-table static 02bf.0af0.1453 vlan 1 interface GigabitEthernet1/0/11 GigabitEthernet1/0/9

This is just an example (VLAN and MAC address).

The first entry is needed for the NLB heartbeat. The second is for virtual cluster MAC address.

On NLB servers You have to disable MAC masking: "MAC address masking is

possible only when the MaskSourceMAC registry key is set to its default

value of one. When it is set to 0, NLB does not perform automatic MAC

address masking". Refer to MS guides on this topic and reboot NLB servers after this reconfiguration.

In this configuration we have only some broadcast traffic caused by NLB heartbeat (1.5Kbps per NLB server).

Multiple MAC static entries seems to be not supported on 2950,4500.




Re: Smart solution for Microsoft's Windows NT Load Balancing Ser

AFAIK, you can't send a unicast MAC to several ports with static entries like you are describing.. this goes against the very concept of switching.

Your best option would be to use multicast NLB and IGMP snooping on the switch instead of unicast NLB if port flooding is your concern.

Alternatively put your NLB servers on a hub and connect it to the switch...

Did it help?

CreatePlease to create content