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Nexus 9372PX and Microsoft NLB


Hi all,

I have the following setup:

2 Nexus 9372PX (NX-OS Release 7.0(3)I1(1a) ) in a VPC-Configuration

4 Nexus 2248TP-E, 2 are attached to Nexus_1, 2 are attached to Nexus_2

Attached to one of the FEXs is a Microsoft NLB (mac_addr 03bf.0a04.023c, ip_addr, which is configured for Multicast-Support.

Customer is using Microsoft NLB for MS Exchange.

I've added a static ARP-entry on both 9372PX (see below)

interface Vlan42
  ip address
  no ipv6 redirects
  ip arp 03BF.0A04.023C
  hsrp version 2
  hsrp 42
  ip dhcp relay address
  ip dhcp relay address


Clients are connected to several VLANs, eg. VLAN 8 (; SVIs are configured on the Nexus 9372PX.

I tried to add the following command which gave me the error-msg since this is obviously not supported on Nexus 9372PX.

mac address-table static 03BF.0A04.023C vlan 42 interface po 41
ERROR: Multicast/Broadcast MACs are not supported!

Since we migrated from an old Catalyst 4510R, we are facing extremely slow response-times or even time-outs in MS Outlook.

We are looking for a good workaround.

Any hint or tipps are very much appreciated.

Best regards





4 Replies 4


Hi Roman,


Unfortunately, as far as I am aware there is no workaround at this point in time. This deployment method of NLB is not supported on the Nexus 9000 platform as documented in the NX-OS release notes.


You could reconfigure the NLB cluster to unicast mode and follow the advice in for a better outcome.

Alternatively you could migrate from NLB to a hardware load balancer solution. The Nexus 9000 platform has built in load balancing capabilities with the Intelligent Traffic Director (ITD) function.

Hi Nicolas,

thank you very much for your reply.I've already checked CSCuq03168. Do you eventually have any infos about the timeframe Nexus 9300 will support this deployment ?

In the meantime we configured the MS-NLB to unicast without following TAC doc 118951. Unfortunately we were not very successful - we were even not able to access the VIP anymore.

So my next thought is to try IGMP, which is supported on MS NLB running under Windows Server 2008 R2.

Do you have any experience with this ?

I really appreciate again your reply


Did you happen to get this working? Running into your same situation on a 9300

No, we did not. I recommended the customer to use ITD as loadbalancing mechanism instead of MS NLB. This means that we had to buy the network services license for the 2 Nexus. 

Until now we don't have new feature in place due to some time constraints @the customer.

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