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Microsoft NLB with UCS & Upstream Nexus 7000



I know lot of users is using NLB & My concern is if everybody can chip in with their idea we can make this question & convert to the document .

We are trying to setup the Microsoft NLB with UCS  Enviornment. I have 3 Chassis connected to 6120 which in turn connected to vPC to pair of nexus 7k.

I have configured NLB with multicast option with Sinlge NIC. Multicast Mac address is 03-BF-XX-XX-XX-XX ( where xx is mapped digit of Ipv4 of cluster Ip)

I have configured static arp  on the Nexus 7k with VIP :

LB1 IP/MAC                   VIP ( Virtual IP or Cluster IP)       

0050.5697.0001           03-BF-0A-0A-0A-0A



I have static arp on  nexus 7k with map to 03-bf-0a-0a0a-0a

Before static arp I could not ping cluster ip from outside this subnet ( well known issue with NLB )

After creating static arp I could ping cluster ip & nlb seems to work but when I do the Etheral capture on Lb1 & lb2 ,it shows me destination mac as 0050.5697.0001 on lb1 & lb2 0050.5697.0002 . on 6120 , I do not see any mac address reference to 03-bf-... , I am puzzled how this thing working.



5 Replies 5

Mathew Lewit
Cisco Employee
Cisco Employee

I am not sure if you are aware of this issue on UCS.

But in order for multicast to work you will have to enable the querier upstream (not sure if you have done this or not).

Hi Mathew,

thank you for the reference bug id . I have set NLB cluster mode with multicast ( there are 3 option , unicast,multicast & igmp multicast ). Igmp multicast option use standard 01:00:5e: format while multicast option use that 03-bf-xx- mac address.

As far as I know igmp snooping will control how multicast traffic forward at layer 2 ( it will snoop the conversation & flood to only port that are interested). Regardless of it, I am not using igmp multicast mode .

Weird part is I have arp set for virtual ip to 03-bf- & UCS does not know about this mac address , it knows individual lb1 & lb2 mac address. According to

unknown mac Fabric Interconnect will drop the packet. In my case it's forwarding the traffic & when I do Ethereal Capture at the lb1 & lb2 I am seeing the mac address of lb1 & lb2 ..




Have you configed the "peer-gateway" option at the vPC ? I have the experience about that when used vPC in front of the F5 NLB device.

Sent from Cisco Technical Support iPad App

Hi Gary,

I have peer-gateway enabled for my NAS Storage & this is not a issue at all here, I have NLB working in this instance.

I could not figure out how when I have static arp sate on Nexus 7k for to

03-bf-0a-0a-0a-0a & ping works fine but when I do ethereal Capture on LB1 or LB2 it shows LB1 & LB2 mac address .\

Thank you


As the LB1 and LB2 never use the cluster MAC to send any traffic out, all layer 2 devices wont see the cluster MAC as source MAC of ethernet frame. So you wont see cluster MAC in their MAC address table.


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