Microsoft NLB on Nexus 5596T

rramlal · ‎07-22-2013

Hi guys,

We recently installed two 5596T in a cluster at a customer. They are currently migrating their servers to a VMWARE solution and have asked if the nexus supports microsoft NLB on multicast mode.

I reached to Cisco TAC on this however I havent gotten any confirmation on the commands that are required. Can you advise what commands are required for this to allow servers to see the NLB server. So far the customer are able to migrate and the solution is working however is it recommended to set static maps on the nexus for the nlb server?

Thanks much.

richbarb · ‎07-22-2013

Hi,

Look this document, I applied this configuration once and worked fine.

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There are 3 modes to Microsoft Network Load Balancing (NLB)

1. 1.Unicast

2. 2.Multicast

3. 3.IGMP multicast (check the IGMP checkbox in the GUI while in multicast mode)

In general,every mode uses a different sending and receiving mac address while keeping the unicast virtual IP address (VIP) constantacross all 3 modes. This concept makes switches flood traffic at layer 2 since the switch either never sees the destination mac address come in on any of its ports(and hence can’t learn it) or the multicast mac address floods. Either multicast mode, IGMP or normal multicast, also requires static ARP entries on the gateway router since Cisco routers will not learn an ARP reply with a multicast mac address tied to a unicast ip address.

Mac addresses in the 3 modes breakdown into the following components:

The first number in the mac address is the type of NLB configuration: 01=IGMP, 02=Unicast, 03=Multicast (Note: bit 2 is the administered locally multicast space)
The second number, (bf) is the same for unicast and multicast mode (not IGMP multicast mode which uses the standard 01-00-5e mac address)
The last two (IGMP multicast mode) or four (unicast or multicast mode) numbers are the virtual IP address, i.e. c0=192, a8=168, 04=4, 0a=10 and thus the IP of 192.168.4.10 has a multicast mac address 03-BF-C0-a8-04-0a while an IGMP multicast mac address would be 01-00-5e-7f-04-0a

Summary of configuration

NLB mode	Switch configuration	Router configuration
Unicast	Mac address-table static 02bf.xxxx.xxxx vlan y interface	Not required – unicast mac address with unicast ip address
Multicast	Mac-address-table static 03bf.xxxx.xxxx vlan y interface n7k[5.2(1)]: mac address-table multicast 03bf.xxxx.xxxx vlan y interface	Arp 03-bh-xx-xx-xx-xx arpa
IGMP multicast	Mac address-table static 01005exx.xxxx vlan y interface	Arp 01-00-5e-7f-xx-xx arpa

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Basicly you have to add the mac address static to all ports that you learned the mac address of your cluster microsoft (including the vpc peer-link if exist).

In the router (could be the N5K, if it doing the L3 boundary) you have to add the arp entry in the vlan sub-interface configuraton mode.

The cluster comes up instantly.

Richard

rramlal · ‎07-22-2013

Thanks for the response. The server is actually virtualised and it is working now since they are directly connected to a 3com switch that uplinks to the nexus 5k.

This is temporary as they would be moving to the 10gb links that are directly connected to the 5k. The server network is flat and the L3 interface is the firewall not the n5k. So with this in mind should i statically add the mac address static to the 10GB interfaces alone since the microsoft server traffic will be coming from that link. Since that link will be a trunk uplink for the vmware cluster, how will this be affected. Please advise?

richbarb · ‎07-24-2013

No problem at all, in the N5K you have to add all interfaces possible may to learn the mac address virtual from the cluster, even it is a trunk or share another traffic.

As your firewall is doing the routing to your networking, the step to add arp entry in the router isn't necessary.

The microsoft cluster that i tested worked in the "multicast" mode. I haven't tested the other options available.

Richard

Devavrat Oka · ‎08-30-2013

Second that. mac addresses have to be statically added on NX5K switches when using MS-NLB. If the SVI for the VLAN is on the 5K, the 5K will complete arp for the servers.

Adam Bragg · ‎06-26-2014

When we added the static MAC to the vpc peer-link on one of the switches, the NLB would work. If we added the static MAC to both sides of the vpc peer-link, the traffic would fail.

Has anyone else seen this behavior? Can anyone explain this behavior?

Thanks.