3Com Knowledgebase Article

Microsoft Network Load Balancing multicast option

3CR17161-91 - 3Com Switch 5500-EI 28-Port

3CR17162-91 - 3Com Switch 5500-EI 52-Port

3CR17171-91 - 3Com Switch 5500-EI PWR 28-Port

3CR17172-91 - 3Com Switch 5500-EI PWR 52-Port

3CR17181-91 - 3Com Switch 5500-EI 28-Port FX

3CR17250-91 - 3Com Switch 5500G-EI 24-port

3CR17251-91 - 3Com Switch 5500G-EI 48-port

3CR17252-91 - 3Com Switch 5500G-EI PWR 24-port

3CR17253-91 - 3Com Switch 5500G-EI PWR 48-port

3CR17254-91 - 3Com Switch 5500G-EI 24-port Chassis

3CR17258-91 - 3Com Switch 5500G-EI 24-port SFP

Com Knowledgebase Article

HP Switch 5500/5500G - NLB Servers cause unicast packet flooding

3CR17161-91 - 3Com Switch 5500-EI 28-Port

3CR17162-91 - 3Com Switch 5500-EI 52-Port

3CR17171-91 - 3Com Switch 5500-EI PWR 28-Port

3CR17172-91 - 3Com Switch 5500-EI PWR 52-Port

3CR17181-91 - 3Com Switch 5500-EI 28-Port FX

3CR17250-91 - 3Com Switch 5500G-EI 24-port

3CR17251-91 - 3Com Switch 5500G-EI 48-port

3CR17252-91 - 3Com Switch 5500G-EI PWR 24-port

3CR17253-91 - 3Com Switch 5500G-EI PWR 48-port

3CR17254-91 - 3Com Switch 5500G-EI 24-port Chassis

3CR17258-91 - 3Com Switch 5500G-EI 24-port SFP

Fix:

1) If the NLB cluster is configured for unicast the only way to reduce the unicast flooding on each switch is to put a static mac address (the Cluster's virtual mac address - 02-bf-xx-xx-xx-xx) in the switches bridge table for the port that points to where the NLB cluster is located. This means that the switch that has the servers that comprise the NLB cluster directly connected to it will still flood that unicast traffic on that switch but the switches in the rest of the network will not - i.e. the NLB cluster is connected to switch 3 - Switch 1 and switch 2 have that virtual mac address assigned as a static address in their bridge table for the uplink port that connects to Switch 3.

2) Try changing the NLB cluster configuration to use multicast instead of unicast. The 5500 allows you to add the sam static multicast mac address to more than 1 port which you can not do if it is a unicast mac address - Assign the multicast virtual mac address used by the NLB Cluster as a static address to the ports connected to the NLB Cluster and any switches in the path to the NLB cluster.

Symptom:

Switch 5500/5500G - NLB Servers cause unicast packet flooding

NLB cluster

Unicast packet flooding

Windows 2003 servers

NLB Virtual mac address

Starting with 02-bf-xx-xx-xx-xx flooded

Cause:

The reason the switch floods this traffic is because you have multiple IP addresses using the same virtual mac address of the cluster. If you have two hosts that are in the cluster you will have 3 different IP's that use the same virtual mac address starting with 02-bf-xx-xx-xx-xx. When a client sends a request to the NLB cluster it uses the virtual mac address. When a host in the cluster responds to the request it spoofs the virtual mac address and changes the “bf” to what it's cluster priority is configured for - i.e 02-01 if its cluster priority is set to 1 - therefore none of the switches will ever learn where that virtual mac address is located and floods all the unicast traffic sent to that NLB clusters virtual mac address.

Fact:

Virtual mac address

Unicast flooding

NLB Cluster configured for unicast