Network Load Balancing

NLB Considerations and Restrictions

Although the switch interoperates with NLB clusters that operate in Unicast mode and Multicast mode, the following restrictions apply:

• True egress mirroring is not supported on all VOSS hardware platforms. Because packets are mirrored prior to the completion of packet processing, egress mirrored packets can differ from the packets egressing the port. Therefore, NLB Unicast traffic and NLB Multicast traffic destined to the NLB Virtual Mac Address are not mirrored correctly.

  

  Note

  To mirror the egress traffic of VOSS hardware platforms, you can use the NEXT-hop device ingress mirroring to capture the egress packets of the switch.

  Of the VOSS hardware platforms, only VSP 4450 Series supports true egress mirroring.

• Inter-VRF routing is not supported between an NLB client and an NLB cluster VLAN in Unicast mode or Multicast mode.

• You must configure NLB to use the same mode as the NLB Server.

• Static ARP entries are not supported for NLB Unicast or NLB Multicast.

• For interoperability with NLB, the switch provides configuration options at the VLAN level.

• ARP entries for NLB server IP addresses do not age out when there is still client traffic coming to the NLB servers, even after the NLB servers are no longer reachable.

NLB Clustering in Unicast Mode

When the cluster is running in NLB unicast mode, all servers in the cluster share a common virtual MAC address, which is 02-bf-x-x-x-x (where x-x-x-x is the cluster IP address in hexadecimal form). All traffic destined to this MAC address is sent to all the servers in the cluster. The virtual MAC address is specified in the Sender MAC Address field of the Address Resolution Protocol (ARP) reply from the cluster to the switch. ARP responses from the switch are sent to the virtual MAC address (rather than to the hardware MAC address).

You can configure the switch for NLB unicast mode support. After you enable the NLB unicast option, the switch floods traffic destined to the cluster IP address to all ports on the VLAN. Unicast mode supports connectivity to a secondary virtual IP address. For information about software scaling capabilities in unicast mode, see VOSS Release Notes.

NLB Clustering in Multicast Mode

When the cluster is running in NLB multicast mode, a multicast virtual MAC address with the format 03-bf-x-x-x-x (where x-x-x-x is the cluster IP address in hexadecimal form) is bound to all cluster hosts but the real MAC address of the network adapter is retained. The multicast MAC address is used for client-to-cluster traffic, and the real MAC address of the adapter is used for network traffic specific to the host server.

You can configure the switch for NLB multicast mode support. When you enable NLB multicast mode on a VLAN, the routed traffic destined to the NLB cluster is flooded by default on all ports of the VLAN. All VLANs support multiple cluster IPs by default. You can connect up to 200 NLB clusters to a single VLAN. For information about software scaling capabilities, see VOSS Release Notes.

Note

Shortest Path Bridging MAC (SPBM) supports NLB Unicast and Multicast modes. For more information on SPBM, see Fabric Basics and Layer 2 Services.