Monday, 15 October 2012

NLB Multicast over routed Subnet -Cisco

Sample Configuration - Network Load Balancing (NLB) Multicast mode over routed subnet - Cisco Switch Static ARP Configuration


NLB Multicast Mode – Static ARP Resolution

  • Since NLB packets are unconventional, meaning the IP address is Unicast while the MAC address of it is Multicast, switches and routers drop NLB packets.
  • NLB Multicast Packets get dropped by routers and switches, causing the ARP tables of switches to not get populated with cluster IP and MAC address.
  • Manual ARP Resolution of NLB cluster address is required on physical switch and router interfaces
  • Cluster IP and MAC static resolution is set on each switch port that connects to ESX/ESXi host
  • Virtual Switch NIC Team Policy > Notify Switches is set to Yes.
  • If CDP (Cisco Discovery Protocol) is Enabled on ESX/ESXi and the Cisco Switch - you can determine proper switch ports connecting to ESX/ESXi via the vSphere/Virtual Infrastructure Client.


To configure the switch:
  1. Telnet in to Cisco Switch Console and log in.
  2. Run this command to enter Configuration mode:

    config t
  3. STATIC ARP RESOLUTION Cisco Global command mode
    For example:

    arp [ip] [cluster multicast mac] ARPA
    arp 03bf.c0a8.0164 ARPA
  4. STATIC MAC RESOLUTION Cisco Global command mode

    For example:

    mac-address-table static [cluster multicast mac] [vlan id] [interface]
    mac-address-table static 03bf.c0a8.0164 vlan 1 interface GigabitEthernet1/1 GigabitEthernet1/2
    GigabitEthernet1/15 GigabitEthernet1/16