Enable and Disable VLAN Flooding
• The older ARP entries are overwritten whenever newer NLB entries are learned.
• All ARP entries, learned after the feature is enabled, are deleted when the feature is disabled, and RP2
triggers an ARP resolution. The feature is disabled with the no ip vlan-flooding command.
• When a port is added to the VLAN, the port automatically receives traffic if the feature is enabled. Old
ARP entries are not deleted or updated.
• When a member port is deleted, its ARP entries are also deleted from the CAM.
• Port channels in the VLAN also receive traffic.
• There is no impact on the configuration from saving the configuration.
• The feature, if enabled, is displayed in the show running-config command output that displays the
ip vlan-flooding CLI configuration. Apart from it, there is no indication of the enabling of this
capability.
Configuring a Switch for NLB
To enable a switch for unicast NLB mode of functioning, perform the following steps:
Enter the ip vlan-flooding command to specify that all Layer 3 unicast routed data traffic, going
through a VLAN member port, needs to be flooded across all the member ports of that VLAN. There
might be some ARP table entries that are resolved through ARP packets, which had the Ethernet MAC
SA different from the MAC information inside the ARP packet. This unicast data traffic flooding
occurs only for those packets that use these ARP entries.
CONFIGURATION mode
ip vlan-flooding
To enable a switch for multicast NLB mode of functioning, perform the following steps:
1. In the multicast mode of NLB, add a static ARP entry by entering the arp ip-address
multicast-mac-address command in Global configuration mode to associate an IP address with
a multicast MAC address in the switch. This setting causes the multicast MAC address to be mapped
to the cluster IP address for the NLB mode of operation of the switch.
INTERFACE mode
arp ip-address multicast-mac-address interface
2. Associate specific MAC or hardware addresses to VLANs.
CONFIGURATION mode
mac-address-table static multicast-mac-address vlan vlan-id output-range
interface
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