Disabling GARP and ND for out-of-subnet Addresses

You can configure the SBC to limit its use of Gratuitous Address Resolution Protocol (GARP) or Network Discovery (ND). Specifically, you can prevent the system from performing this function for each sip-interface that is not in the same subnet as the network-interface on which they operate. External systems typically reach these addresses through static routes or other routing configurations, making the use of GARP and ND unnecessary for them.

The SBC sends out a GARP or ND message, for IPv4 or IPv6 respectively, for every configured interface and VLAN during every interface initialization, HA switch over, and media link up event. When the number of configured interfaces and VLANs are large, the SBC may send thousands of these GARP or ND in a very short amount of time. Such GARP avalanches can overload the routers and switches connected to the SBC.

The SBC's GARP rate limiting feature helps to avoid overload to some extent. You can further limit the amount of GARP and ND traffic issued by the SBC when you enable the disable-garp-out-of-subnet parameter within the system-config. When enabled, this feature prevents the system from issuing GARP or ND messages for every sip-interface that is not in the same subnet as the network-interface over which they operate. Enabling this parameter also prevents the system from issuing GARP or ND messages to loopback interfaces.

Use the syntax below to enable this parameter.

ORACLE(system-config)#disable-garp-out-of-subnet enabled

This parameter is Real Time Configurable.

Note:

Although the disable-garp-out-of-subnet parameter is visible on the Subscriber Aware Load Balancer (SLB), it does not apply and has no effect on that product.

Reporting

You can refer to the log.l2resolver log for information about this feature. This log presents the total number of entries in the NDP table, the number of NDP entries chosen for GARP processing and the number of out-of-subnet interface IPs that the feature has filtered out.