# ICMP Router Discovery Configuration

ICMP Router Discovery Protocol (IRDP) is an ICMP message exchange between a host and a router. The security device is the router and advertises the IP address of a specified interface periodically or on-demand. If the host is configured to listen, you can configure the security device to send periodic advertisements. If the host explicitly sends router solicitations, you can configure the security device to respond on demand.

ScreenOS supports IRDP on a per-interface basis. You must assign an IP address before IRDP becomes available on that interface. By default, this feature is disabled. You can configure this feature in a high availability (HA) environment with NetScreen Redundancy Protocol (NSRP).

To enable IRDP on an interface, select the IRDP Enable check box. Enabling IRDP initiates an immediate advertisement to the network.

(Primary IP) is the primary IP address of the security device. Select the Advertise check box and enter a preference status for the security device. The preference status is a number from -1 through 2147483647. Higher numbers have greater preference.

To configure IRDP options, enter the following, then click Apply:

- Broadcast-address: Select this option to broadcast the advertisements. The default address is 224.0.0.1 (all hosts on the network).

- Max Advertise Interval: Maximum number of seconds that pass between ICMP advertisements. The default value is 600 seconds. The valid value range is from 4 through 1800 seconds.

- Lifetime: Number of seconds for the lifetime of the advertisement. By default, the lifetime value is three times Max Advertise Interval. You can also set the lifetime value. The valid value range is the Max Advertise Interval through 9000 seconds.

- Min Advertise Interval: Lower limit (in seconds) of the advertisement period, which is calculated to be 75 percent of the value entered for Max Advertise Interval. You can also specify a number from 3 through the Max Advertise Interval value. When you change the Max Advertise Interval value, the Min Advertise Interval value is automatically calculated.

- Response Delay: Number of seconds to delay response to a client solicitation. By default, the security device waits for 0 to 2 seconds before responding to a client solicitation request. You can change the default setting from no delay (0 seconds) to up to a 4-second response delay.

- Init Advertise Interval: Number of seconds during the IRDP startup period allocated for advertisement. The valid value range is from 1 through 32 seconds. By default, this period is 16 seconds.

- Init Advertise Packet: By default, the security device sends out three advertisements during the specified startup period (Init Advertise Interval). The valid value range for the number of advertisements sent is from 1 through 5.

To disable IRDP, deselect the Enable check box. Disabling this feature causes all IRDP-related memory for this interface to be removed.