Router Discovery

The ICMP Router Discovery protocol is an IETF standard protocol that allows hosts running an ICMP router discovery client to learn dynamically about the presence of a viable default router on a LAN. It is intended to be used instead of having hosts wiretap routing protocols such as RIP. It is used in place of, or in addition to, statically configured default routes in hosts.

	Note - Only the server portion of the Router Discovery Protocol is supported.

Gaia implements only the ICMP router discovery server portion, which means that a Check Point router can advertise itself as a candidate default router, but it will not adopt a default router using the router discovery protocol.

The ICMP Router Discovery Service provides a mechanism for hosts attached to a multicast or broadcast network to discover the IP addresses of their neighboring routers. This section describes how you can configure a router to advertise its addresses by using ICMP Router Discovery.

How Router Discovery Works

The router discovery server runs on routers and announces their existence to hosts. It does this by periodically multicasting or broadcasting a router advertisement to each interface on which it is enabled. These advertisements contain a list of all the router addresses on a given interface and their preference for use as a default router.

Initially, these router advertisements occur every few seconds. They then fall back to every few minutes. In addition, a host can send a router solicitation, to which the router responds with a unicast router advertisement. However, if a multicast or broadcast advertisement is due in a moment, the router does not respond with a unicast advertisement.

Each router advertisement contains an advertisement lifetime field indicating the length of time that the advertised addresses are valid. This lifetime is configured such that another router advertisement is sent before the lifetime expires. A lifetime of zero (0) indicates that one or more addresses are no longer valid.

On systems that support IP multicasting, the router advertisements are sent by default to the all-hosts multicast address 224.0.0.1. However, you can specify the use of broadcast. All IP addresses configured on the physical interface are included in the router advertisement when:

Router advertisements are sent to the all-hosts multicast address, or
An interface is configured for the limited-broadcast address 255.255.255.255.

When the router advertisements are sent to a net or subnet broadcast, only the address associated with that net or subnet is included.

Configuring Router Discovery - WebUI

To enable router discovery services:

Open the Advanced Routing > Router Discovery page of the WebUI.
Click Add.
The Add Interface window opens.
Select the Interface on which to enable Router Discovery.
Optional: Enter values for the Router Discover Configuration parameters.
- Enable Router Discovery
- Min. Advertise Interval
- Max. Advertise Interval
- Advertisement Lifetime
Optional: For each IP address on the interface, define the Router Discover Configuration parameters:
- Advertise
- Eligibility
- Preference
Click OK.
Click Save.

To disable router discovery service on an interface:

Open the Advanced Routing > Router Discovery page of the WebUI.
Select an Interface and click Edit.
Clear Enable Router Discovery.
Click Save.

Router Discover Configuration parameters

Parameter	Description
Interface	The interface on which Router Discovery occurs.
Enable Router Discovery	Whether ICMP router discovery is running on the interface. After you enable ICMP router discovery, configuration options for the interface appear. Default: Unselected
Min. Advertise Interval	The minimum time (in seconds) allowed between sending unsolicited broadcast or multicast ICMP Router Advertisements on the interface. Range: Between 3 seconds and the value in the Max advertise interval. Default: 0.75 times the value in the Max advertise interval.
Max. Advertise Interval	The maximum time (in seconds) allowed between sending unsolicited broadcast or multicast ICMP Router advertisements on the interface. Range: 4-1800 Default: 600
Advertisement Lifetime	The lifetime (in seconds) of the advertisements sent from the interface. Range: Max. Advertise Interval-9000 Default: 3 x Max. Advertise Interval
Advertise	Whether the address should be advertised in the Router Advertisement packets. This applies to each address on the interface and not to the interface itself. Default: Selected
Eligibility	You can make an IP address ineligible as a default router address. A router address that is not to be used as a default router has a Preference of 0. Options: Eligible/ineligible Default: Eligible.
Preference	The level of preference of the IP address as a default router address, relative to other router addresses on the same subnet. The minimum value corresponds to Ineligible and indicates that the address is not to be used as a default router. Range: 0 (Ineligible)-2147483648 (2^31) Default is 0

Configuring Router Discovery - CLI (rdisc)

ICMP Router Discovery Interfaces

Use the following commands to configure router discovery properties for specific interfaces.

set rdisc interface if_name

	<on | off>

	min‑adv‑interval <3‑1800>

	min‑adv‑interval default

	max‑adv‑interval <4‑1800>

	max‑adv‑interval default

	adv‑lifetime integer

	adv‑lifetime default

	advertise ip_address <on | off>

	advertise ip_address preference ineligible

	advertise ip_address preference integer

Parameter	Description
`<on \| off>`	Whether to run ICMP router discovery on the interface.
`min‑adv‑interval <3‑1800>`	The minimum time (in seconds) allowed between sending unsolicited broadcast or multicast ICMP router advertisements on the interface.
`min‑adv‑interval default`	A value of 450 seconds.
`max‑adv‑interval <4‑1800>`	The maximum time (in seconds) allowed between sending unsolicited broadcast or multicast ICMP router advertisements on the interface.
`max‑adv‑interval default`	A value of 600 seconds.
`adv‑lifetime integer`	The lifetime (in seconds) of the advertisements sent from the interface. An integer value between the configured value for the maximum advertisement interval and 9000.
`adv‑lifetime default`	A value of 1800 or 3 times the maximum advertisement interval.
`advertise ip_address <on \| off>`	Whether to advertise the specified IP address that is associated with the interface should be advertised in router advertisement packets.
`advertise ip_address preference ineligible`	Do not use the specified IP address as a default router.
`advertise ip_address preference integer`	The preferability of the specified IP address as a default router address relative to other router addresses on the same subnet.

ICMP Router Discovery Show Commands

Use the following commands to monitor and troubleshoot your ICMP router discovery implementation.

show rdisc

	interfaces

	interface if_name

	stats

	summary

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