Routers use the IPv4 ICMP Router Discovery Protocol to announce their presence to other systems in the subnet. Hosts use the protocol to dynamically discover IPv4 routers in the same subnet.
IPv4 ICMP Router Discovery Protocol (IRDP) has two components: ICMP router advertisement and ICMP solicitation request.
In SLX, both components of the protocol are disabled by default on Layer 3 interfaces. Use the ip irdp command to enable the components at the interface level.
Routers are designed to periodically send unsolicited router advertisements through all Layer 3 interfaces. In SLX, the all-system multicast IP address, 224.0.0.1, is used as the destination IP address.
Only one advertisement packet (an ICMP packet) is sent, regardless of the number of IP addresses configured on the interface. The packet contains a list of all configured IP addresses.
| Parameter | Value |
|---|---|
|
Maximum advertisement interval The maximum frequency with which advertisements are sent. For example, once every 600 seconds. |
600 seconds |
|
Minimum advertisement interval The minimum frequency with which advertisements are sent. For example, once every 450 seconds. |
450 seconds |
|
Lifetime The maximum length of time that advertised addresses are considered valid router addresses. |
1800 seconds |
A router advertisement includes a "preference level" for each advertised router address. A host chooses router addresses based on the preference level. In SLX, the default preference level is 0. You cannot change it.
A host sends a solicitation request to determine the presence of a router. The request triggers a router advertisement response from the routers on the same subnet. The routers respond to solicitation requests that arrive on the all-router multicast IP address, 224.0.0.2.
Routers can discard solicitation requests from invalid source IP addresses.