Router Solicitation
ICMP Type 10 Router Solicitation is sent by a host to request immediate Router Advertisement messages from all routers on the subnet. Instead of waiting for a periodic advertisement, a host that just joined the network sends a solicitation to discover available routers immediately.
Description
When a host initializes its network interface, it may send an ICMP Router Solicitation to the all-routers multicast address (224.0.0.2) or broadcast address to request immediate Router Advertisements rather than waiting for the next periodic advertisement interval.
Routers on the subnet respond with Router Advertisement messages (Type 9) within a few seconds. This reduces the time a newly connected host must wait to discover its default gateway from the advertisement interval (typically 7-10 minutes) to a few seconds.
ICMP Router Discovery including Type 10 is specified in RFC 1256. In IPv6, the equivalent is NDP Router Solicitation (ICMPv6 Type 133), which works on the same principle but with a different wire format.
Common Causes
- –Host initializing network interface and requesting gateway discovery
- –Host waking from sleep or reconnecting to network
- –Network interface restart triggering gateway rediscovery