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ICMPv6 Router Advertisement and Router Solicitation Messages
(Page 3 of 3)
ICMPv6 Router Solicitation Message Format
The format of an ICMPv6 Router Solicitation message is as shown Table 110 and Figure 159.
Field Name |
Size (bytes) |
Description |
Type |
1 |
Type: Identifies the ICMPv6 message type; for Router Solicitation messages the value is 133. |
Code |
1 |
Code: Not used; set to 0. |
Checksum |
2 |
Checksum: 16-bit checksum field for the ICMP header, as described in the topic on the ICMP common message format. |
Reserved |
4 |
Reserved: 4 reserved bytes set to 0. |
Options |
Variable |
Options: If the device sending the Router Solicitation knows its layer two address, it should be included in a Source Link-Layer Address option. Option formats are described in a separate topic. |
Router Solicitation messages are normally sent to the IPv6 “all routers” multicast address; this is the most efficient method since routers are required to subscribe to this multicast address while hosts will ignore it. A routine (unsolicited) Router Advertisement is sent to all devices using the “all nodes” multicast address for the local network. A Router Advertisement that is sent in response to a Router Solicitation goes unicast back to the device that sent the solicitation.
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Key Concept: ICMPv6 Router Advertisement messages are sent regularly by IPv6 routers to inform hosts of their presence and characteristics, and to provide hosts with parameters they need to function properly on the local network. A host that wants to find out immediately what routers are present may send a Router Solicitation, which will prompt listening routers to send out Router Advertisements.
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