This type of message therefore has a standard length of 128 bits, with additional bits for options. Valid options include the routers’ MAC address, the ‘Maximum Transmission Unit’ and all relevant prefix information.
The ‘type’ field is set to 134 and the ‘code’ field are always set to 0. That is followed by a 16-bit ICMP checksum and an 8-bit length specification of the hop limit, which may include the stations recommended by the router.
After that follow single bits, which provide insight into:
- Whether IP addresses can be obtained via dynamic DHCPv6 (M)
- And whether other address information can be obtained via dynamic DHCPv6 (O).
The ‘reserved’ field remains unused and is ignored by the recipient. In addition, the router advertisement contains figures about:
- The time in seconds that the router should remain in the default router list (router lifespan, 16-bit integer, maximum 65535).
- The time in milliseconds that an address in the neighbor cache should still be available after reaching availability (availability time-out, 32-bit integer, maximum of approximately 50 days).
- The time in milliseconds after which a neighbor solicitation message (see below) should be resent (resolution time-out, 32-bit integer).