Comment 10 for bug 1609898

Dan Streetman (ddstreet) wrote :

> In what circumstances do dhcpv6 servers hand out an IPv6 address without also reporting
> the prefix length the client should use? Something seems wrong here. (Is it me? :)

unfortunately the dhcpv6 spec (RFC 3315) doesn't provide a way for a dhcpv6 server to tell a client what the address's prefix length is. It just provides the address.

Router Advertisement messages do provide prefix length, but that's a different protocol from dhcpv6; sometimes dhcpv6 and RA are provided by a server, and sometimes only one of dhcpv6 or RA are provided.

RA allows clients to "auto" generate ipv6 addresses, inside the prefix length. dhcpv6 provides specific ipv6 addresses to clients, but doesn't tell them the prefix length. Clients don't need the prefix length if they are assigned the full ipv6 address, because they can find other on-link ipv6 addresses using Neighbor Discovery, and dhcpv6 does provide its link-local server address (to use as a default route).