[Dnsmasq-discuss] Unable to configure stateful prefix length larger than 64

[Pablo Rodríguez Fernández]

I found the problem.

I tried do RA with radvd and now I've got an associated route of /124,
but not the address (see below); investigating, I found that,
accordingly with RFC 4862, section 5.5.3, any prefix information without
A flag will be ignored. Still, in my case, i needed to set L (onlink)
flag, too.

> 16:54:59.202489 IP6 (class 0xc0, hlim 255, next-header ICMPv6 (58)
> payload length: 88) fe80::ba27:ebff:fe93:eafb >
> fe80::219:66ff:fe38:6cf4: [icmp6 sum ok] ICMP6, router advertisement,
> length 88
>         hop limit 64, Flags [managed, other stateful], pref medium,
> router lifetime 1800s, reachable time 0s, retrans time 0s
>           prefix info option (3), length 32 (4): fc00::10/124, Flags
> [none], valid time 7200s, pref. time 7200s
>           mtu option (5), length 8 (1):  1500
>           source link-address option (1), length 8 (1):
b8:27:eb:93:ea:fb
>           rdnss option (25), length 24 (3):  lifetime 1800s, addr:
fc00::11

As you could see in my tcpdump log, dnsmasq's RA doesn't send A (nor L)
flag, so prefix information is ignored. This could be fix if you set
slaac or ra-stateless mode; however, dnsmasq require a 64 prefix length
to use these modes, but, accordingly to section 5.5.3.d, if stateless
prefix is the same that announced prefix info (it'll actually be),
dnsmasq shouldn't require that.

As for ip address, seems that is a isc-dhcp bug, as is explained on
debian bug tracking
(http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=684009).

Sorry if i was a bit spammer.

Greetings,
Pablo