[Dnsmasq-discuss] Need help configuring dhcp stateful IPv6

Simon Kelley simon at thekelleys.org.uk
Fri May 18 10:10:16 BST 2012

On 18/05/12 09:59, Andre Coetzee wrote:
> Hello
> I've installed dnsmasq 2.61 on an x86 computer on my LAN. DNS is working
> fine for A, AAAA, CNAME and PTR records. DHCP for IPv4 is also working.
> I have recently began to dabble with IPv6 on my LAN and since I do not
> yet have a provider for IPv6, I have decided to use RFC 4193 Unique
> Local (fdxx:) addresses for my LAN. Since I only have a few machines, I
> chose a subnet prefix of /123 and using static IPv6 configuration I was
> able to ping6 other machines on the same subnet (even by their names),
> as well as from one subnet to another, even using a sit tunnel.
> When I set my dhcp-range option in dnsmasq.conf with a prefix-length of
> 123, I get an "inconsistent DHCPv6 range" error. setting this value to
> 125 or greater seems to work, also setting it to 120 or less seems to be
> acceptable to dnsmasq. Checking out my range with an ip calculator
> didn't reveal any errors (my dynamic ip range is within the same 5-bit
> subnet).
> These are the pertinent bits of my current conf file:
> dhcp-range=interface:eth0, fdxx:xxxx:xxxx::10, fdxx:xxxx:xxxx::1f, 120, 4h
> enable-ra
> log-dhcp
> dhcp-sequential-ip
> When I enable networking on a client machine (linux), I see
> "RTR-SOLICIT(eth0)" messages in the logs, but no responses or
> advertisements coming from the dnsmasq machine.
> I have enabled IPv6 forwarding:
> # cat /proc/sys/net/ipv6/conf/all/forwarding 
> 1
> Please can someone indicate what else I need to check? (I tried using a
> /64 prefix also, but the results were the same).

OK, first thing, your post took me straight to an embarrassing bug: it's
all broken if the prefix length is NOT divisible by 8 - all bets are off
in that case.

Since you can't get it to work even with prefix-length=64, there must be
something else going on. How is the relevant interface configured? The
prefix length there must  match that configured into dnsmasq.



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