[Dnsmasq-discuss] DHCPv6 and prefix length on clients

[Niels Penneman]

Thank you for the quick reply.

I have added 'enable-ra' to my dnsmasq configuration, which I believe
sends out router advertisements with A bit off and M bit set.

My IPv6 configuration for the dnsmasq VM (in NetworkManager) is set to
fdaa:aaaa:aaaa::2/64; with 'ip -6 addr' I get:

inet6 fdaa:aaaa:aaaa::2/64 scope global
valid_lft forever preferred_lft forever

The other VM now receives an IPv6 address fdaa:aaaa:aaaa::<random> from
dnsmasq; using 'ip -6 addr' I get:

inet6 fdaa:aaaa:aaaa::<random>/64 scope global dynamic
valid_lft <time> preferred_lft <time>

If IPv6 addresses have no prefix, why do I have to set '/64' in the
network configuration of my dnsmasq VM for dnsmasq to work? Setting /128
there causes dnsmasq to complain that 'no addresses are available'.
Furthermore, both VMs are still not able to reach each other: the VM
that dynamically receives its IPv6 address never configures an
appropriate route.


Regards,

Niels

On 07/19/2014 05:09 PM, Roy Marples wrote:
> On 2014-07-19 15:53, Niels Penneman wrote:
>> ... but it has a prefix length of 128. Hence, the VMs cannot see each
>> other.
>>
>> My configuration explicitly specifies a prefix length of 64; what could
>> cause the prefix length to be set to 128 on the DHCPv6 client side?
> 
> DHCPv6 addresses have no prefix length, they are just an address, so
> always a /128.
> What you need to do is advertise a /64 prefix, but with the M bit set
> and the AUTOCONF bit disabled.
> 
> That way the hosts you want off the IPv6 network will be aware of the
> prefix, but won't have a global address on it.
> 
> Roy



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