[Dnsmasq-discuss] Confusion about "no address range available for DHCPv6 request via ..."

[Daniel Farina]

Hello everyone,

I have been trying to set up an IPv6-only network for a virtual machine
with route advertisements and DHCP configuration. I've had some success,
but I have a question.

I have a dnsmasq.conf that looks like this, to delegate a /80 chunk of a
/64 network to a virtual machine:

interface=tapvm4qyj3a
enable-ra
dhcp-authoritative
leasefile-ro
ra-param=tapvm4qyj3a,mtu:1280,high,60,1200
dhcp-range=2a01:4f9:2b:35a:7df2::2,2a01:4f9:2b:35a:7df2::2,80

If I have an address configuration like this on the host outside the
virtual machine, it works well:

3: tapvm4qyj3a: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel
state UP group default qlen 1000
    link/ether 82:d6:93:69:72:82 brd ff:ff:ff:ff:ff:ff
    inet6 2a01:4f9:2b:35a:7df2::1/80 scope global
       valid_lft forever preferred_lft forever
    inet6 fe80::80d6:93ff:fe69:7282/64 scope link
       valid_lft forever preferred_lft forever

The thing I find dissatisfying about this is that the VM is not able to
listen on 2a01:4f9:2b:35a:7df2::1 anymore once I've done this, is my
understanding: the host will process the traffic, right? If I remove the
address on the guest's network, dnsmasq warns me repeatedly, and does not
work:

ip addr del 2a01:4f9:2b:35a:7df2::1/80  dev tapvm4qyj3a

dnsmasq-dhcp: no address range available for DHCPv6 request via tapvm4qyj3a
dnsmasq-dhcp: no address range available for DHCPv6 request via tapvm4qyj3a
dnsmasq-dhcp: no address range available for DHCPv6 request via tapvm4qyj3a
...

My question is partially that of norms: is it normal to squat on a bit of
the guest's address space like this? Is there a preferred way that avoids
this, or does something different still? I know that a number of non-SLAAC
configurations tend to sit on ::2 as the first unicast address, is this
related to the reason why?

I will be expanding my use of dnsmasq to DNS, so this may figure in the
answer.

Thank you for considering my question.
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