[Dnsmasq-discuss] IPv6 dhcp-range prefix-len only /64?

Denis KOTOV evengard at trioptimum.com
Wed May 6 18:27:37 BST 2020


Hello!

I've stumbled upon a weird problem with IPv6 DHCP with DNSMasq.
I have a /48 IPv6 prefix. For example let it be AAAA:AAAA:AAAA::
The interface on which DNSMasq receives the DHCP/RA queries is, for
example, tap0 (it's for a VPN server) with an assigned address of
AAAA:AAAA:AAAA::1/48.
Now I wanted to create a dual DHCP/SLAAC configuration, but instead of
making them both on the same prefix, I wanted to split them into
subprefixes, i.e.:
all static DHCPv6 queries would be assigned on AAAA:AAAA:AAAA:1::
all dynamic DHCPv6 queries would be assigned on AAAA:AAAA:AAAA:2::
all SLAAC configuration would be done on AAAA:AAAA:AAAA:FF00::
Each on it's own /64 prefix.
I've tried to set it up, but it seems that each time I define it like this:
dhcp-range=tap0, AAAA:AAAA:AAAA:FF00::,slaac,ra-stateless,ra-only,64 #for
SLAAC
dhcp-range=tap0, AAAA:AAAA:AAAA:2::,64,1h #for dynamic DHCPv6
I just don't get a lease at all... Which is probably logical.
When I try to specify the actual prefix of 48 instead of 64, I get the error
"prefix length must be at least 64"
even for the dynamic DHCPv6 option.
I've worked around that by assigning IPs to the tap0 interface of
AAAA:AAAA:AAAA:FF00::/64
AAAA:AAAA:AAAA:1::/64
AAAA:AAAA:AAAA:2::/64
but it really feels like a hack than a real solution.
Is there any cause why we can't set a prefix-len smaller than 64, to allow
configuring different subprefixes differently?

-Evengard
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