running a DHCPv6 server to provide only DNS servers

psycroptic · 08-16-2015, 12:05 AM

I have noticed that Windows clients will not auto-configure IPv6 DNS servers via the RDNSS capability of RA messages. I am considering setting up a DHCPv6 server on my LAN that will provide just DNS records to clients. Are there any pitfalls to this, or things to be concerned about?

smallpond · 08-16-2015, 07:00 AM

Slaac + stateless dhcp should work if your router advertisements set M=0 and O=1.

psycroptic · 08-17-2015, 01:21 AM

Alright thanks.

So I'm using the ISC DHCP server on an Arch Linux machine currently to hand out IPv4 addresses. The Arch machine is also a DNS server. My router is handing out global IPv6 addresses to LAN clients. I would like the DHCP server to only provide a DNS server address which will be the link-local of the Arch machine. From reading docs, I believe I can add the following to /etc/dhcpd.conf:

Code:

subnet6 fe80::/64 {
    option dhcp6.name-servers fe80::aa:bb:cc:dd;
}

Where fe80::aa:bb:cc:dd is the IPv6 link-local address of the Arch machine.... or no?

smallpond · 08-17-2015, 09:02 AM

Yes. You can also push a domain if you want, like:

Code:

option dhcp6.domain-search "assimilateb.org";

psycroptic · 08-17-2015, 11:56 PM

So here's what my /etc/dhcpd6.conf looks like:

Code:

default-lease-time 7200;
max-lease-time 7200;
log-facility local7;
subnet6 fe80::/64 {
        option dhcp6.name-servers fe80::SERVER-LINKLOCAL;
}

When clients try to request a lease (on Windows by running "ipconfig /renew6"), I get the following error entry in journald:

Code:

Aug 17 23:51:41 SERVER dhcpd[18708]: Solicit message from fe80::CLIENT-IPV6-LINKLOCAL port 546, transaction ID 0x225ADE00
Aug 17 23:51:41 SERVER dhcpd[18708]: Unable to pick client address: no IPv6 pools on this shared network
Aug 17 23:51:41 SERVER dhcpd[18708]: Sending Advertise to fe80::CLIENT-IPV6-LINKLOCAL port 546

Any ideas?