Isc dhcp server v6 configuration for clients through a relay

joseph orfeuil joseph.orfeuil at
Sat Sep 14 11:21:56 UTC 2013


i'm running isc-dhcp-server 4.1-ESV-R4 on ubuntu 12.04.
The NIC dhcpd is bound to is an ipv6 interface (actually dual stack but
only configured for IPv6).

My DHCP server is in network A and my point would be to serve IP addresses
to network B.
There's a router between networks A and B, acting as a dhcp relay.

Example :

Network A ==== Router ==== Network B
Let's assume Network A subnet is 2013:0:0:1::/64 and Network B subnet is
Let's also consider DHCP server address is 2013:0:0:1::bbbb/64.

My point would then be to allocate addresses belonging to prefix
Below is an example of my dhcpd6.conf (at least the way i'd like to see it

default-lease-time 600;
max-lease-time 7200;
log-facility local7;
option dhcp6.rapid-commit;
pid-file-name "/var/run/dhcp-server/";
subnet6 2013:0:0:1::/64 {
 range6 2013:dead:beef:8001::1001 2013:dead:beef:8001::1999;
prefix6 2013:0:0:100:: 2013:0:0:f00:: /56;

When running like this, when receiving a sollict request, no reply is sent
(using rapid commit that's why next step is reply) because it says "No
subnet found for link-address 2013:dead:beef:8001::"

range6 2013:0:0:1::1001 2013:0:0:1::1999; works... but then, i have clients
in network B receiving IPs from network A... which does not work.

If ever i configure an additional address 2013:dead:beef:8001::bbbb/64 on
DHCP server side, i'm then stuck as i won't be able to indicate that
2013:dead:beef:8001::/64 has to be reached through the router (actually

On the other hand, i also tried to configure the DHCP server with a subnet6
2013:dead:beef:8001::/64{}, thinking this is the actual subnet in DHCP
sollicit before it is relayed... but then the server just won't start as
there's no subnet6 declaration matching the one configured on the machine

Any help would be very much appreciated. I don't really understand why
addresses i'm attempting to allocated are verified as to be part of network
A. Is there any configuration i miss to indicate we are serving for client
behind a relay?

Thanks a lot.


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