ipv6 dhcp server not handing out addresses

Sten Carlsen stenc at s-carlsen.dk
Thu Nov 16 16:22:59 UTC 2017

On 16/11/2017 17:05, robert at spotswood-computer.net wrote:
> I've trying to retire an old Debian server (v7 Wheezy). I've new one built
> (really a VM) and installed (v9 - Stretch). One by one, I'm moving the
> services over. Going well, until I hit the IPv6 dhcp server. The ipv4 dhcp
> server went smooth.
> The old server is running isc-dhcp-server 4.2.2, while the new server is
> running isc-dhcp-server 4.3.5.
> I copied the configuration file, but not the lease database from old
> server. Then I stopped the old ipv6 (and ipv4) dhcp servers and started
> the new ones. The ipv6 dhcp server starts, and is listening, but it is not
> handing out addresses. I tested with two Windows machine: ipconfig
> /release6 then ipconfig /renew6. Both machines had an ipv6 address from
> the old dhcp server, so it's not a client problem, and can renew said
> address.
> Out of frustration, I copied the old database to the new server and
> restarted. Still not working.
> I finally fired up wireshark on the client, and the problem seems to be
> there are no advertise reply to the solicit from the client, which does
> show up in the dhcpd logs. So the server sees the request, but doesn't
> answer it.
> I checked the ip6tables and everything is accept, so it's not a firewall
> issue. Any ideas?
You may want to try Wireshark on the server to see if the request
actually gets there.
Could be an issue with switches along the way. I had an issue with a
switch that was set to prevent DDOS attacks and blocked packets with
identical source and destination ports. Removing that check made a lot
of things work again.
> == config file ==
> default-lease-time 6048;
> max-lease-time 6048;
> log-facility local7;
> ddns-updates on;
> ddns-update-style interim;
> update-static-leases on;
> authoritative;
> #log-facility debug;
> subnet6 fd00:220:0:1::/64 {
> 	#Range for clients
> 	range6 fd00:220:0:1::601 fd00:220:0:1::800;
> 	#Additional options
> 	option dhcp6.name-servers fd00:220:0:1::40, fd00:220:0:1::50;
> 	option dhcp6.domain-search "redacted.name";
> }
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Best regards

Sten Carlsen

No improvements come from shouting:


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