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Old 02-04-2016, 04:45 PM   #1
DaijoubuKun
LQ Newbie
 
Registered: Jul 2005
Distribution: Slackware 13.37/14.0 + 64 14.0/14.1
Posts: 13

Rep: Reputation: 1
DHCP sometimes doesn't update DNS


Hi All, I'm having a strange issues with my DHCP/DNS server. I'm running Debian 7 (Wheezy) with ISC's DHCP Server and Bind9. The issue here is that some hosts perform a DHCPREQUEST, then I get a DHCPACK, but no updates for DNS. This seems to happen more with systems running systemd, but I don't believe that is the issue since some Windows hosts do it as well.

For example, I see something like this in my logs:
Code:
Feb  4 11:21:06 seadns dhcpd: DHCPREQUEST for 10.90.20.71 from 44:39:c4:5b:46:90 (dell-M6800) via eth0
Feb  4 11:21:06 seadns dhcpd: DHCPACK on 10.90.20.71 to 44:39:c4:5b:46:90 (dell-M6800) via eth0
When I only get these lines, DHCP doesn't send anything to the DNS server. However, other host will do this, which works:
Code:
Feb  4 13:34:23 seadns dhcpd: DHCPDISCOVER from dc:9f:db:45:cd:a2 via eth0
Feb  4 13:34:23 seadns dhcpd: DHCPOFFER on 10.90.10.10 to dc:9f:db:45:cd:a2 via eth0
Feb  4 13:34:23 seadns dhcpd: uid lease 10.90.20.66 for client dc:9f:db:45:cd:a2 is duplicate on 10.90.0.0/16
Feb  4 13:34:23 seadns dhcpd: DHCPREQUEST for 10.90.10.10 (10.90.10.2) from dc:9f:db:45:cd:a2 via eth0
Feb  4 13:34:23 seadns dhcpd: DHCPACK on 10.90.10.10 to dc:9f:db:85:cd:a2 via eth0
Feb  4 13:34:23 seadns named[19143]: client 127.0.0.1#29808: signer "rndc-key" approved
Feb  4 13:34:23 seadns named[19143]: client 127.0.0.1#29808: updating zone 'local.domain/IN': deleting rrset at 'mFi-mPower-84CDA2.local.domain' TXT
Feb  4 13:34:23 seadns named[19143]: client 127.0.0.1#29808: updating zone 'local.domain/IN': adding an RR at 'mFi-mPower-84CDA2.local.domain' TXT
Feb  4 13:34:23 seadns named[19143]: client 127.0.0.1#29808: updating zone 'local.domain/IN': deleting rrset at 'mFi-mPower-84CDA2.local.domain' A
Feb  4 13:34:23 seadns named[19143]: client 127.0.0.1#29808: updating zone 'local.domain/IN': adding an RR at 'mFi-mPower-84CDA2.local.domain' A
Feb  4 13:34:23 seadns dhcpd: Added new forward map from mFi-mPower-84CDA2.local.domain. to 10.90.10.10
Feb  4 13:34:23 seadns named[19143]: client 127.0.0.1#29808: signer "rndc-key" approved
Feb  4 13:34:23 seadns named[19143]: client 127.0.0.1#29808: updating zone 'in-addr.arpa/IN': deleting rrset at '10.10.90.10.in-addr.arpa' PTR
Feb  4 13:34:23 seadns named[19143]: client 127.0.0.1#29808: updating zone 'in-addr.arpa/IN': adding an RR at '10.10.90.10.in-addr.arpa' PTR
Feb  4 13:34:23 seadns dhcpd: Added reverse map from 10.10.90.10.in-addr.arpa. to mFi-mPower-84CDA2.local.domain.
As you can see, it works fine. I believe this is because I first get DHCPDISCOVER and DHCPOFFER. So I guess the over all question would be, how do I get the DHCP server to push updates to DNS(Bind9) upon either DHCPREQUEST or DHCPACK?

Thanks,

DHCP config snipit
Code:
ddns-updates on;
ddns-update-style interim;
update-static-leases on;
authoritative;
key rndc-key { algorithm hmac-md5; secret 'xxxxxx';}
allow unknown-clients;
use-host-decl-names on;
# stop windows from requesting IP every 5 minutes
option wpad code 252 = text;
option wpad "\n";
# end
update-conflict-detection false;

#
one-lease-per-client on;
update-optimization on;
deny client-updates;
#

subnet 10.90.0.0 netmask 255.255.0.0 {
        # default gateway
        option routers 10.90.10.1;
        option subnet-mask 255.255.0.0;
        option domain-name "local.domain";
        option domain-name-servers 10.90.10.2;
        range 10.90.20.3 10.90.20.90;
        #range dynamic-bootp 10.90.20.3 10.90.20.90;
#        default-lease-time 86400;
        default-lease-time 3600;
#        max-lease-time 604800;
        max-lease-time 7200;
        ddns-domainname "local.domain.";
        ddns-rev-domainname "in-addr.arpa.";
}
 
Old 02-05-2016, 03:27 AM   #2
MrTux
Member
 
Registered: Dec 2015
Posts: 131

Rep: Reputation: Disabled
why do you want to make a DNS server use DHCP?

Wouldn't it be easier to add multiple DNS servers to your config on your DNS server and make it static or create a reservation?
 
Old 02-05-2016, 12:30 PM   #3
DaijoubuKun
LQ Newbie
 
Registered: Jul 2005
Distribution: Slackware 13.37/14.0 + 64 14.0/14.1
Posts: 13

Original Poster
Rep: Reputation: 1
I want dynamics DNS for the network. Multiple DNS servers will not solve this issue.

I use ddns so I can access devices/hosts by name instead of IP. While most systems have static leases (like servers and printers), some do not, and can't since they will often times move between vlans.
 
  


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