DDNS Updates on lease expire.

[Mark Mc Nicholas]

Hi Simon,
Thanks for pointing that out,
That is an artifact of some late night troubleshooting :)
Kind Regards
Mark

On Wed, Aug 17, 2016 at 1:54 PM, Simon Hobson <dhcp1 at thehobsons.co.uk>
wrote:

> Mark Mc Nicholas <markmcn at section9.ie> wrote:
>
> > Below are the config's of DHCPD & Bind,
>
>
> > ====DHCPD Config====
> >
> > ddns-updates on;
> > ddns-update-style interim;
> > update-static-leases    on;
> > key sun-key { algorithm hmac-md5; secret "123456789";}
> > allow unknown-clients;
> > use-host-decl-names on;
> >
> > zone    i.home.ie.{
> >         primary moto.i.home.ie;
> >         key sun-key;
> > }
> >
> > # Common to all subnets
> > option domain-name "home.ie";
> > default-lease-time 1800;
> > max-lease-time 14400;
> > authoritative;
> > allow unknown-clients;
> >
> > subnet 172.17.2.0 netmask 255.255.255.128 {
> >         range 172.17.2.41 172.17.2.100;
> >         default-lease-time 1800;
> >         max-lease-time 14400;
> >         authoritative;
> >         option routers 172.17.2.1;
> >         option domain-name-servers 172.17.2.4,192.168.252.1 ;
> >         option domain-name "i.home.ie";
> >         option domain-search "i.home.ie";
> >         option ntp-servers 193.1.219.116,193.1.31.66;
> >         ddns-domainname "i.home.ie.";
> >         ddns-rev-domainname "in-addr.arpa.";
> >
> >         host skynet09{
> >                 hardware ethernet AC:CF:23:8D:10:60;
> >                 fixed-address 172.17.2.39;
> >                 ddns-hostname "skynet009";
> >         }
> > }
>
> The first thing to note is that you have a host declaration within a
> subnet. Host declarations are always global in scope, but do have
> inheritance - this can cause some "interesting" effects if the client pops
> up on another subnet. So, while it's not directly relevant to the problem
> you are enquiring about - put your host declarations in the global scope
> and save yourself some pain later on ;-)
>
>
>
> > Bind Logs of an Update
> >
> > named[1563]: client 172.17.2.4#28949: updating zone 'i.home.ie/IN':
> update unsuccessful: skynet001.i.home.ie: 'name not in use' prerequisite
> not satisfied (YXDOMAIN)
> > named[1563]: client 172.17.2.4#28949: signer "sun-key" approved
> > named[1563]: client 172.17.2.4#28949: updating zone 'i.home.ie/IN':
> deleting rrset at 'skynet001.i.home.ie' A
> > named[1563]: client 172.17.2.4#28949: updating zone 'i.home.ie/IN':
> adding an RR at 'skynet001.i.home.ie' A
> > named[1563]: client 172.17.2.4#28949: signer "sun-key" approved
> >
> > DHCP Logs for the same device
> > dhcpd[6271]: DHCPREQUEST for 172.17.2.31 from ac:cf:23:8d:77:56 via eth0
> > dhcpd[6271]: DHCPACK on 172.17.2.31 to ac:cf:23:8d:77:56 via eth0
> > dhcpd[6271]: Added new forward map from skynet001.i.home.ie. to
> 172.17.2.31
> > dhcpd[6271]: Added reverse map from 31.2.17.172.in-addr.arpa. to
> skynet001.i.home.ie.
>
> OK, that's all normal.
> But, I see 172.17.2.31 is not in the range (172.17.2.41 to 172.17.2.100)
> defined for dynamic clients, so I'm guessing that you have trimmed out a
> host declaration for skynet001 ? If so, then the answer is simple - DNS
> entries for these hosts are not automatically removed, because there is no
> mechanism to do so.
>
> More detail on that.
> When a host gets a lease from a static address assignment in a host
> declaration, there is no lease created by the server to go with it. Because
> it's a static assignment, there's no need to track it, and so there's a
> shortcut where from the client PoV it gets a lease, but the server doesn't
> bother recording it.
> As there is no lease recorded by the server, there's nothing to expire,
> and so nothing to trigger removal of the corresponding DDNS entries.
> Also, without the "update-static-leases on;" statement, you also would not
> get DNS updates on "lease" issue.
>
> If you need DDNS updates to remove the entries, then you'll have to use
> "real" leases. You can get much the same effect by creating a "reserved"
> lease. You can do this (AIUI) on a running server via OMAPI, or after
> stopping the server you can do it by editing the leases file to add/edit a
> lease with the "Reserved" keyword.
> A reserved lease acts just like any other dynamic lease (gets issued,
> renewed, expires, etc) except that it will never be re-assigned to another
> client.
>
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>



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