Expiring leases

Glenn Satchell Glenn.Satchell at uniq.com.au
Tue Mar 25 11:27:28 UTC 2008

If you're using a class like this to match PXE clients, then turn off
dynamic dns updates for the pxe addresses:

class "pxe-clients" {
 match if substring (option vendor-class-identifier, 0, 9)="PXEClient";
 next-server tftpserver;
 # turn off dynamic dns updates for PXE addresses
 ddns-updates off;

If you do need DNS entries for PXE hosts, then put them in a different
domain by setting option server.ddns-domainname to a different
domainname (maybe pxe.yourdomain.com) in the class.


>Subject: RE: Expiring leases
>Date: Tue, 25 Mar 2008 10:37:34 +1100
>From: "Lowrie, Paul" <paul.lowrie at nz.unisys.com>
>To: <dhcp-users at isc.org>
>Hi Damian,
>Yes - Ive had this problem (and still working on a solution). it goes
>like this.
>Two servers in failover pair and a  PC with PXEboot still enabled.
>   PXEboot request from PC is given address "ABCD" by "Server-1"
>   Server-1 puts PC=ABCD and ABCD=PC into DNS
>   PC keeps booting....
>   OS Boot request from PC is given "EFGH"  by "Server-2"
>   DHCP has "one_lease_per_client on;"...
>   Server 2 tells  Server-1 that  PC now= EFGH,   so
>   Server-1 removes the entries given for "PC=ABCD" and :"ABCD=PC" from
>the DNS.
>    End result - PC has a valid lease and there is nothing in the DNS -
>Crux is that this isnt considered a fault as according to "the
>specficiations" and other dialogue in this mail list this is a design
>    The OS-boot boot packet is sent with a client-identifier
>    The PXEboot packet is sent without this identifier,
>Therefore "according to the specification" these are different NIC's so
>should be given different leases
>Cheers  & Good Luck
> All,
>Setup: two peered servers.
>Problem: occasional lost of dns data due to lease expiration.
>Looks like workstation omits T1 and T2 communication, and renews its
>lease at T3. Well, one peer adds dns data. The other find the lease
>expired and removes dns data a split second after the lease was granted.
>Anybody with similar problem? Any help would be appreciated!
>Log snips:
>Mar  3 08:28:57 s_sys at tlpgbrdns-2.edj.ad.edwardjones.com dhcpd: Added
>new forward map from USU41602D1.b22838.branches.edwardjones.com to
>Mar  3 08:28:57 s_sys at nlpgbrdns-1.edj.ad.edwardjones.com dhcpd: if
>USU41602D1.b22838.branches.edwardjones.com IN TXT
>"312e461c3d4bf095111c87d30e4f30e7f2" rrset exists and
>USU41602D1.b22838.branches.edwardjones.com IN A rrset
>exists delete USU41602D1.b22838.branches.edwardjones.com IN A
> success.
>Damjan Stulic
>IS Security Identity Management
>Edward Jones
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