DHCP Lease Time - 150s

Colantuoni, Robert rgc at buffalo.edu
Wed May 26 15:48:38 UTC 2010


Glenn,

Thank you!

Yes it looks like MCLT is set to 150. I hadn't caught this b/c it's in a file that doesn't change. I recall that it should be less than the lease time correct?  If I'm handing out either a 5 min lease or 7 day lease, would it be appropriate to do 5 minutes?


----------------------------------
Robert G Colantuoni
CIT - Operational Support Services
University at Buffalo
rgc at buffalo.edu
716.645.3552



> -----Original Message-----
> From: dhcp-users-bounces+rgc=buffalo.edu at lists.isc.org [mailto:dhcp-users-
> bounces+rgc=buffalo.edu at lists.isc.org] On Behalf Of Glenn Satchell
> Sent: Wednesday, May 26, 2010 11:43 AM
> To: Users of ISC DHCP
> Subject: Re: DHCP Lease Time - 150s
> 
> Hi ROb
> 
> What is mclt set to in the primary failover configuration?
> 
> mclt is used as an initial lease time to offer clients in a failover
> configuration. If the client accepts the lease then the server transfers
> this information to the partner and offers the requested lease time the
> next time the client renews.
> 
> 150 is probably a bit low, so something like in the range 5 to 30
> minutes might be better, although setting this to the best value is a
> bit of a black art.
> 
> regards,
> -glenn
> 
> On 05/27/10 01:31, Colantuoni, Robert wrote:
> > I have an issue with short lease times being issued, mostly with Cisco VoIP
> phones. We have a pretty vanilla config, using failover, that boots known
> hosts from one pool of addresses and unknown hosts from another pool. We also
> hand out different lease times for known and unknown hosts.
> >
> > ISC DHCP 4.0.0
> >
> > Relevant Config Sections:
> >
> > -- cut --
> >
> > # LEASE OPTIONS - GLOBAL
> > default-lease-time 604800;      #  7 days.
> > max-lease-time 1209600;         #  14 days.
> > min-lease-time 604800;          #  7 days.
> >
> > -- cut --
> >
> > if not known {
> >          default-lease-time 300;         #  5 minutes
> >          max-lease-time 300;             #  5 minutes
> >          min-lease-time 300;             #  5 minutes
> > }
> >
> > -- cut --
> >
> > class "active"   {
> >          match hardware;
> >          default-lease-time 604800;      #  7 days.
> >          max-lease-time 1209600;         # 14 days.
> >          min-lease-time 604800;          #  7 days.
> > 	 -- cut --
> > }
> >
> > We then declare all hosts we know about like this:
> >
> > subclass "active" 1:00:1e:f7:c2:3e:7e;
> > host voip-6222 {
> >       hardware ethernet 00:1e:f7:c2:3e:7e;
> >       -- cut --
> > }
> >
> > This has worked well for us for many years, but I've recently seen an issue
> crop up where the DHCP server is handing out leases of 150 seconds to known
> hosts that should be receiving 7 day leases.  I thought perhaps this was
> related to the 300s default above, so I changed it to 400s but the short
> lease time didn't increase relatively to 200s.
> >
> > There is nowhere in my config that specifies anything like 150 seconds for
> a lease! I'm pretty sure the defaults are higher than that also. I've grepped
> through the source and I didn't see anything obvious. Even more puzzling is
> that the tstp (the date the DHCP server tells it's failover peer that the
> lease expires) is correctly 7 days:
> >
> > lease 10.7.6.61 {
> >    starts 3 2010/05/26 14:31:33;
> >    ends 3 2010/05/26 14:34:03;
> >    tstp 3 2010/06/02 14:32:48;
> >    tsfp 3 2010/06/02 14:32:48;
> >    atsfp 3 2010/06/02 14:32:48;
> >    cltt 3 2010/05/26 14:31:33;
> >    binding state active;
> >    next binding state expired;
> >    hardware ethernet 9c:af:ca:ff:ca:95;
> >    -- cut --
> > }
> >
> > The phones seem to eventually get a 7 day lease, but it's intermittent.
> >
> > I hope the email provides enough detail... Thanks in advance,
> >
> > Rob
> >
> >
> >
> > ----------------------------------
> > Robert G Colantuoni
> > CIT - Operational Support Services
> > University at Buffalo
> > rgc at buffalo.edu
> > 716.645.3552
> >
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