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IOS DHCP lease time corresponds with phones unregistering

mmedwid
Level 3
Level 3

‎03-04-2011 04:52 PM - edited ‎03-16-2019 03:48 AM

I have finally found a solid correlation to explain why some phone reboot at one of my sites. 

If I find the time that a phone unregisterd from the UCM 7.1 server and then look at the

DHCP lease table - the lease expiry is inevitably five minutes before the unregistration. 

I toss this out in case anyone else has seen this.  The fix should be to simply change

lease times to infinite.  The bad effect was that phones would drop calls in progress while

the DHCP lease would renew.  The lease timer was at default which is 1 day.  The phones

unregistering and losing calls did not occur with every phone and the symptom could

randomly affect any particular phone. 

Should I report this as a bug?  If so - how?

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2 Replies 2

Jonathan Schulenberg
Hall of Fame
Hall of Fame

‎03-04-2011 08:19 PM

Have you performed a packet capture or reviewed the DHCP server logs to understand why the server is not providing a renewal to the phone? The phone makes a renewal request when 50% of the lease time remains. It should never get to the expiry threshold - and then totally release the address - unless the DHCP server has been denying the renewal request.

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mmedwid
Level 3
Level 3
In response to Jonathan Schulenberg

‎03-04-2011 08:51 PM

I caught a little big of event debug as you can see below.  But my main priority is to get this fixed.  So as soon as I verified the correlation I changed the lease to infinite. The config is below too. 

no ip dhcp use vrf connected

ip dhcp excluded-address 10.10.65.1 10.10.65.40

!

ip dhcp pool Phones

   network 10.10.65.0 255.255.255.0

   option 150 ip 10.10.10.72

   default-router 10.10.65.1

   dns-server 10.10.25.25 10.10.101.139

   domain-name xyz.com

010352: Mar  4 22:41:47.536: DHCPD: checking for expired leases.

010353: Mar  4 22:43:13.892: DHCPD: Sending notification of ASSIGNMENT:

010354: Mar  4 22:43:13.892:  DHCPD: address 10.10.65.52 mask 255.255.255.0

010355: Mar  4 22:43:13.896:   DHCPD: htype 1 chaddr 6c50.4d57.049f

010356: Mar  4 22:43:13.896:   DHCPD: lease time remaining (secs) = 86400

now it looks like..

012271: Mar  5 04:39:47.618: DHCPD: checking for expired leases.

012272: Mar  5 04:40:27.414: DHCPD: Sending notification of ASSIGNMENT:

012273: Mar  5 04:40:27.414:  DHCPD: address 10.10.65.77 mask 255.255.255.0

012274: Mar  5 04:40:27.414:   DHCPD: htype 1 chaddr e804.6212.75b7

012275: Mar  5 04:40:27.414:   DHCPD: lease time remaining (secs) = 4294967295

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