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Today's Topics:

   1. Inconsistent behaviour with a valid lease(s) in the leases'
      DB and no DHCP server up. (Tomasz Motyl)


Message: 1
Date: Tue, 16 Feb 2021 07:25:45 +0000 (UTC)
From: Tomasz Motyl <>
To: "" <>
Subject: Inconsistent behaviour with a valid lease(s) in the leases'
        DB and no DHCP server up.
Message-ID: <>
Content-Type: text/plain; charset="utf-8"

Hello All,
I ran into some interesting behaviour of the ISC DHCP client v4.4.1. It happens 
when a host boots up in a network with the DHCP server (temporarily) down and 
having at least one valid lease recorded.I had created a bug entry here: For 
the track record I had created a bug entry here: Inconsistent behaviour with a 
valid lease(s) in the leases' DB and no DHCP server up. (#162) ? Issues ? ISC 
Open Source Projects / dhcp but I shall repeat the information right below.
Client has timeout set-up to? 133[s]:
timeout 131;
retry 33;
reboot 9;
select-timeout 3;
initial-interval 2;

interface "eth1" {
  request subnet-mask, broadcast-address, time-offset, routers, domain-name, 
domain-name-servers, host-name, ntp-servers, vendor-encapsulated-options, 
dhcp-renewal-time, dhcp-rebinding-time;
  require subnet-mask;

The current date and time are: Wed 03 Feb 2021 12:33:20 PM PST
The lease entry is as follows:

lease {
  interface "eth1";
  option subnet-mask;
  option routers;
  option dhcp-lease-time 3600;
  option dhcp-message-type 5;
  option domain-name-servers ...;
  option dhcp-server-identifier ...;
  option domain-name "...";
  renew 4 2021/02/04 13:10:16;
  rebind 4 2021/02/04 13:11:16;
  expire 4 2021/02/04 13:13:16;
The exchange with a DHCP server (that is down at the very moment) is nothing 
- Request
- Discover
- Discover
- Discover

(133 seconds passed) and stop. Of course the client starts using formerly 
assigned IP address of .

When the date changes at midnight so the 4th of February starts, the client 
starts sending DHCP Discovers again.
First couple questions are: Is this expected behaviour? If not so, why it 
stopped sending Discovers ? 

I was curious and manually modified the lease to expire not the next day but in 
30 minutes:

lease {
  interface "eth1";
  option subnet-mask;
  option dhcp-lease-time 3600;
  option routers;
  option dhcp-message-type 5;
  option dhcp-server-identifier ....;
  option domain-name-servers ....
  option domain-name "....";
  renew 3 2021/02/03 13:02:23;
  rebind 3 2021/02/03 13:03:23;
  expire 3 2021/02/03 13:05:23;
Interestingly the client did not start with DHCP Request as if the lease would 
already have expired. I thought it might have been the time-zone setting 
playing role but this was not the case checked the system UTC time and the 
lease should still be valid.
The client has kept sending Discovers perpetually and accordingly to the 
configured protocol timings (as one would expect) of course not getting any 
offer (server still down).

Would the afore described behaviour be an indication of an undocumented feature 
(bug) ? I read in the documentation that client stopping sending discovers 
after a timeout would be anticipated in the case of a valid static lease, which 
is not the case here.

I would hugely appreciate any insight in the described behaviour.
With my best wishes???? Tomasz Motyl
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