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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 <butterfly_tm...@yahoo.com>
To: "dhcp-users@lists.isc.org" <dhcp-users@lists.isc.org>
Subject: Inconsistent behaviour with a valid lease(s) in the leases'
DB and no DHCP server up.
Message-ID: <958082568.1709133.1613460345...@mail.yahoo.com>
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";
fixed-address 10.1.1.92;
option subnet-mask 255.255.255.128;
option routers 10.1.1.1;
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
extraordinary:
- Request
- Discover
- Discover
....
- Discover
(133 seconds passed) and stop. Of course the client starts using formerly
assigned IP address of 10.1.1.92 .
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";
fixed-address 10.1.1.92;
option subnet-mask 255.255.255.128;
option dhcp-lease-time 3600;
option routers 10.1.1.1;
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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