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Today's Topics:
1. Curious behaviour with expired/abandoned leases not being
given out (Christopher Causer)
----------------------------------------------------------------------
Message: 1
Date: Tue, 10 Mar 2020 13:48:29 +0000
From: Christopher Causer <christopher.cau...@it.ox.ac.uk>
To: "dhcp-users@lists.isc.org" <dhcp-users@lists.isc.org>
Subject: Curious behaviour with expired/abandoned leases not being
given out
Message-ID:
<cwlp265mb00993681e85fe3ccaa723f7d88...@cwlp265mb0099.gbrp265.prod.outlook.com>
Content-Type: text/plain; charset="us-ascii"
Hi DHCP Users list,
May I please have some help understanding what is going on here? I have a pool
that by some accounts is not full and in others it is and I don't understand
why.
The logs indicate that it is pushing close to the limits of free addresses when
balancing
2020-03-10T10:53:19+00:00 $PRIMARY dhcpd[2147]: balanced pool 55dccc4d51e0
10.20.200.0/22 total 1008 free 2 backup 2 lts 0 max-misbal 1
2020-03-10T10:53:20+00:00 $SECONDARY dhcpd[3683]: balanced pool 555eee5eb1e0
10.20.200.0/22 total 1008 free 2 backup 2 lts 0 max-misbal 1
And this is confirmed when some people try to get leases
2020-03-10T10:54:22+00:00 $PRIMARY dhcpd[3683]: DHCPDISCOVER from $MAC via
10.20.203.254: peer holds all free leases
2020-03-10T10:54:22+00:00 $SECONDARY dhcpd[2147]: DHCPDISCOVER from $MAC via
10.20.203.254: peer holds all free leases
However we run dhcpd-pools. The subnet is 43% utilized, but 100% "touch
utilized":
$ dhcpd-pools
Ranges:
shared net name first ip last ip max cur percent
touch t+c t+c perc bu bu perc
[snip]
All networks 10.20.200.1 - 10.20.203.240 1008 434 43.056
573 1007 99.901 1 0.099
What is happening here? I can see the touched percentage being high, but as I
understand it that should not be denying any leases being given out. According
to the dhcpd-pools man page, touched IPs are "
IP's which appear in the lease file, but who's leases have expired. A touched
IP is either expired or abandoned." We have many subnets and there are only two
with a touch percentage of ~100% and these are both subnets experiencing issues.
I've set the abandon-lease-time to 1800. Running ping against the subnet,
sources from the DHCP server, I do not get anywhere close to 50% responses.
Any help gratefully received. Redacted config below. The leases file is too
large and contains sensitive data that I don't think my employer would be
willing to hand out unfortunately. I am happy to redact and share relevant
snippets if required though.
# /etc/dhcp/dhcpd.confcd
-------------------------------------------------->8-------------
ddns-updates off;
ddns-update-style none;
authoritative;
log-facility local7;
local-address $IP;
server-identifier $IP;
key EXKEY {
[snip]
};
omapi-port 7911;
omapi-key EXKEY;
include "/etc/dhcp/options.conf";
include "/etc/dhcp/failover.conf";
include "/etc/dhcp/nets.conf";
-------------------------------------------------->8-------------
## /etc/dhcp/options.conf
-------------------------------------------------->8-------------
option option-150 code 150 = array of ip-address;
-------------------------------------------------->8-------------
## /etc/dhcp/failover.conf
-------------------------------------------------->8-------------
failover peer " dhcp" {
primary;
address $THIS_ADDRESS;
port 847;
peer address $PEER_ADDRESS;
peer port 848;
max-response-delay 5;
max-unacked-updates 10;
load balance max seconds 3;
# ONLY ON PRIMARY
mclt 1800;
split 128;
# /ONLY ON PRIMARY
}
-------------------------------------------------->8-------------
## /etc/dhcp/nets.conf
# Very long, so snipped considerably
-------------------------------------------------->8-------------
abandon-lease-time 1800;
default-lease-time 900;
max-lease-time 900;
ping-check false;
one-lease-per-client true;
boot-unknown-clients true;
option domain-name-servers [snip];
option domain-name "[snip]";
option time-servers uk.pool.ntp.org;
subnet 10.20.200.0 netmask 255.255.252.0 {
option routers 10.20.203.254;
option subnet-mask 255.255.252.0;
pool {
deny dynamic bootp clients;
failover peer "dhcp";
range 10.20.200.1 10.20.203.240;
}
}
-------------------------------------------------->8-------------
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