[Dnsmasq-discuss] DHCP offers are not accepted

Marc Elbirt elbirt at gmail.com
Mon Dec 31 20:44:32 GMT 2018


## Expected Behaviour:
DHCP offers should be accepted by any client

## Actual Behaviour:
Clients repeatedly ask for DHCP addresses, every 3 seconds, overwhelming
pi-hole and slowing all responses (including DNS). Some client devices
(iPhone 7) can be observed to temporarily acquire an address, and then drop
it moments later.

## Debug Token:
eepv3gugqb

## Versions:
Dnsmasq version 2.76  Copyright (c) 2000-2016 Simon Kelley
FTL Version v4.1.2
Linux pi-hole 4.14.79+ #1159 Sun Nov 4 17:28:08 GMT 2018 armv6l GNU/Linux
Raspbian GNU/Linux 9 (stretch)

## Config notes:
pi-hole is configured for DNS and DHCP, on subnet 192.168.2.1/24. It is
configured to grant infinite leases to any, in the range 192.168.2.129 to
192.168.2.223, and most devices (including the ones below) have been
allocated static leases in the space below this range.

## Example:
Dec 28 08:35:18 dnsmasq-dhcp[882]: DHCPDISCOVER(wlan0) 44:61:32:xx:xx:xx
Dec 28 08:35:18 dnsmasq-dhcp[882]: DHCPOFFER(wlan0) 192.168.2.26
44:61:32:xx:xx:xx
Dec 28 08:35:18 dnsmasq-dhcp[882]: DHCPREQUEST(wlan0) 192.168.2.26
44:61:32:xx:xx:xx
Dec 28 08:35:18 dnsmasq-dhcp[882]: DHCPACK(wlan0) 192.168.2.26
44:61:32:xx:xx:xx ecobee3
Dec 28 08:35:21 dnsmasq-dhcp[882]: DHCPREQUEST(wlan0) 192.168.2.26
44:61:32:xx:xx:xx
Dec 28 08:35:21 dnsmasq-dhcp[882]: DHCPACK(wlan0) 192.168.2.26
44:61:32:xx:xx:xx ecobee3
...
Dec 28 08:36:23 dnsmasq-dhcp[882]: DHCPREQUEST(wlan0) 192.168.2.58
68:c6:3a:xx:xx:xx
Dec 28 08:36:23 dnsmasq-dhcp[882]: DHCPACK(wlan0) 192.168.2.58
68:c6:3a:xx:xx:xx PurpleAir_751
Dec 28 08:36:26 dnsmasq-dhcp[882]: DHCPREQUEST(wlan0) 192.168.2.58
68:c6:3a:xx:xx:xx
Dec 28 08:36:26 dnsmasq-dhcp[882]: DHCPACK(wlan0) 192.168.2.58
68:c6:3a:xx:xx:xx PurpleAir_751
Dec 28 08:36:28 dnsmasq-dhcp[882]: DHCPREQUEST(wlan0) 192.168.2.58
68:c6:3a:xx:xx:xx
Dec 28 08:36:28 dnsmasq-dhcp[882]: DHCPACK(wlan0) 192.168.2.58
68:c6:3a:xx:xx:xx PurpleAir_751

## Notes:
Testing with nmap reveals unexpected behavior, where lease time is set to
the minimum dnsmasq time (2 mins):
Starting Nmap 7.70 ( https://nmap.org ) at 2018-12-28 08:12 PST
Pre-scan script results:
| broadcast-dhcp-discover:
|   Response 1 of 1:
|     IP Offered: 192.168.2.148
|     DHCP Message Type: DHCPOFFER
|     Server Identifier: 192.168.2.10
|     IP Address Lease Time: 2m00s
|     Renewal Time Value: 1m00s
|     Rebinding Time Value: 1m45s
|     Subnet Mask: 255.255.255.0
|     Broadcast Address: 192.168.2.255
|     Domain Name Server: 192.168.2.10
|     Domain Name: xxxxxxxx
|_    Router: 192.168.2.1
WARNING: No targets were specified, so 0 hosts scanned.
Nmap done: 0 IP addresses (0 hosts up) scanned in 4.23 seconds
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