[Dnsmasq-discuss] ProxyDHCP replies on invalid range

[Alkis Georgopoulos]

Hi, I've filed this as a bug report in launchpad, but I'm forwarding it 
here as well upon request:
https://bugs.launchpad.net/ubuntu/+source/dnsmasq/+bug/1651044


In Ubuntu 16.04, I've configured dnsmasq to reply on 
subnet=10.160.37.0/24, yet it replies even when it gets an IP on 
subnet=10.161.254.0/24.

This happens after system restart, or after restarting dnsmasq with the 
ethernet cable unplugged.
If the ethernet cable is plugged in while restarting dnsmasq, it works 
as expected.
So maybe when dnsmasq starts and the network is down, it incorrectly 
initializes some networking information?
I'm using dnsmasq 2.75-1ubuntu0.16.04.1 on i386 architecture and 
network-manager 1.2.2-0ubuntu0.16.04.3 with DHCP.

Details:
$ egrep -rv '^#|^$' /etc/dnsmasq.*
/etc/dnsmasq.d/ltsp-server-dnsmasq.conf:dhcp-range=10.160.37.0,proxy
/etc/dnsmasq.d/ltsp-server-dnsmasq.conf:dhcp-range=192.168.67.20,192.168.67.250,8h
/etc/dnsmasq.d/ltsp-server-dnsmasq.conf:enable-tftp
/etc/dnsmasq.d/ltsp-server-dnsmasq.conf:tftp-root=/var/lib/tftpboot/
/etc/dnsmasq.d/ltsp-server-dnsmasq.conf:dhcp-option=17,/opt/ltsp/i386
/etc/dnsmasq.d/ltsp-server-dnsmasq.conf:dhcp-vendorclass=etherboot,Etherboot
/etc/dnsmasq.d/ltsp-server-dnsmasq.conf:dhcp-vendorclass=pxe,PXEClient
/etc/dnsmasq.d/ltsp-server-dnsmasq.conf:dhcp-vendorclass=ltsp,"Linux 
ipconfig"
/etc/dnsmasq.d/ltsp-server-dnsmasq.conf:dhcp-boot=net:pxe,/ltsp/i386/pxelinux.0
/etc/dnsmasq.d/ltsp-server-dnsmasq.conf:dhcp-boot=net:etherboot,/ltsp/i386/nbi.img
/etc/dnsmasq.d/ltsp-server-dnsmasq.conf:dhcp-boot=net:ltsp,/ltsp/i386/lts.conf
/etc/dnsmasq.d/ltsp-server-dnsmasq.conf:dhcp-option=vendor:pxe,6,2b
/etc/dnsmasq.d/ltsp-server-dnsmasq.conf:dhcp-no-override
/etc/dnsmasq.d/ltsp-server-dnsmasq.conf:pxe-service=X86PC, "Boot from 
network", /ltsp/i386/pxelinux

$ ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN 
group default qlen 1
     link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
     inet 127.0.0.1/8 scope host lo
        valid_lft forever preferred_lft forever
     inet6 ::1/128 scope host
        valid_lft forever preferred_lft forever
2: enp2s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast 
state UP group default qlen 1000
     link/ether d0:50:99:a6:bc:0a brd ff:ff:ff:ff:ff:ff
     inet 10.161.254.185/24 brd 10.161.254.255 scope global dynamic enp2s0
        valid_lft 431873sec preferred_lft 431873sec
     inet6 fe80::f363:c1e2:9cb8:d9e2/64 scope link
        valid_lft forever preferred_lft forever

$ sudo netstat -nap | grep dnsmasq
[sudo] password for administrator:
tcp 0 0 0.0.0.0:53 0.0.0.0:* LISTEN 843/dnsmasq
tcp6 0 0 :::53 :::* LISTEN 843/dnsmasq
udp 0 0 0.0.0.0:53 0.0.0.0:* 843/dnsmasq
udp 0 0 0.0.0.0:67 0.0.0.0:* 843/dnsmasq
udp 0 0 0.0.0.0:69 0.0.0.0:* 843/dnsmasq
udp 0 0 0.0.0.0:4011 0.0.0.0:* 843/dnsmasq
udp6 0 0 :::53 :::* 843/dnsmasq
udp6 0 0 :::69 :::* 843/dnsmasq
unix 2 [ ] DGRAM 15746 843/dnsmasq

$ grep dnsmasq /var/log/syslog | tail -n 30
Dec 19 10:52:17 ltsp-server systemd[1]: Starting dnsmasq - A lightweight 
DHCP and caching DNS server...
Dec 19 10:52:17 ltsp-server dnsmasq[630]: dnsmasq: syntax check OK.
Dec 19 10:52:20 ltsp-server dnsmasq[843]: started, version 2.75 
cachesize 150
Dec 19 10:52:20 ltsp-server dnsmasq[843]: compile time options: IPv6 
GNU-getopt DBus i18n IDN DHCP DHCPv6 no-Lua TFTP conntrack ipset auth 
DNSSEC loop-detect inotify
Dec 19 10:52:20 ltsp-server dnsmasq[843]: DNS service limited to local 
subnets
Dec 19 10:52:20 ltsp-server dnsmasq-dhcp[843]: DHCP, IP range 
192.168.67.20 -- 192.168.67.250, lease time 8h
Dec 19 10:52:20 ltsp-server dnsmasq-dhcp[843]: DHCP, proxy on subnet 
10.160.37.0
Dec 19 10:52:20 ltsp-server dnsmasq-tftp[843]: TFTP root is 
/var/lib/tftpboot/
Dec 19 10:52:20 ltsp-server dnsmasq[843]: no servers found in 
/var/run/dnsmasq/resolv.conf, will retry
Dec 19 10:52:20 ltsp-server dnsmasq[843]: read /etc/hosts - 7 addresses
Dec 19 10:52:23 ltsp-server systemd[1]: Started dnsmasq - A lightweight 
DHCP and caching DNS server.
Dec 19 10:52:29 ltsp-server dnsmasq[843]: reading 
/var/run/dnsmasq/resolv.conf
Dec 19 10:52:29 ltsp-server dnsmasq[843]: ignoring nameserver 127.0.0.1 
- local interface
Dec 19 10:52:29 ltsp-server dnsmasq[843]: using nameserver 194.63.238.4#53
Dec 19 10:52:29 ltsp-server dnsmasq[843]: using nameserver 8.8.8.8#53
Dec 19 08:52:47 ltsp-server dnsmasq-dhcp[843]: PXE(enp2s0) 
52:54:00:8f:74:ad proxy
Dec 19 08:52:47 ltsp-server dnsmasq-dhcp[843]: PXE(enp2s0) 
10.161.254.195 52:54:00:8f:74:ad /ltsp/i386/pxelinux.0
Dec 19 08:52:47 ltsp-server dnsmasq-tftp[843]: sent 
/var/lib/tftpboot/ltsp/i386/pxelinux.0 to 10.161.254.195
...

Note that it replies in "52:54:00:8f:74:ad proxy" while it shouldn't.
If I run this:
# service dnsmasq restart

Then it behaves correctly:
Dec 19 09:01:17 ltsp-server dnsmasq-dhcp[2381]: no address range 
available for DHCP request via enp2s0


Kind regards,
Alkis Georgopoulos