I have a network of Windows 10 machines served (DNS and DHCP) by a dnsmasq instance on a Ubuntu server (Ubuntu 15.10, dnsmasq 2.75). The setup basically works (dnsmasq provides addresses and manages DNS requests correctly) except for one specific case.
I wanted to provide a specific DNS server to one particular machine. I used the tag option in dnsmasq:
# open zone
dhcp-host=84:3a:4b:20:94:f0,set:open
# DNS for everyone = OpenDNS
dhcp-option-force=option:dns-server,208.67.222.222,208.67.220.220
# DNS for open = Google
dhcp-option-force=tag:open,option:dns-server,8.8.8.8,8.8.4.4
Upon ipconfig /renew on the client, the correct options are sent by dnsmasq:
root@srv ~# dnsmasq -d
dnsmasq: started, version 2.75 cachesize 150
dnsmasq: compile time options: IPv6 GNU-getopt DBus i18n IDN DHCP DHCPv6 no-Lua TFTP conntrack ipset auth DNSSEC loop-detect inotify
dnsmasq: reading /etc/resolv.conf
dnsmasq: using nameserver 192.168.0.254#53
dnsmasq-dhcp: DHCP, IP range 10.10.10.20 -- 10.10.10.100, lease time 5d
dnsmasq: cleared cache
dnsmasq-dhcp: 342453732 available DHCP range: 10.10.10.20 -- 10.10.10.100
dnsmasq-dhcp: 342453732 vendor class: MSFT 5.0
dnsmasq-dhcp: 342453732 client provides name: helloworld.example.com
dnsmasq-dhcp: 342453732 DHCPREQUEST(lan0) 10.10.10.21 84:3a:4b:20:94:f0
dnsmasq-dhcp: 342453732 tags: open, known, lan0
dnsmasq-dhcp: Ignoring domain example.com for DHCP host name helloworld
dnsmasq-dhcp: 342453732 DHCPACK(lan0) 10.10.10.21 84:3a:4b:20:94:f0 helloworld
dnsmasq-dhcp: 342453732 requested options: 1:netmask, 3:router, 6:dns-server, 15:domain-name,
dnsmasq-dhcp: 342453732 requested options: 31:router-discovery, 33:static-route, 43:vendor-encap,
dnsmasq-dhcp: 342453732 requested options: 44:netbios-ns, 46:netbios-nodetype, 47:netbios-scope,
dnsmasq-dhcp: 342453732 requested options: 121:classless-static-route, 249, 252
dnsmasq-dhcp: 342453732 next server: 10.10.10.254
dnsmasq-dhcp: 342453732 sent size: 1 option: 53 message-type 5
dnsmasq-dhcp: 342453732 sent size: 4 option: 54 server-identifier 10.10.10.254
dnsmasq-dhcp: 342453732 sent size: 4 option: 51 lease-time 5d
dnsmasq-dhcp: 342453732 sent size: 4 option: 58 T1 2d8h23m1s
dnsmasq-dhcp: 342453732 sent size: 4 option: 59 T2 4d5h23m1s
dnsmasq-dhcp: 342453732 sent size: 4 option: 1 netmask 255.255.255.0
dnsmasq-dhcp: 342453732 sent size: 4 option: 28 broadcast 10.10.10.255
dnsmasq-dhcp: 342453732 sent size: 4 option: 3 router 10.10.10.254
dnsmasq-dhcp: 342453732 sent size: 4 option: 15 domain-name testlab
dnsmasq-dhcp: 342453732 sent size: 18 option: 81 FQDN 03:ff:ff:6c:77:35:79:6f:70:32:64:73:79:2e...
dnsmasq-dhcp: 342453732 sent size: 8 option: 6 dns-server 8.8.8.8, 8.8.4.4
dnsmasq-dhcp: 342453732 sent size: 1 option: 46 netbios-nodetype 08
dnsmasq-dhcp: 342453732 sent size: 4 option: 44 netbios-ns 10.10.10.254
So the client is given the IP 10.10.10.21 (I changed it during the tests and the correct one is assigned every time, for every change - so the response to the request is correctly interpreted by the client) and, among others, the specific DNS servers.
Everything looks good from the dnsmasqside.
On the client I get
Wireless LAN adapter Wi-Fi:
Connection-specific DNS Suffix . : testlab
Description . . . . . . . . . . . : Intel(R) Centrino(R) Advanced-N 6205
Physical Address. . . . . . . . . : 84-3A-4B-20-94-F0
DHCP Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes
Link-local IPv6 Address . . . . . : fe80::74d6:d6c:a5cc:54c7%8(Preferred)
IPv4 Address. . . . . . . . . . . : 10.10.10.21(Preferred)
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Lease Obtained. . . . . . . . . . : samedi 2 avril 2016 15:59:55
Lease Expires . . . . . . . . . . : jeudi 7 avril 2016 16:03:15
Default Gateway . . . . . . . . . : 10.10.10.254
DHCP Server . . . . . . . . . . . : 10.10.10.254
DHCPv6 IAID . . . . . . . . . . . : 75774539
DHCPv6 Client DUID. . . . . . . . : 00-01-00-01-1C-87-7B-B4-3C-97-0E-67-52-6C
DNS Servers . . . . . . . . . . . : 10.10.10.254
Primary WINS Server . . . . . . . : 10.10.10.254
NetBIOS over Tcpip. . . . . . . . : Enabled
I checked with Wireshark on the client the received traffic. In the DHCP ACK packet (the one recived from the DHCP server) the option is correct (so it was no stripped on the way or something like this):
The IP is OK but the DNS server is not correct: it defaults to the DHCP server - it looks like the received option is not correctly interpreted (?)
