Dnsmasq for Home User

Updated: Aug 05, 2012

Every BSNL broadband subscribers know that BSNL’s default nameservers are one of the worst in response times. Even if you have connectivity exceeding 1gbps, If your nameservers are not good, then your internet experience will not be good.

So, I decided to use google’s nameservers. I could have configure NetworkManager not to get nameservers through DHCP instead ask it to use google’s nameservers, but I thought of giving dnamasq a try.

../../_images/dnsmasq_icon.jpg

For those who don’t know what is mean by dnsmasq, it is a dns forwarder which can handle DNS, DHCP and BOOTP requests. It means, it can act like bind, dhcpcd and tftpd.

Configuring dnsmasq is pretty simple and straight forward. We have to modify two files /etc/hosts and /etc/dnsmasq.conf. Here is my /etc/hosts file

127.0.0.1     mokka.drunkenmonk.org mokka localhost
::1           mokka.drunkenmonk.org mokka localhost
192.168.2.1   bridge.mokka.drunkenmonk.org

The first line says 127.0.0.1 is the ip address for mokka.drunkenmonk.org and also for mokka and localhost hostnames. I other words, mokka, localhost and mokka.drunkenmonk.org will resolve to 127.0.0.1 ip address.

mokka.drunkenmonk.org is a cononical name which contains two parts, mokka as hostname and drunkenmonk.org as domainname. So, by putting drunkenmonk.org, I’m also setting domainname for my system.

I really don’t know the proper way to configure domainname in my sabayon (in other words gentoo). From googling, I came to know that putting domain drunkenmonk.org into /etc/resolv.conf is the right way to set domainname in a linux system. But, /etc/resolv.conf is such dynamic nowadays, we can’t be sure who will modify it later and I never see a router providing domainname in DHCP response (Not in BSNL’s ADSL routers for sure). So I endup putting my domainname in /etc/hosts file.

The second line is same like the first one, but for ipv6.

The third line says 192.168.2.1 is the ip address for bridge.mokka.drunkenmonk.org. I’ll come to this later. Now, take a look at my /etc/dnsmasq.conf

domain-needed
bogus-priv
no-resolv
server=8.8.8.8
server=8.8.4.4
local=/drunkenmonk.org/
domain=drunkenmonk.org
dhcp-range=interface:br0,192.168.2.2,192.168.2.254,255.255.255.0,1d
mx-host=drunkenmonk.org,mail.drunkenmonk.org,30
cname=drunkenmonk.org,bridge.mokka.drunkenmonk.org
cname=www.drunkenmonk.org,bridge.mokka.drunkenmonk.org
cname=mail.drunkenmonk.org,bridge.mokka.drunkenmonk.org

domain-needed instructs dnsmasq to never forward DNS queries which don’t have domain part. It means, If you query for nslookup google dnsmasq will never forward it to upstream server (In my case, to google’s nameservers).

bogus-priv tells dnsmasq never forward reverse-lookup queries which have local subnet’s ip rage to upstream. Which means nslookup 10.0.0.1 will not be forwarded to upstream instead dnsmasq will try to resolv itself. If it doesn’t find hostname for 10.0.0.1 in /etc/hosts or its dhcp leases, then it will send back no such domain response.

no-resolv says dnsmasq will not read /etc/resolv.conf to get upsteram nameservers. Normally dnsmasq will read /etc/resolv.conf file to get upstream nameservers.

server=8.8.8.8 and server=8.8.4.4 instucts dnsmasq to use google’s 8.8.8.8 and 8.8.4.4 as primary and secondary DNS nameservers (or in other words upstream nameservers).

local=/drunkenmonk.org/ says that DNS queries with hostnames like mokka.drunkenmonk.org should not be forwarded to upstream intead dnsmasq should resolve it from /etc/hosts or from its dhcp leases.

domain=drunkenmonk.org tells dnsmasq to send domain=drunkenmonk.org in DHCP response so that machines configured through DHCP will come under drunkenmonk.org domain.

dhcp-range=interface:br0,192.168.2.2,192.168.2.254,255.255.255.0,1d instructs dhsmasq to allocate ip address between 192.168.2.2 and 192.168.2.254 with netmask 255.255.255.0 for 1 day only to the DHCP requests coming from br0 interface. Which means, machines connected through br0 interface and asking for DHCP response will get ip address between 192.168.2.2 and 192.168.2.254 for 1 day. dnsmasq will not send response to requests coming from interfaces other than br0.

mx-host=drunkenmonk.org,mail.drunkenmonk.org,30 tells dnsmasq to send mail.drunkenmonk.org as MX response for drunkenmonk.org domain. Which means, when you do nslookup -q=MX drunkenmonk.org it will give mail.drunkenmonk.org as response.

cname lines are like aliases. means when you do nslookup www.drunkenmonk.org it will resolve to bridge.mokka.drunkenmonk.org which resolves to 192.168.2.1 according to /etc/hosts file. So dnsmasq will send 192.168.2.1 as response.

Thats all from configuration stuff. These changes will take effect once you restart dnsmasq service. But this does not means that all your DNS queries will go through your machine’s dnsmasq daemon, If you have nameserver entry in /etc/resolv.conf, your machine’s DNS queries will go to /etc/resolv.conf nameservers. So, there is no use of using dnsmasq. You have to make sure you are not creating entries in /etc/resolv.conf. If you are a home user, make sure you select Automatic (DHCP) Address only in Method drop-down list inside ipv4 settings tab in NetworkManger.

You can check that you are getting response from dhsmasq with below commands,

$ dig ANY drunkenmonk.org
; <> DiG 9.9.1-P2 <> ANY drunkenmonk.org
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 39480
;; flags: qr aa rd ra ad; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;drunkenmonk.org.               IN      ANY
;; ANSWER SECTION:
drunkenmonk.org.        0       IN      CNAME   bridge.mokka.drunkenmonk.org.
bridge.mokka.drunkenmonk.org. 0 IN A    192.168.2.1
;; Query time: 0 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Mon Aug  6 00:15:16 2012
;; MSG SIZE  rcvd: 99

The line contains SERVER: tell us that our DNS query is served by 127.0.0.1, means our local machine. Here is the command to verify MX record,

$ dig MX drunkenmonk.org
; <> DiG 9.9.1-P2 <> MX drunkenmonk.org
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 14301
;; flags: qr aa rd ra ad; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;drunkenmonk.org.               IN      MX
;; ANSWER SECTION:
drunkenmonk.org.        0       IN      MX      30 mail.drunkenmonk.org.
;; Query time: 0 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Mon Aug  6 00:16:38 2012
;; MSG SIZE  rcvd: 71

If you are not introduced to Linux’s bridge interface, you may wonder what the hell is br0. Well , it is a virtual device in Linux which act like a physical network device (like eth0). I have particularly configured my dnsmasq to serve DHCP requests to whoever connect through my bridge interface. Howto use this br0 effectively to configure networking in my Qemu virtual machines is going to be my next Virtual Home Network (with Dnsmasq , Bridge, TUN/TAP, Qemu) article. Have a nice day!!