Jan 082007
 

Sponsored Link

A DNS server resolves domain names into IP addresses. So when you request “yahoo.com” for example, the DNS server finds out the address for the domain, and sends your request the right way.

You can run a DNS cache on your computer. This will speed up the process of looking up domain names when browsing. The difference is about 30-60 ms. Multiply that difference by the number of websites you visit a day for an approximate estimate of the speed improvement.

The following instructions are for someone with a broadband internet connection, where the computer gets it’s local IP address using DHCP from the router in your home or office.

Install dnsmasq in Ubuntu

Dnsmasq is a lightweight, easy to configure, DNS forwarder and DHCP server. It is designed to provide DNS and optionally, DHCP, to a small network. It can serve the names of local machines which are not in the global DNS. The DHCP server integrates with the DNS server and allows machines with DHCP-allocated addresses to appear in the DNS with names configured either in each host or in a central configuration file. Dnsmasq supports static and dynamic DHCP leases and BOOTP for network booting of diskless machines.

First you need to make sure that Universe repository is enabled in your sources.list file

Install dnsmasq Using the following command

sudo apt-get install dnsmasq

uncomment the following line (remove “#” in the beginning) in the file /etc/dnsmasq.conf

listen-address=127.0.0.1

Now edit

/etc/dhcp3/dhclient.conf

and make sure the section below exactly like this, especially the line that says “prepend domain-name-servers 127.0.0.1;”

#supersede domain-name “fugue.com home.vix.com”;
prepend domain-name-servers 127.0.0.1;
request subnet-mask, broadcast-address, time-offset, routers,
domain-name, domain-name-servers, host-name,
netbios-name-servers, netbios-scope;

In the normal case, when you get a new dhcp lease, the dhcp3 client (tool) on your computer gets a new lease, and updates the

/etc/resolv.conf

file on your computer with the right values for the DNS servers to use (usually some machine in the network of your hosting provider). Adding the “prepend” option as we did above ensures that “127.0.0.1″ will appear on the top of the list of DNS servers. That magic number refers to your own computer. So in the future, whenever your computer needs to resolve a domain name, it will forward that request to dnsmasq (which is running at 127.0.0.1 -- your computer). If the details for the domain name are already in you cache, well and good, dnsmasq will serve it up and make the process real fast. If it is not in the cache, then dnsmasq will look at the /etc/resolv.conf file and use the nameservers listed below the “127.0.0.1?. I hope that explains things.

Now open the file

/etc/resolv.conf

in your text editor. It probably looks like:

search yourisp.com
nameserver 217.54.170.023
nameserver 217.54.170.024
nameserver 217.54.170.026

The 127.0.0.1 is missing right now since you haven’t renewed your lease after you edited the /etc/dhcp3/dhclient.conf file. So, let us add that in manually this one time. After you do, your /etc/resolv.conf file will look like the following:

search yourisp.com
nameserver 127.0.0.1
nameserver 217.54.170.023
nameserver 217.54.170.024
nameserver 217.54.170.026

Now you need to restart the dnsmasq using the following command

sudo /etc/init.d/dnsmasq restart.

Now you are running a local DNS cache.

Testing Your Local DNS Cache

If you want to measure your speed improvement, type the command

dig yahoo.com

You will see something like “;; Query time: 38 msec” there.

Now type the command again, and you should see something like:”;; Query time: 2 msec”

Sponsored Link

 Posted by at 8:57 am
  • jba

    Question: Can other machines use this as a cache as well, just by pointing to my server (with dnsmasq) as a DNS server ?

  • B9

    Hey, jba!
    All machines on your LAN can use the dns server by pointing to it’s ip address. [B9]

  • helpdeskdan

    Good tutorial, but why use dnsmasq when you can use pdnsd? The cache doesn’t erase every time you reboot.

    http://ubuntuforums.org/showthread.php?t=331850

  • Tuishimi

    Another problem, when tunneling (PPTP) into a windows network, I no longer pick up the DNS servers from that network. And my resolv.conf is dynamically generated so I have no idea where to stick the DNS Server IP addresses, or how to get them recognized.

  • Luis

    Excellent post, thank you so much! One remark: On ubuntu 11.10, dhclient.conf is located under /etc/dhcp, not /etc/dhcp3