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Thread: How-To Stabilise your DNS addresses

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    Join Date
    Nov 2005

    How-To Stabilise your DNS addresses

    So if your problem is that your ISP's DNS addresses keep being lost after a reboot (sometimes it takes more than one reboot, sometimes it happens without a reboot!!)

    A possible symptom of this problem is not being able to use Synaptic Package Manager.

    What follows may solve your problem.

    Also, in this howto is a quick IPv6 fix for Firefox users, followed by a simple method that enables globally disabling IPv6 (added 22-Oct-07), which some may find they need to do to speed up their internet experience. There is also basic instructions for using keyboard combinations for cutting, pasting & moving text in & out of the Terminal & elsewhere, intended for those unfamiliar with the Terminal.

    All sections are easy to find when scrolling.

    If you are new to the Terminal, scroll down the page to the Text & the Terminal section.

    I have tested the following on Ubuntu's Dapper, Edgy, Feisty & Gusty, but not on the previous Breezy version of Ubuntu?

    For Breezy see Post 2. of this thread for Python's wonderful solution, it does not work in Dapper & beyond, unfortunately.

    The Case of the Disappearing DNS's

    After a great deal of trying work-arounds, even being driven to invent one myself, someone called Mips, finally pointed me to the solution.

    The following solution, pertaining to the dissapearing DNS's, is courtesy of Stream303 I've just made it easier for new users to follow.


    This is the way to prepend the resolv.conf file with your known good ISP's Domain Name Servers (DNS).

    Editing the /etc/dhcp3/dhclient.conf

    (If you are unfamiliar with using the Terminal have a look down this page for the Text & the Terminal section.)

    Enter the following line in the Terminal:

    sudo gedit /etc/dhcp3/dhclient.conf

    and just before the request line in your dhclient.conf file that you are looking at in gedit, add the following line, or remove the comment # from the start of the line if it is allready exists):

    prepend domain-name-servers,;

    You will probably want to swap your ISP's DNS addresses for the ones in the above example.

    ( You may also choose to leave them, as they are the legitimate OpenDNS IP's, & will work IF you edit your router's firmware via your browser & replace your ISP's DNS addresses with the OpenDNS ones. There are very simple & straight forward instructions for this on the OpenDNS website. If you don't know your ISP's DNS addresses, the OpenDNS how-to will show you how to get it from 95% of routers. If you still can't access your router you will have to google for the information.

    You can also allways check your ISP's web site or phone them if you don't have access to the addresses in documentation that your ISP supplied.

    I have been using OpenDNS for some time & am very pleased with the faster browsing speed, highly recommended.

    For multiple addresses, separate with a comma and don't forget the semicolon at the end.

    This will have the effect of prepending your ISP's nameservers and of having your routers DNS address automaticaly come up at the bottom of the list in resolv.conf.

    Reboot or just bring your interface down and up again by entering the following in the Terminal:

    sudo /etc/init.d/networking restart



    IPv6 Quick (Firefox) Fix

    If you can't access the web through Firefox, though you know you have an internet connection via your modem/router, OR you find it very slow to move between servers, after which browsing that server is as fast as it should be? Try the following:

    Enter about:config in Firefox's address field.

    Enter ipv6 in the new Filter: field.

    Double click on the line left in the display window to change it's boolean value to true.

    Restart Firefox.

    & that should be that...


    Disable IPv6 Globally

    Unlike the method of editing /etc/modprobe.d/aliases, the following method does not run the risk of being overwritten.

    Do the following to disable IPv6 globally:

    1. To verify that the IPv6 module is loaded type the following from a terminal:

    handy@birdfish:~$ lsmod | grep ipv6
    ipv6 265856 10

    2. Then from a terminal type:

    handy@birdfish:~$ sudo echo "blacklist ipv6" > /etc/modprobe.d/blacklist-ipv6

    3. Restart

    4. To verify that the IPv6 module is not loaded type the following from a terminal:

    handy@birdfish:~$ lsmod | grep ipv6

    If for whatever reason the above method does not work, type either of the following alternatives a. or b. in the terminal:

    a. echo "blacklist ipv6" | sudo tee -a /etc/modprobe.d/blacklist

    b. sudo nano -w /etc/modprobe.d/blacklist & enter the line blacklist-ipv6

    after both a. or b. do steps 3. & 4. as above.


    The reason for the first (DNS) problem which strikes lots of modem/routers is due to their windows centric design.

    The reason for the second (IPv6) problem is due to the cheap quality of the router, which is also responsible for the first problem...

    [Edit:] After having used other Linux distro's & PC-BSD, I have had to modify my conclusions as I have only experienced the above three problems when using *buntu, last verified on both (k)ubuntu 7.10.


    Text & the Terminal

    I know how it feels, having come from the windoze point & click for allmost everything environment, how intimidating it can feel, having to type arcane commands into the Terminal!

    We can get used to the Terminal surprisingly quickly.

    So often when we have found the help in the forums, wiki or other online reference we can just highlight with the mouse a command string & copy it into the Terminal on our own machine hit enter & move on... This method avoids typo's too!

    Very often, using commands in the Terminal is quicker by far than using a mouse.

    What follows are the few basic keyboard commands that make it all so easy.

    These keyboard shortcuts are not only useful for the
    Terminal they can be used for any other field that accepts text, the use of these keyboard shortcuts is only limited by your imagination. I use them all the time when writing in the forums. (All the 2 fingered ones are valid in windoze & DOS too!)

    If you highlight text by left mouse button dragging over the desired text you can use keyboard combo's to manipulate it.

    The most used 2 finger Key Combo's follow:

    Copy = < ctrl > + < c >

    Paste = < ctrl > + < v >

    Cut = < ctrl > + < x > Followed by the Paste combo' is Move.

    When manipulating text with Key Combo's, in the Terminal, (which is extremely useful) you are required to use the same combinations as above, with the addition of the < shift > key, making Terminal combo's 3 fingered.

    The Terminal is your friend...

    You will find both the Terminal & Text Editor in the Menu: Applications / Accessories

    The Text Editor (gedit is it's name if you call it from the Terminal) is both simple & powerful.

    For anyone wanting an online reference to the Terminal & beyond the 2 following links should keep you going for a long time:
    Last edited by handy; December 4th, 2009 at 03:32 AM. Reason: Added disabling IPv6 Globally


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