Posts Tagged ‘internet service provider’

Set ISP provider default DNS to overwrite DHCP settings on Debian / Ubuntu Linux

Monday, February 11th, 2013

dhcp linux ovewrite dns settings from console and terminal Debian Ubuntu Fedora CentOS Linux
 

These days, almost every home wireless ISP network router, ADSL modem etc. has its own local running DNS service. Generally this is very good as it puts off the burden of  Internet Service Provider DNS servers and "saves" multitude of users from so common overloads with ISP DNS Servers – caused by ISP DNS Service unable to handle the incoming user DNS (Domain resolve) traffic. Common scenario, where ISP DNS servers is unable to handle DNS traffic is when few thousands of users belonging to ISP gets infected with a Worm, Trojan horse or Virus doing plenty of DNS Spoofs and distributed DDoS attacks.

Though local DNS service (daemons) on local Cable and Wireless Network Routers is something designed to be good it becomes another bottleneck for DNS resolve problems, Calling the ISP tech support for help is often loose of time, as  in ISPs it is so rare to find someone understanding Linux Networking.

The periodic issues with DNS resolving from home routers in my observations has 3 main reasons;

  • Local Cheap network Wireless routers with slow hardware (CPU) and little memory are unable to handle DNS requests, because of torrent Downloads
     
  • DNS Wireless Router can't handle DNS requests to its DNS local service, because a small local network of computers with a landline and wireless (lets say 5 to 10) is trying to access the Internet (browsing) – again due to its low hardware paremeters router CPU heats up cause of multitude of DNS requests

     

  • Something is wrong with general network topology of PCs behind the router. Often people buy a router and use it shared with their neighbors – tampering with Router settings messing it up.

DNS resolving problems are even harder to track whether Internet provider has policy to deliver Internet via automated IP assignment protocol (DHCP),

A very common scenario, I've seen is Internet coming via ISP ADSL / Network router installed at home and mis-configured due to a custom user installation,   or because of ISP technician who installed router in hurry or lacked good competency and messed up with Router Network configuration.

During the years I had to install various Linux distributions for Desktop use in networks located behind such mis-configured Network Hubs. Because of this mis-configured DNS, even though Linux hosts succesfully graps the IP addresses for host IP, Gateway and DNS, they occasionally create problems with Internet Connection leaving the user with impression that Linux is not ready for Desktop use or somehow it is the the Linux distro fault.

After giving an introduction I will continue further to exact problem I've faced with one such mis-configured just today. The same issue has happened in my sysadmin practice over and over again so many times. So finally I decided to write this small story explaining the whole scenario, its causes and fix.

I'm writing this little post from another Linux installation like this which is living on a small local network served by a Vivacom ISP through ADSL Commtrend SmartAX MT882 Router.

The Commtrend does NAT (Network Address Translation)-ting for whole local network, auto-assigning some DNS server to Natted IP PCs local Network addresses in IP raneg; (172.16.0.0-255). The DNS the router assigns for internet is with IP (172.16.0.1), where in reality the DNS on the router is run on Network interface with IP 1921.68.1.1, in other words belonging to the router from another network. Thus PCs connected via a UTP land-line cable connection does not see 192.168.1.1 – meaning Domain name resolving works not at all.
The solution is to assign a static IP address for DNS of Google Public DNS or Open DNS, while leaving the Linux host to automatically assign LAN IP and Gateway using DHCP – (Dynamic Host Configuration Protocol).

By default most Linux distributions use DNS configured in /etc/resolv.conf as a host DNS servers, however as CommTrend Network Router does provide settings for DNS Servers to be used for resolving along with other settings on each Linux host boot settings from /etc/resolv.conf gets ovewritted with the unreachable (from 172.16.0.255), nameserver 192.168.1.1.

Thus to work-around this on most all Linux distributions you can set /etc/resolv.conf to be overwritten adding a line to /etc/rc.local script (before its last line – exit 0);

echo 'nameserver 8.8.8.8' > /etc/resolv.conf
echo 'nameserver 8.8.4.4' >> /etc/resolv.conf

This method is universal, but the problem with it arises, if on the Linux host is planned to run 24 hours a day. DHCP Servers on router has configured DHCP Expiry lease time, which is different on different routers but usually few hours i.e. (4 hrs). Thus in 4 hours, due to DHCP Lease expiry the Linux host will question the DHCP Server for IP, getting together with DHCP IP and Gateway Settings also a DNS IP (overwritting again /etc/resolv.conf – with local running ISP Router IP – 192.168.1.1). One stupid solution of course is to use good old Windows philosophy (reboot it and it will work).

Other little more intelligent but not very efficient solution to problem is to set a cronjob, to run every 1 minute and overwrite /etc/resolv.conf DNS setting.

# crontab -u root -e

*/1 * * * * echo -e 'nameserver 8.8.8.8\nnameserver 8.8.4.4' > /etc/resolv.conf >/dev/null 2>&1

Since the cronjob to overwrite DNS IPs runs every one minute it is possible the host ends up without internet from few secs to 1 minute, this might happen quite rare so for a desktop this is ok. Other inconvenience is it puts a tiny load on system every 1 minute.

Final and best solution is to configure DNS server from /etc/dhcp/dhclient.conf  for Ethernet Interface eth0. Inside /etc/dhcp/dhclient.conf for eth0 make sure you have:

# vi /etc/dhcp/dhclient.conf

interface "eth0" {
prepend domain-name-servers 8.8.8.8;
prepend domain-name-servers 8.8.4.4;
prepend domain-name-servers 208.67.222.222;
prepend domain-name-servers 208.67.220.220;
}

Speed up your DNS resolve if your Internet Service Provider DNS servers fail or resolve slowly / Privacy concerns of public DNS services use

Wednesday, March 30th, 2011

In my experience with many network Internet Service Providers by so far I’ve encountered a lot of DNS oddities and therefore surfing (web) and mail slowness.

It’s sometimes very irritating especially in cases, when I use my internet over Wireless public or university wireless networks.
In principle many of the Wireless routers which distribute the internet especially in organizations are badly configured and the slowness with DNS resolvings is an absolute classic.
If you haven’t encountered that slowness in opening web pages when connected from your University’s canteen, whether it’s fill with people for the lunch break, then I should say you’re really lucky!

My personal experience with this bad configured devices DNS services has been quite negative and every now and then I use to set and use public DNS servers like OpenDNS and Google DNS

Very often when I connect to a wireless network with my notebook running Debian Linux and the internet is too slow in opening pages I automatically set the Google or OpenDNS servers as a default DNS IP resolving servers.

1. DNS IP addresses of Google Public DNS are:

8.8.8.7
and
8.8.8.8

2. OpenDNS Public DNS servers has the IP addresses of:

208.67.222.222
208.67.222.220

I do set up and use the upper public DNS services addresses via the commands:

3. Set and use Google Public DNS services on my Linuxdebian:~# cp -rpf /etc/resolv.conf /etc/resolv.conf.orig
debian:~# echo "nameserver 8.8.8.7n nameserver 8.8.8.8 n" > /etc/resolv.conf;

I first create backu pof my resolv.conf under the name resolv.conf.orig just to make sure I can revert back to my old DNSes if I need them at some point.

If you prefer to use the OpenDNS services for some let’s say privacy reasons, you do it in the same manner as in the above commands, you only change the IP addresses. 4. Configure and use the OpenDNS public DNS services

debian:~# cp -rpf /etc/resolv.conf /etc/resolv.conf.orig
debian:~# echo "nameserver 208.67.222.222n nameserver 208.67.222.220 n" > /etc/resolv.conf;

Of course using Public DNS services has it’s disadvantages over the domain resolving speed up advantage.
One major issue is that Public DNS services are running on a top of a cloud and if you have red my previous article Cloud Computing a possible threat to users privacy and system administrator employment you might be agaist the idea of using a services which are powered by cloud.

The other primary concern is related to your SECURITY and a PRIVACY by using Public DNS networks, you risk that your Public DNS provider might use some DNS spoof techniques to mislead you and resolve you common domain names which usually resolve to let’s say 1.1.1.1 to let’s say 1.5.5.10

Even though this kind of practices on a side of a public DNS provider is not a likely scenario the possible implications of Public DNS providers using DNS forgery to fool you about domain names locations is a very serious issue.

As public DNS providers does contain again the good old philosophy of cloud computing embedded in themselves and they strive to become some kind of a standard which people might vote to adopt and use, the future implications of a wide adoption of Public DNS servers might be a terrible thing on internet users privacy!!!

Just think about a future scenario where we users of the Internet are forced to use a number of public DNS servers in order to use the Internet!
Usually a very huge companies are possessing the Public DNS services and do pay for the tech equipment required for building up the cluster clouds which provide the DNS services and therefore, if in the short future public DNS becomes a fashion and (God forbid!) a standard which shifts up the regular ISP DNS servers to resolve domains to IPs then it will be terrible.

The corporations which does own the Public DNS service/s might have a direct control over filtering and censoling information posted on any website on the internet.
Even worser if the world decides to adopt public DNS services somewhere in the future this means that large corporations owning the open dns cluster or clusters will be able to check each and every resolving made by any user on the net.
If you think closely such an information possessed by a company is not the best thing we want.

So let me close up this article, I’m not a fan and an evangelist who preaches the use of Public DNS services. Right on Contrary I do honestly hate the idea behind public DNS.
Nevertheless apart from my personal opinion I’m a practical person and using the public DNS servers every now and then when this will accelerate my access to the internet is still an option I do enjoy.

Maybe it’s time for a free software project (a tor like), which will provide users with an OpenDNS alternative which will run on hobbyist computers around the globe (just like with tor).

What’s rather funny is that the loud name OpenDNS is a big lie in reality OpenDNS is not opened it’s a company owned closed source service 😉