some questions about DNS problems

[ITlover]

I have some questions about DNS problems. For example if i am not able to connect to a perticular website and i can access other websites, then does it mean that there is something wrong with that website or webserver only and there is nothing wrong with the ISP and my DNS cache?

My other question is that if for example i have fully qualified domain names- IP addresses saved in my DNS cache and something goes wrong with the DNS of the ISP Server, then will i be able to connect to the websites for which i have name to IP resolution in my cache?


I hope my questions are clear

Prompt response would be appreciated.

[Petef56]

Originally Posted by ITlover I have some questions about DNS problems. For example if i am not able to connect to a perticular website and i can access other websites, then does it mean that there is something wrong with that website or webserver only and there is nothing wrong with the ISP and my DNS cache?

One way to find out if it's realted to your PC is to go to the command prompt
and issue the following command.. ipconfig /flushdns

If that reloves your problem then it was your PC's DNS cache.

---pete---

[Kareeser]

I have some questions about DNS problems. For example if i am not able to connect to a perticular website and i can access other websites, then does it mean that there is something wrong with that website or webserver only and there is nothing wrong with the ISP and my DNS cache?

It is rare for a DNS to become corrupted or stale, and they routinely drop their records for refreshing.

My other question is that if for example i have fully qualified domain names- IP addresses saved in my DNS cache and something goes wrong with the DNS of the ISP Server, then will i be able to connect to the websites for which i have name to IP resolution in my cache?

If your router has been to that site before, and knows to associate that particular IP address with that particular domain, then yes, it will work.

[perkster]

you can also use openDNS servers if you think it may be your ISPs DNS servers.

flushing your DNS cache will fix any issues with sites you fix often but suddenly stop working, maybe they changed their address slightly.

but usually when its just one site that wont load it is their website

[ITlover]

what is the job of router apart from connecting the two different subnets?

does it also direct the request of the client machines to the appropriate destination?

For example if i want to access a yahoo website, then the router will send the request to the port 80 since the http servers have a port 80?

[perkster]

thats done more by your TCP/IP settings i believe, but the router will often give out IP addresses for computers on the network and manage their data sends and requests and it can also sometimes obtain the DNS server info from the ISP saving you entering these

[ITlover]

Thanks for your replies. So all the users using the dial up service for internet by connecting to the same ISP will be counted in Local Area Network and the other users accessing the internet from other ISP service will be counted in external network(for users like me). pls correct me if i am wrong.

Does Router also resolves domain names into IP addresses?
As far as i know, it manages the flow of data traffic and also allows communication between DHCP Servers and DHCP Clients?

[perkster]

some routers have their own DNS cache which may be used if you visit a site often but generally no, the resolving of IP addresses from domain names is done by DNS servers which in most cases belong to your ISP, unless you use openDNS.com

[ITlover]

what is openDNS.com?

I just visited a thread in this forum , and someone said that if we type a perticular IP address in the address bar of the browser window and press enter and if we get a google site, then it means that something is wrong with DNS Server?


can anyone pls quote that ip address here for me?

How come by geting a google in reply, we can know that it is a DNS Server problem?

Thank you for your info about routers, so it means that if we clear our computers DNS cache and still after that we are not able to access websites, then there could be a problem with the DNS cache of the router, not necessarily the DNS of the ISP Server?

Is there a way we could clear the routers DNS cache?

Regards,

[perkster]

its doubtful ITlover, if it is a DNS problem and not the website in question its most probably to do with firewall settings or your DNS servers.

the IP address i used in other threads to help people with suspected DNS problems is:
64.233.161.147

its just one of a few IP addresses that google uses. if you put that address in the address bar of your browser and you see a google page, but when you type in www.google.com and hit return and you don't then you likely have a DNS problem.

this is because when you type www.google.com in the address bar, it looks in your local cache
first to see if you have already been there to get the IP address, if no luck it will then try router if it remembers, if not it will send a request off to the DNS server in your TCP/IP settings, which is usually the ones for your ISP provider, it sends a request for the IP addy that relates to www.google.com and the DNS server sends back the IP address, the browser on your computer then connects to that IP address (address on the web) and shows the page.

so you see putting that IP in there bypasses the need for a request to be made to the DNS server, so if your computer can connect to that Ip and display the page, then you are connected to the net and your connection is not blocked etc. if you then type in google.com so it asks the DNS server for that same IP address and it fails, you can assume its the communication or translation from the DNS server that is the problem.

OpenDNS is a free service where they have very fast huge DNS servers, and you can put these server addresses in your TCP/IP settings instead of using specific ones to your ISP or the default ones found through your ISP. since their DNS servers are better and faster and never usually down it can fix probs and speed up many peoples internet experience by translating the addresses of sites faster. but not point switching to their DNS servers really unless you crave that extra bit of speed or ascertain your DNS servers with your ISP are causing your problems.

DNS problems are not hat common in comparison to firewall and other TCP/IP problems and settings being wrong.

are you having problems with specific sites or all sites? try the IP test i mentioned above, i only suggest that IP because googles site is never down, is recognisable easily and its fast to load as its minimal filesize.

[ITlover]

Hello,

So you mean to say that if i am not able to access a website of google by typing www.google.com in the address bar of the browser window ,then it is a DNS issue but if i type the IP address in the address bar and then press enter, then i can access the website www.google.com,which is an alternate temperory solution,right?
but how will I know whether it is a DNS issue or not if we are directly connecting by entering the IP address of the website?

Do u mean to say that the Firewall settings in the DNS Server of the ISP blocks the request for a perticular website if we try to access it?

For example some ISP Services have blocked access to pornal and other unacceptable websites by configuring there firewalls?

Are there firewalls like external devices or they are just like the firewalls that we use in Windows?


Regards,

[perkster]

no, im saying if you type www.google.com in yoru address bar and hit enter you have a web connection problem, could be DNS but doubtful, the only way to know if its a DNS prob is to try the IP i stated above, if the IP works but www.google.com DOESNT then its a DNS problem, if neither work then its not a DNS problem but a general settings or firewall prob.

firewall probs are firewalls on your computer blocking your browser from accessing the net or enough rights, or conflict between two different firewalls can cause problems has nothing to do with DNS or DNS servers, but is highly more likely to be responsible for probs with internet connections.

ISPs dont block you from sites unless you use their parental controls.

most firewalls are software on your PC but most good routers have built in firewalls giving youa firewalled connection

[ITlover]

But Sir,

how can it be a webconnection problem, if i am able to use msn and yahoo chat software?

regards,

[perkster]

simply because a firewall could be blocking your browser but not the programs you mention.

it could also be that a certain port may be blocked which stops http traffic but those programs use different ports so are not effected.

[ITlover]

Hello Guys,

Sorry but sometimes questions strike my mind and i feel like asking.

My other question is that if our DNS cache becomes corrupt ,then will not the request from our computer go directly to the DNS Server of the ISP?

What if some of the websites donot have there domain name to IP address resolutions in our DNS cache, will not the request for such websites go directly to the ISP's DNS Server inspite of our computers DNS cache being corrupt ?

Regards,

[ITlover]

So it means that the request for website access followes a perticular path:

request---->DNS cache---->Router-----> DNS Server

Are there perticular commands like "ipconfig /flushdns" to flush the DNS cache of routers?

Can we keep both the DNS Server settings of the ISP and the Open DNS Server settings in our TCP/IP configuration?


Regards,

[perkster]

you could perhaps try one of each of their DNS servers in your two settings.

usually you can just restart the router through the control panel or unplug it, i think that would clear any cache, but as stated not all routers have a DNS cache anyways