Why information from DNS become unavailable?

Question

I study in I.T., and I want to get better in troubleshooting skill. This morning I was disconnected from Internet, indicated by the link light on my modem router uncolor (no green or even red). The link light for DSL was solid green. I ran Windows Troubleshooting for network connection and it stated that the information for DNS was unavailable (In Event Viewer, the error code is 1014). The way I solve the problem was first I flushed the DNS and then register it on the Command Line. That didn't solve the problem, so I just turned off the router and then turn it back on, which fixed the problem. Now I want to know why did the problem occured? What caused it?

Answer 1

Barry M had it right, why 2 thumbs down?



So the problem was in your modem/router. Flushing the DNS did nothing as well as running Windows Troubleshooting which is worthless (except for driver problems). It is hard to debug because it

is an integrated unit.





First thing, ping the default gateway. If it responds, you know that the router portion is at least up.



I usually ping 8.8.8.8 which is google's dns/ping server. If it pings, then you know your network

is good. If it doesn't, then something is amiss. Since you give the address as an IP, you know

this has nothing to do with DNS because DNS isn't called.



If that worked, I'd run 'tracert 8.8.8.8' and see how far it gets. If it doesn't get pass your modem, then the ISP is broken. Get on the router/modem through the admin interface, and release and renew your external IP.

If it doesn't renew, you have a problem, you aren't talking to the ISP.



If tracert goes beyond your modem and ISP, they you can debug it further (dns server might be down or some routers run a dns cache process that might be down, some just give you the ISPs ones).



Run tracert and record the path when it is working so you are familiar with it. The last hop

should be like:



8 google-public-dns-a.google.com (8.8.8.8) 2.094 ms 1.934 ms 2.125 ms



Learn to query the DNS directly, like:



# nslookup - 8.8.8.8

> www.yahoo.com

Server: 8.8.8.8

Address: 8.8.8.8#53



Non-authoritative answer:

www.yahoo.com canonical name = fd-fp3.wg1.b.yahoo.com.

Name: fd-fp3.wg1.b.yahoo.com

Address: 98.138.253.109

Name: fd-fp3.wg1.b.yahoo.com

Address: 98.138.252.30

>



Do the same with the DNS server you are given.

Answer 2

This sounds like the ISP's server was down.



DSL ISP connections occur at two levels:



First the low level broadband connection is established. This happens when the circuits in the modem recognise and establish connection with the equivalent circuits in the ISP's end of the line to your modem. When this is established, you have a working DSL connection that is capable of passing data, and the DSL light indicates this.



The second level requires a client device (normally your router, but it could be a single computer if no router is available) to log on to the server at the ISP. Normally, a username and password is required although this varies for different ISPs. This is indicated by the link/Internet light. The actual colours vary for different makes of equipment.



Once the login is successfully completed, the client device uses DHCP to request the required addresses - your public IP address, gateway address and DNS server address(es).



If the router fails to get the addresses (because it failed to logon to the ISP's server), then any requests for DNS information from a computer connected to that router will fail.



The diagnosis normally involves logging on to the router itself and going to its status page or connection log. The status page will normally show the addresses that have been assigned by the ISP. The connection log will normally show some form of login timeout with the ISP.



I hope this answers the question.

Answer 3

An issue with the modem. Happens all the time. Not necessarily DNS. DNS is what it looks up to find a website but if there no internet then none of it will work. Also very common for DSL to go out constantly. I've used had DSL twice in my life and both times crappy service. Never again.

Answer 4

The reason this happens is most ISPs keep a close eye on bandwidth, but they don't keep up their DNS servers, and they are often overloaded with too many requests for the server(s) to handle.

Answer 5

Yep, it was your Router, which is why IT Support ALWAYS start by saying 'Have you tried turning (everything) off and on again ?'



Fact is, modern kit and software is so complex that it can't ever be totally debugged ... problems (like memory leaks, untimed out open connections etc etc) accumerlate gradually and evetually the kit crashes ... all they can 'guartantee' is that "It works OK when it's truined on" (so just turn it on again..)..



In the 'good old days', even mainframes would reboot every night == and even today many Routers have a bult in 'reset timer' that reboots them at midnight (or some other time you can set) for this every same reason ..



NB As usual MS Windows 'error' complaints are useless at indicating the real problem ... fact is, DNS is just the first thing that happens when you try to visit a web page, so what 'DNS error' realy means is "Internet not responding" ..

Answer 6

The DNS server could be down