Why do I need to flushdns?

[doo_much]

OK - so my Vodacom 3G card refused international connections.
Called 082155 and fter spending considerable time being assured that I am a valued client I was connected to a friendly (and yes I was feeling rather irritated) individual that told me to:

ipconfig /flushdns
ipconfig /registerdns
clear my browser cookies (and she didn't know how to do this in FF )

Rebooted PC -> problem solved.

Until it resurfaced again last night. Same remedy worked.

Question is however, what the heck is going on? Is there a way of preventing this from happening?

[doo_much]

OK. From UpdateXP

the DNS Windows XP cache stores BOTH negative and positive entries. The positive entries are those that the DNS lookup was successful and you could connect to the website.

Negative entries are those where the DNS lookup failed and you could not connect to the website.

A problem can arise here because if the DNS cache hold a negative entry and the website you want to view is now OK to view, Windows XP will still give you a DNS error!

Vodacom3G has been cr*ppy for a week - culminating in a message at 082155 this morning saying that their techs were working on the problem.

Sorted.

[Ron2K]

Right, time to bring out the geek explanation here...

To cut down on the number of DNS requests across the Internet, DNS requests are typically cached. Your DNS server will have a cache of all the requests that people send to it, your PC will have it's own (usually far smaller) cache so that it doesn't have to query your DNS server all the time. How long DNS records are kept in the cache depends on the settings of the DNS record you're trying to retrieve; my own experience shows that the TTL values are generally between 8 and 24 hours.

While this does a great job at reducing DNS traffic, problems can creep in when the wrong information is cached, which is what happened in your case. Clearing the cache meant that it would then go and lookup again.

[doo_much]

Ahh I get it - kinda.

And whatever has been/is going wrong at Vodacom means I'm for always caching the wrong DNS info for international sites?

No wonder the poor girl on the support desk
a. Knew what was wrong,
b. Sounded bloody tired!


Thanks UberAdmin!

[shiv]

FlushDNS is useful if you want to cover your tracks
Private Browsing and the like isn't 100% private...

[Anthro]

Download the following app: AnalogueX Fast Cache..
Point your dns server to: 127.0.0.1 as primary, and your secondary to the primary of your isp
Set fast cache settings to use your ISP cache server names... works wonders

[ChuckNorris]

I had the same issue with a client a few weeks ago, nobody on the network could get to Youtube, they experienced the "cache was not able to resolve the hostname presented in the URL".

Originally it was thought to be just one machine, so I did run the flushdns etc commands. Later only were we told that it was the entire network. We run a Linux firewall so we had to flush it there as well.

And Ron2K, I couldn't have explained it better !!! thumbs ups!

We actually had no explanantion for what happened. TTL was one thing but weren't actually sure.

[ADV4NCED]

Question:

If your DNS has cached an incorrect or negative entry, shouldn't re-typing the websites address in with a "." at the end fix or 'refresh' the incorrect entry?

example: www.microsoft.com.