DNS records that are 2 months old? [closed]

Question

I moved my app 2 months ago to a new server and did a new release. I just get an email form a customer saying a link isn't working.

It looks like he was on my old site. I checked the logs. The app is still online but has no name.

So how is it possible that a client has DNS records that are more then 2 months old? Is this normal and what should I advise to do?

Thanks

Answer 1

This is not normal and nonstandard behavior.

Usually all the DNS servers should adhere to the TTL (time to live) of a DNS record and fetch it anew if the time has elapsed. And since all the other customers can access your application fine, your DNS records should be alright and way below the 2 months in terms of TTL.

1. Let him restart his router by unplugging and replugging it. The router might be the instance which caches the DNS wrongly (very likely since home routers sometimes have sloppy firmwares. Errors like this probably would not happen in large DNS servers, compared to the multifunctional SOHO routers)

2. You could suggest him to change the DNS server his computer uses to 8.8.8.8 and 8.8.4.4 (Google's DNS servers which listen to the rules).

3. If he is in a company, tell him to report the DNS caching error to his IT administrator, he should know what to do.

Answer 2

This is, sad to say, normal and quite standard …

… if you did what so many people do and switched content DNS service from one host to another but omitted the vitally important step of ensuring that the old host published the new domain delegation data. The way that DNS works means that its possible for people, who look up your domain names often enough, to be querying the DNS server on the old host indefinitely. There's nothing nonstandard or erroneous about this. There's no problem with caches, TTLs, routers, administrators, or any other people's DNS servers apart from your own. The DNS is working as specified. It is simply that, as specified, things can go wrong this way if you don't do switchovers correctly. (The DNSSEC people have recently discovered that DNSSEC amplifies the problem, especially if the people running the old content DNS servers choose not to coöperate.) This is why comprehensive instructions on switching DNS hosting services always point out the necessity of this step.

Of course, this is assuming that this is anything to do with the DNS in the first place. The idea that your client has two month old DNS information is sheer guesswork on your part. You haven't even checked with the client as to what DNS information xe actually has. Collect data and diagnose the problem first, before handing out spurious advice to customers to do random things to their machines.

Further reading

• Jonathan de Boyne Pollard (2003). How to switch a domain from one set of content DNS servers to another: Changing the delegation that the old content DNS servers publish. Frequently Given Answers.
• Jonathan de Boyne Pollard (2004). Prove that your problem really is a DNS problem.. Frequently Given Answers.
• P. Koch and M. Sanz (2011-10-31). Changing DNS Operators for DNSSEC signed Zones IETF Drafts.