DNS problems

[adds21]

Hi there, I'm hoping someone will be able to help me!

We recently changed our internet provider, and therefore had to change our Class C IP block. We run several servers including two DNSs.

I'm pretty sure we did everything correctly when we changed our IP address: We moved over one NS server first, changed the registered IP address at the root servers, moved over all the other servers, and then moved the secondary NS.

For 95% of people, this has been fine. However, we have a few people who can't access our sites, and it turns out the DNS servers they're using can't resolve.

For example, one of the sites we host is cliksoftware.com, if I do an nslookup on this domain from my home internet connection, it works fine and resolves to the new IP (87.102.104.150). However, if I change my DNS servers to ns0.orange.net and ns1.orange.net (these are ones we know we are having problems with), I can't resolve the domain name (eg, a ping will say "could not find host"). Bear in mind we changed IP address about two weeks ago, so this shouldn't be a TTL problem.

If I do an nslookup using ns0.orange.net, then no matter which domain I do the lookup on, I always get refered back to the root servers ("Served by: a.root-servers.net" etc.). This is the only difference I can with the Orange ns servers. Most NS servers will do the lookup themselves and return the IP.

I've checked, by doing an nslookup on the root-servers and the gtld servers that they have the correct IPs for our DNSs (ns0.clikit.net and ns1.clikit.net) - They should and are on the new 87.102.104 class C, rather than the old one which was 195.224.13

I'm really out of my depth here, and don't understand why we're having issues with a few DNS servers, when most are working fine. The only difference I can see is the Orange ones refer back to the root servers.

Can anyone give me any pointers please?! - this problem is driving us nuts!

Thanks.

[Receptional Andy]

Hi adds21,

I would remove the specific references from your question to make it as useful to others in future (a mod probably will if you don't!).

It sounds like a problem with the specific nameservers - if they're are referring to the root servers that's usually because they don't have records for the name mentioned. Are they supposed to be serving these records and other 'public' DNS records?

[adds21]

Hi!

Thanks for the info. The problem is that the problem is specific to certain nameservers. The Orange ones I mentioned for example don't resolve our domain names, whereas 99% of other name servers do. If I use the nameservers I use on my home connection for example, they resolve correctly.

Cheers,
Adam.

[Receptional Andy]

But are the Orange nameservers public? I'm not clear whether they should be responding to requests for other peoples' domain names on those servers. Has your ISP told you to use those servers?

[adds21]

Ah sorry. Yes, the Orange DNS are used if you're connected via the Orange ISP (as I do sometimes on my laptop). We're also having problems with another few ISP's DNSs, although most ISP DNSs resolve the names correctly.

[jtara]

Sounds like a caching problem, which should be reported to Orange. I would expect it to eventually fix itself, as they obviously cannot cache everything forever.

It might help to refresh your DNS entry - easiest way is to simply increment the serial on the SOA record.

If you have a long TTL, you may have to wait a day or two to see changes. It is useful to first lower the TTL in advance of major DNS changes. If you lower it to 5 minutes (in stages, if a large site) then you can very quickly determine if there are any problems once you make the address change(s). Once you are satisfied you can increase the TTL back to 1-2 days.