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My webhost's FTP allows connections only from preconfigured IPs or hosts. Since I have a DSL connection that resets the IP every 24 hours I signed up for dyndns.com and got myself a hostname and the FTP has been configured to allow connections from it. It all works fine but there's this time right after my IP changes when the DNS server which the FTP uses didn't pick up the change yet and blocks my connection. Sometimes it can even take up to 6 hours for it to update to my new IP from the hostname.
Do you guys have any tips on how to remedy this situation? Does dyndns have any freely available DNS servers so I could possibly add them to the FTP's configuration?
Answer by Cry Havok · Dec 30, 2010 at 01:11 PM
The time for the refresh is supposed to be controlled by the
TTL set in the record, which for Dynamic DNS defaults to 60 seconds. This means that 60 seconds after your hostname is updated the new value should be visible to all.
Unfortunately some badly behaved DNS servers ignore shorter TTLs and it sounds like the DNS servers that you are using do that. You can confirm that it is the DNS servers by flushing the DNS cache on your PC (
ipconfig /flushdns on Windows). If you still see the old record after that then it is your ISP's DNS servers. To work around that try using another DNS service (such as Internet Guide or Google DNS).
Answer by cgonyea · Dec 29, 2010 at 09:48 PM
This sounds like an update client issue not a recursive DNS issue. If you are using a hardware update client (such as your router), make sure that device has the latest firmware.
If you are using the DynDNS Updater by DynDNS, we automatically check the IP every 10 minutes. Properly written update clients should have a similar schedule.
Answer by nowotnypl · Dec 30, 2010 at 12:26 PM
It's not an issue with the update client because I can see the updated IP right after the change when I login to dyndns.com so this part works fine...
But explain to me one thing: how long would it approximately take for the DNS server that my ISP uses to pick up the change after it's recorded by dyndns... Because from my experience it can take couple hours after the IP change before I can visit my hostname and it takes me to the new IP... I mean, that's how it works, right...? My ISP resets the connection, gives me new IP, dyndns records got updated with that IP and DNS servers around the world pick up the change when they're scheduled to refresh their records which can take a significant amount of time... Or am I missing something...?
However are you sure it's the DNS servers the FTP server are using?
I'm not 100% sure... I guess I would have to ping the host from the server right after the IP change...
Does the host have a local DNS cache?
I don't know... but it probably does...
Answer by nowotnypl · Jan 10, 2011 at 10:19 AM
Thanks for all the replies. I was under the impression that the FTP server checks the IP against the hostname every time a connection is made but after carefully re-reading the documentation it turns out it only does it on the start. So after my IP changes the FTP server should be restarted to pick up the change which isn't really a feasible option. I guess I'll have to find other solution for that. ;)
This means that 60 seconds after your hostname is updated the new value should be visible to all.
Thanks. I always thought it takes much longer. And my view was skewed further by the FTP issue. Now I know the truth. :)