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Internal DNS issue, internet is too slow

Mazaya Support
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I have issues with my internet as it is very slow in the office, suspecting something wrong with the internal DNS server as when added ISP DNS address, it is working fine, but facing issues to access the internal servers and published applications.
How can i find out the issues in internal DNS
Required urgent assistance
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Shabarinath RamadasanInfrastructure Architect

Commented:
Hello,

Is the name resolution happening from the client if you try using nslookup?
Is there a timedelay in name resolution happening from client machine when compared to do the same exercise with ISP DNS?

If yes - Then how many DNS IPs are configured on each client machine?
If there are multiple DNS IPs, do the same exercise to do an internet name resolution by setting specific server in nslookup.
This will make it clear that entire DNS has the same issue or if it may be an issue with one of the DNS server configured.

Ideally, if one among the multiple DNS server is responding or having issue to handle client request - there is a timeout value which is configured on the client network interface for sending the same query to the next available DNS . By default, its 3 seconds.

For example, my client has three DNS IPs configured on the network interface.
If there is a query for name resolution and its not available in the local DNS cache, the request needs to be routed to the first DNS.
Client will wait for 3 seconds. If no response from first DNS, the same request will be send again to the second DNS.
Client will wait again for3 seconds. If no response from the second DNS, the same request will be send again to the third DNS.
Client will wait again for 3 seconds. If no response from the third DNS, client will fail to that request.

If you can provide more clarity on the configuration - I think we can isolate and fix it.

Cheers !

Author

Commented:
Hi Shabarinath,

Please find below our comments,

Is the name resolution happening from the client if you try using nslookup?   Yes
Is there a timedelay in name resolution happening from client machine when compared to do the same exercise with ISP DNS? No

If yes - Then how many DNS IPs are configured on each client machine?  Before it was two (Both internal), but now added ISP DNS as the third one)
If there are multiple DNS IPs, do the same exercise to do an internet name resolution by setting specific server in nslookup.
For internal addresses  name server is getting resolved, but for the ISP one it giving request timed out message.
Commented:
if you are using Domain DNS...
just go to Domain DNS settings
add ISP dns in dns forwarders it'll resolve...

then just add your Domain DNS ip on clients that is enough ..you domain DNS will take care of it...

check the following link

https://www.experts-exchange.com/questions/29162896/Internally-resolving-a-domain-works-outside-our-DNS.html?searchSuccess=true&searchTop10=true

all the best

Author

Commented:
Thanks to both Shabarinath and Sajid