Slow first name resolving

Question

Hi,
This is the situation: Windows 2012 R2 servers, multi homed with a back-end and front-end NIC.
The back-ends are attached to a back-end network (10.1.0.0/8) where two AD servers are running (10.1.0.1 and 10.1.0.2). The front-end interfaces are attachted to an monitoring network 10.254.0.0/8). The servers get their IP and DNS settings from the AD servers.
The AD servers are in domain 'test.net.'
The backend interfaces are configured with DHCP and the DNS servers are given in the advanced properties of the IP4 configuration of those interface. The setting Register at DNS server is marked.
The frontend interfaces have static IP addresses, no DHCP configured, no DNS servers configured and the setting Register at DNS server is disabled.
If we do a ipconfig /flushdns on one of the servers, immediatly followed by Measure-Command { ping -n 1 server01 }  (where server01 is registered in AD as server01.test.net and is a different server then the one tested on) it takes almost 3 seconds
before the reply is finished. After that, when the local DNS cache is filled, it only takes 38 milliseconds.
The question is what is happing. We've disabled all DNS settings on each interface, apart from the backend interfaces, but it still looks as if DNS is sort of circulating around the interfaces to find a suitable DNS server. I've even take a look in the registry
(system/services/tcp) and it looks good: only one DNS binding to the correct interface object.
Does anyone have some idea what causes this?
Tia
John Lasschuit

Answer 1

Hi John,
Based on your description, my understanding is that you are wondering why the name was resolved slowly at the first time.
In general, the DNS query process occurs in two parts:
A name query begins at a client computer and is passed to a resolver, the DNS client service, for resolution using locally cached information.
When the query cannot be resolved locally, DNS servers can be queried as needed to resolve the name.
The local resolver cache can include resource records obtained in answered responses from previous DNS queries are added to the cache and kept for a period of time.
So caching provides a way to speed the performance of DNS resolution.
For more details, please refer to the article below,
How DNS query works
http://technet.microsoft.com/en-us/library/cc775637(v=WS.10).aspx
Best Regards,
Tina
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