SP4 changes DNS name resolution
After Windows NT 4.0 SP4 is installed, the DNR sends a DNS query to the first DNS server(s) address configured in all of three possible lists. If no response is received within 1 second, the DNR requeries the first DNS server(s) and sends the same query to all other DNS server addresses configured on the client. If the DNS resolver does not get aresponse from any DNS server within 2 seconds, it resends the query toall DNS servers configured and waits for 4 seconds. If no response is received, the DNR resends the request again to all DNS servers configured and waits for 8 seconds. The total delay for DNS name resolution timeout is now 15 seconds.
Depending on the name being resolved, it may repeat the process adding the domain name configured on the client and devolving the specified domain name two labels deep. Also if DNS fails and NetBIOS name resolution is used an additional 3 seconds can be used.
The DNS server(s) queried from these 3 possible DNS Server lists:
- Static (configured through Control Panel)
- DHCP (obtained through all DHCP-enabled Adapters)
- RAS (obtained through dial-up networking)
A new (post SP4) version of the client DNR, which adds a 0.5 second delay between querying different DNS servers, is available. This allows strict adherence to the DNS search order, but adds (N-1)*.5 seconds to the overalltimeout delay, where N is total number of DNS name servers configured on the client. With this fix the total time spent on DNS name timeout useS the following algorythm:
Depending on the configuration the total timeouts for a particular query can vary from (1+2+4+8=15) seconds to at worst (0.5+0.5+1+0.5+0.5+2+0.5+0.5+4+0.5+0.5+8=19) seconds. For additional information, please see the following article in the Microsoft Knowledge Base:
Article ID: 198550 - Last Review: 02/21/2014 00:31:21 - Revision: 2.2
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