Question : Understanding technical terms in DNS

Hi friends !

I am exploring DNS on Windows Server 2003. I want to understand these technical terms in DNS and what is their significance. And also, how DNS works in co-operation with DHCP and WINS.

If it seems more time consuming then please provide some web links where I can find detailed explanation of DNS.

Please look at the snapshots that I have attached.

Regards.

Answer : Understanding technical terms in DNS

Aging and Scavenging:


These are used to keep a dynamically updated DNS zone clean of stale records.

Each dynamically registered record has a TimeStamp value set. You can see that value if you select View / Advanced and open the properties for a record. If a client is active it will Update / Refresh that record, resetting the TimeStamp each time. MS DHCP does this on behalf of clients by default.

A stale record is one where both the No-Refresh and Refresh Intervals specified above have passed without the TimeStamp changing. The Scavenging process goes through the DNS zone and removed any record which is stale.

Manually created records do not have TimeStamp values and are not subject to Scavenging.

There's a good article on configuring Aging and Scavenging here:

http://blogs.technet.com/networking/archive/2008/03/19/don-t-be-afraid-of-dns-scavenging-just-be-patient.aspx

It covers how it works as well so should give you a good overview.


Zone Properties - The Start of Authority (SOA) Record:


The values you see here are used in a few situations.

First Dynamic Updates. When a system wants to update DNS it must locate a writeable copy of the zone. In the non-AD model that means the server listed as the Start of Authority (Secondary Servers are Read Only). So the client looks up the SOA record and sends the update there (a "please add my name to the domain.com zone").

If you have an AD Integrated Zone you should notice that the SOA record is the DCs name on each server you visit. That is, DC1 will list DC1 in the SOA, DC2 will list DC2, and so on.

The SOA is also used when you have a Secondary DNS Server. It defines the following values:

Serial Number - A version number which is incremented after each update. A Secondary Server would check this to determine if a Transfer is needed to update it's own copy of the zone.

Refresh Interval - How frequently the Secondary server checks for changes to the zone.
Retry Interval - If a Zone Transfer fails, how long the Secondary server will wait before trying again
Expires After - How long a Secondary server will keep a zone (without updates / transfers) before it is considered invalid.

Noite that the SOA record is not used to handle how AD Integrated Zones are replicated.

Minimum TTL (Time To Live) in the case of MS DNS is how long a remote system will cache a reply for. That is, if I look up "www.domain.com" I will keep a copy of it in memory for as long as the TTL tells me to. I will use the version I've remembered for that long, only asking your server again when I forget.

This TTL, or memory timer, applies to DNS servers as well. If the server you use to resolve names asks for www.experts-exchange.com it will be remembered for 3 days, that's because the TTL for this site says to do so.

Responsible Person is an e-mail address, where you would replace the first period (dot) with an at (@). It's not updated all that frequently (nor correctly used often as it should be), and isn't important for internal domains, only really of use for public domains.

HTH

Chris