DNS Settings: Start of Authority Window: Refresh Interval, Retry Interval, etc....

What do these things mean in the Start of Authority tab in the properties window of a forward lookup zone?

Refresh Interval

Retry Interval

Expires after:

Minimum (default) TTL

TTL for this record

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feptiasConnect With a Mentor Commented:
Here is a copy of some notes I made on this subject (it is largely taken from Mark Minasi's excellent book Mastering Windows Server 2003). Might be useful to JJ when he is revising too!

In conventional DNS, the Primary DNS server is the only one that can accept changes. Secondary DNS servers hold a "read-only" copy of the records on the Primary. However, when AD-Integrated zones are used, the notion of primary and secondary DNS servers is eliminated and, in effect, all DNS servers can accept changes for those zones. In this mode, a multi-master replication model is used.

Where the conventional Primary and Secondary server model is used, something has to trigger the copy process whereby the secondary server gets updates from the primary. This process may be referred to as replication of the zone files because most DNS servers store the zone data in text files that follow a convention in terms of their internal format. Events that will trigger zone replication in Windows are:
1) When the secondary server starts
2) When a zone transfer is forced using an administrative request at the secondary server
3) When the zone data expires
4) When the Primary notifies the secondary that it needs to update (RFC 1996)

Zone data is considered to have expired - the third case in the list above - when the secondary sees that the serial number (stored in the SOA record on the Primary server) has changed since the last time it looked. The secondary will look at the serial number at regular intervals as defined in the Refresh Interval in the SOA record on the primary server. It is the equivalent of a polling interval.

If the secondary doesn't get a response from the primary, it will try again at intervals defined in the Retry Interval as stored in the SOA record on the primary server.

If the primary continues to not respond then eventually the secondary will regard its data as out-of-date and it will discard it. The time it waits before discarding data is set in the Expires After parameter as stored in the SOA record. After this time, where the secondary server has not been able to contact the primary, then the secondary will no longer be able to answer name resolution queries for that zone.

Jay_Jay70Connect With a Mentor Commented:
Hi oxygen_728,

refresh interval
Specifies the refresh interval for the zone. The standard setting is 900 (15 minutes).

retry interval
Specifies the retry interval for the zone. The standard setting is 600 (ten minutes).

TTL (Time to Live)
specifies how many more hops a packet can travel before being discarded or returned

Expires after
Amount of time until the data packet expires

TTL for this record,
you specify how long the data record is around till it expires

taken from technet and google
oxygen_728Author Commented:
Well... I'm not knowledgable enough to understand fully what you just posted Jay.

What exactly is the refresh interval for the zone?, retry interval? Why are packets involved with DNS settings?
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Jay_Jay70Connect With a Mentor Commented:
DNS provides data packets containing name or IP records, when a request is made to a DNS server for a name, it comes in the form of a data packet, when the request is responded to, the dns sends the answer back in a packet,

if a packget gets lost or loops, then the TTL expires it so it doesnt forever float around causing traffic

Refresh interval is how often the zone refreshes itself for new records and updated info etc

retry interval is how often the dns server tries to find its records from elsewhere if it fails to find a record locally

(its been a while since i studied DNS so i apologies if my answers arent great)
oxygen_728Author Commented:
Do you know if refresh interval is internal and retry interval is external? They seem pretty close to the same to me.

is the TTL for the record referring to how long the current DNS information on my DNS server is valid once it is retrieved by other DNS servers?


i am to far out of it to give an accurate answer on the details, as i mentioned its been a while and the deffinitons were basically straight from technet
oxygen_728Author Commented:
Ok thanks for the info Jay, You'll get some and probably most of the points =)

I appreciate your time
no no its not about points, if someone gives you a better then they deserve them, im trying to refresh myself for latet MCSE exams so i need to be learning all this again anywayz :)  see if you can grab Chris Dents attention   he is a DNS Guru
feptiasConnect With a Mentor Commented:
On the TTL parameters, unfortunately JJ70 is incorrect when he describes it as a limit on the number of hops a packet can travel. There is a TTL on TCP packets that is like he described, but the TTL on DNS records is different. It is measured in days, hours, minutes and secs, not in number of hops. (TTL = Time To Live as already mentioned).

When DNS servers have to go and ask other DNS servers for the answer to a query, they will normally cache the answer to reduce the traffic should the same query get asked again. The TTL value on a DNS record determines how long other DNS servers should hold it in their cache before assuming that it is too old to be relied on. Once that time limit has been exceeded the DNS server will re-query the original source to make sure it has current information. This is the mechanism that can cause newly created DNS records (such as MX records for example) taking several hours to dissipate throughout the DNS world.

In an SOA record, the value for "Minimum (default) TTL" is the default value that will be used whenever a new record is added to that zone. Each record can be given a different value from the default if you choose, but if you click, say, New Host (A) record, you will see that it starts out with the default as already set in the SOA. Even the SOA record itself has a TTL value and that is shown in the parameter "TTL for this record".

Hope this answers all of your question.
hmm taken straight from technet so debate it with them :)
Perhaps you were looking in the wrong part of technet. This is the definition I just found:
Time to Live for Resource Records

A resolver caches the information it receives when it resolves queries. These cached responses can then be used to answer subsequent queries for the same information. The cached data, however, has a limited lifetime specified in the Time To Live (TTL) parameter returned with the data. TTL makes sure the DNS Server doesn't keep information for so long that it becomes out of date. TTL for the cache can be set on the DNS database (per individual RR by specifying the TTL field of the record and per zone through the minimum TTL field of the SOA record) as well as on the resolver side by specifying the maximum TTL the resolver allows to cache the resource records.

actually looking through history i think my TTL deff came from wikipedia of all places, my apologies
oxygen_728Author Commented:
Thanks to both of you for your time
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