HOTSPOT
Your network contains a DNS server named Server1 that runs Windows Server 2012 R2. Server1 has a zone
named contoso.com. The network contains a server named Server2 that runs Windows Server 2008 R2.
Server1 and Server2 are members of an Active Directory domain named contoso.com.
You change the IP address of Server2.
Several hours later, some users report that they cannot connect to Server2.
On the affected users’ client computers, you flush the DNS client resolver cache, and the users successfully
connect to Server2.
You need to reduce the amount of time that the client computers cache DNS records from contoso.com.
Which value should you modify in the Start of Authority (SOA) record? To answer, select the appropriate setting
in the answer area.
Hot Area:
Answer: 
Explanation:
The Default TTL, is just that a default for newly created records. Once the records are created their TTL is
independent of the Default TTL on the SOA. Microsoft DNS implementation copies the Default TTL setting to all
newly created records their by giving them all independent TTL settings.
SOA Minimum Field: The SOA minimum field has been overloaded in the past to have three different
meanings, the minimum TTL value of all RRs in a zone, the default TTL of RRs which did not contain a TTL
value and the TTL of negative responses.
Despite being the original defined meaning, the first of these, the minimum TTL value of all RRs in a zone, hasnever in practice been used and is hereby deprecated. The second, the default TTL of RRs which contain no
explicit TTL in the master zone file, is relevant only at the primary server. After a zone transfer all RRs have
explicit TTLs and it is impossible to determine whether the TTL for a record was explicitly set or derived from
the default after a zone transfer. Where a server does not require RRs to include the TTL value explicitly, it
should provide a mechanism, not being the value of the MINIMUM field of the SOA record, from which the
missing TTL values are obtained. How this is done is implementation dependent.
TTLs also occur in the Domain Name System (DNS), where they are set by an authoritative name server for a
particular resource record. When a caching (recursive) nameserver queries the authoritative nameserver for a
resource record, it will cache that record for the time (in seconds) specified by the TTL. If a stub resolver
queries the caching nameserver for the same record before the TTL has expired, the caching server will simply
reply with the already cached resource record rather than retrieve it from the authoritative nameserver again.
Shorter TTLs can cause heavier loads on an authoritative nameserver, but can be useful when changing the
address of critical services like Web servers or MX records, and therefore are often lowered by the DNS
administrator prior to a service being moved, in order to minimize disruptions.
http://support.microsoft.com/kb/297510/en-us
http://support.microsoft.com/kb/297510/en-us
https://en.wikipedia. org/wiki/Time_to_live
http://www.faqs.org/rfcs/rfc2308.html#ixzz0qVpTEitk
