HOTSPOT
Your network contains a DNS server named Server1 that runs Windows Server 2012 R2.
Server1 has a zone namedcontoso.com. The network contains a server named Server2 that
runs Windows Server 2008 R2. Server1 and Server2 are members ofan 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.
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 SO
A) 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, has never 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
