[CentOS] OT Advantage of running DNS server?

Tue Jun 23 13:25:41 UTC 2015
James B. Byrne <byrnejb at harte-lyne.ca>

On Mon, June 22, 2015 08:14, Timothy Murphy wrote:
> What is the advantage, if any, of running one's own DNS server?
> Surely the link between domain name and IP address
> must already have been established?

Response time.

If one does not possess delegated authority for ones own forward zone
or for the IP address block reverse zone, and thus must operate an
authoritative server somewhere even if through a third party, then one
runs a DNS server to quickly respond to internal lookup requests.  A
very common case is running a recursive DNS service on a MicroSoft
Active Directory Domain Server.  This gives all of the workstations in
that domain, assuming that they are conventionally configured, a
single lookup to small number of known and trusted servers to resolve
all unknown dns addresses on behalf of the client.

Once a lookup is successfully resolved then that data is customarily
cached in the local dns server for the Time To Live value associated
with the A/AAAA RR obtained.  Future requests for the same fqdn for
other clients on the same network are then served from the resolver's
cache.  Since it is quite commonly the case that users on a single
domain are accessing the same domains this reduces the time to obtain
an answer for subsequent requests from different clients and the
overall load on the dns infrastructure.

There are some services that are particularly sensitive to DNS
resolver time.  SMTP MTA and MDA services are notoriously sensitive to
DNS delays and configuration errors.  It a standard practice to run a
caching only DNS resolver service on SMTP MTA's simply to answer
requests generated by the HELO/EHELO verification processes.  A
caching only resolver does what its name implies. It only handles
requests generated on the local host and it caches those answers for
future reuse by that host.

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