Information Technology Reference
In-Depth Information
You can also use this same technique to set the TTL for an individual resource record. For
example, to change the A record for server trey-wds-11 to have a TTL of two hours, use the
following:
$NewRRObj = $OrigRRObj = Get-DnsServerResourceRecord -Name trey-wds-11 `
-ZoneName TreyResearch.net `
-RRType A
$NewRRObj.TimeToLive = [System.TimeSpan]::FromHours(2)
Set-DnsServerResourceRecord -NewInputObject $NewRRObj `
-OldInputObject $OrigRRObj `
-ZoneName treyresearch.net `
-PassThru
HostName RecordType Timestamp TimeToLive RecordData
-------- ---------- --------- ---------- ----------
trey-wds-11 A 0 02:00:00 192.168.10.11
Round robin load balancing is an easy and unsophisticated way to distribute load across a
group of servers that provide the same service. The basic process is to create A or AAAA
records with the same name pointing to each of the servers in the round robin. By default,
round robin is enabled on Windows Server 2012 R2 DNS servers. If the service uses an SRV
record, the SRV record should use that A or AAAA record name in the Host Offering This
Service box.
Each time a new client requests the service or server, the DNS server returns one of the IP
addresses that matches the host name queried. After clients have cached the DNS informa-
tion locally, they usually won't need to request it again until the record they've cached ages
out. But different clients get a different IP address in the round robin group.
Windows Server also uses netmask ordering to attempt to connect to the service or server
that is closest. This proximity awareness is used to return the A or AAAA record whose IPv4
address is in the same subnet, or whose IPv6 address has the longest prefix match. When
both netmask ordering and DNS round robin are enabled, round robin load balancing might
not always return a load balanced address.
Another option you can configure for resource records is what type of update is permitted. By
default, Active Directory-integrated zones are set to allow only secure dynamic updates. When
DNS records are created or updated by a Windows DHCP server, the update automatically
updates the A or AAAA record and the PTR record. It can be further configured on the DHCP
server to enable DHCP Name Protection. If DHCP Name Protection is enabled, the DHCP server
attempts to register the A or AAAA and PTR records for the client, but if a different client
already has the name registered on the DNS server, the new registration will fail.
