Steps to change DNS Servers options in DHCP

What's the best way to switch to another DNS in DHCP server?  
Lower lease -
Change scope options 006 DNS Servers  - reboot
Sounds right?

Is there a way to do it transparently without a boot?
LVL 17
Tiras25Asked:
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Cliff GaliherCommented:
If you want to do this quickly then you'll probably need to trigger reboots or remote ipconfig /release ipconfig /renew commands.

Lowering the lease time helps for a long term planned transition (such as changing ISPs or entire address schemes), but *existing* leases will still have the time and may not try to renew right away.  So quick changes require processes outside of DHCP itself.
Tiras25Author Commented:
Got it.  The issue most devices aren't windows.  So ipconfig /release  /renew wont work.  VoIP phones for example.
Yes, if I lower the lease its also required a reboot.  Otherwise devices/clients won't know the lease is lowered.
Changing the DNS Servers options also requires reboot..
nociSoftware EngineerCommented:
If you lower the lease, the new lease time will be in effect after the leases are replaced.
Lease prolonging should be done between halt of lease time and lease expire. (most do after half lease time).
The lease is NOT an immutable constant..., it is sent with each DHCP negotiation.
So no reboot should not be required.. unless you want to FORCE change ahead of time.

BTW, setting a lease time of 1-2 hours would be perfectly usable to anyone, not too many changes and not too long to change.

Another way to trigger DHCP upgrade MAY be unplugging/replugging computers.  Or the digital equivalent of this disable/pause/enable switchports.
Tiras25Author Commented:
Thanks noci!  I lowered the lease time on the scope.  However, the Lease Expiration still stays the same.  Unless I reboot the device.
So looks like he device wouldn't know about the lease expiration until booted.
nociSoftware EngineerCommented:
If you change the lease time then ONLY the server knows of the new lease time until the NEXT lease gets issued.
Current leases wil not be affected, after renewal (Typicaly around half the lease time) the new lease time will be seen by the client. As well as other settings.
(DHCP is completely client driven, just like DNS TTL), the address is reserved only for the duration of the lease, so the server can do NOTHING with the address (or attached info)  until the client restart a negotiation.... if ever.   Client SHOULD refrain from using the address after the lease expires.. (not all systems do..., so most DHCP server check if an address is still unused BEFORE reissuing  and address).

it might be wise to use short lease times (30 minutes) when everything is in flux, giving sufficient freedom to changes and and long enough stability.
Same for DNS change periods, set TTL to 300 seconds or so, and raise again when things settle down.

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Windows Server 2012

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