W2K3 DHCP function wrt RFC etc

We have an environment where we wish to have short leases, but have some
devices that may be turned off for a period longer than the lease time.

My understanding of the RFC indicates that the DHCP server should not give
out an expired lease until it has run out of addresses in the scope.

Is this true? Does the W2K3 DHCP service function in this way - or can it be
configured to do so?

Any help is appreciated

"JohnB" <(E-Mail Removed)> wrote in message
news:4E3606EF-D524-4D93-817C-(E-Mail Removed)...
> We have an environment where we wish to have short leases, but have some
> devices that may be turned off for a period longer than the lease time.
>
> My understanding of the RFC indicates that the DHCP server should not give
> out an expired lease until it has run out of addresses in the scope.

Can you point me to the section of the RFC which leads you to this
conclusion? An expired lease cannot be used by a client until a full lease
transaction has been done to re-obtain the lease. Thus, a server is quite
within the RFC to reclaim expired leases at any time for re-allocation to
whichever client requests them.

> Is this true? Does the W2K3 DHCP service function in this way - or can it
> be
> configured to do so?
>
> Any help is appreciated

The Windows Server 2003 DHCP Server will (by default) operate with a 4 hour
'grace period' or 'lease extension' period. This is the time between when a
lease is expired, and when it is actually marked for cleanup. Once a lease
is marked for cleanup (4 hours after expiration, by default), the lease
record will be completely removed at the next cleanup interval (every 60
minutes, by default).

The cleanup interval can be changed by using netsh commands for DHCP Server:
netsh dhcp server <IP> set DatabaseCleanupInterval XX
where XX is the backup interval in minutes.
This setting is stored in the registry, though modifying the setting via
netsh is recommended.

The 'grace period' or 'lease extension' period is also configurable, but
should only be used in very special cases.
You'll need to add a registry value to do so:
Key Location:
HKLM\SYSTEM\CurrentControlSet\Services\DHCPServer\ Parameters
Value Name: LeaseExtension
Value Type: DWORD
Value Data: time in minutes

Hope this helps you out!

--
==============================
Chris Edson
(E-Mail Removed)

This posting is provided "AS IS" with
no warranties, and confers no rights.
===============================

And I almost forgot... You'll need to stop and restart the service for
these settings to take effect.

--
==============================
Chris Edson
(E-Mail Removed)

This posting is provided "AS IS" with
no warranties, and confers no rights.
===============================

"Chris Edson [MSFT]" <(E-Mail Removed)> wrote in message
news:%(E-Mail Removed)...
> "JohnB" <(E-Mail Removed)> wrote in message
> news:4E3606EF-D524-4D93-817C-(E-Mail Removed)...
>> We have an environment where we wish to have short leases, but have some
>> devices that may be turned off for a period longer than the lease time.
>>
>> My understanding of the RFC indicates that the DHCP server should not
>> give
>> out an expired lease until it has run out of addresses in the scope.
>
> Can you point me to the section of the RFC which leads you to this
> conclusion? An expired lease cannot be used by a client until a full
> lease transaction has been done to re-obtain the lease. Thus, a server is
> quite within the RFC to reclaim expired leases at any time for
> re-allocation to whichever client requests them.
>
>> Is this true? Does the W2K3 DHCP service function in this way - or can it
>> be
>> configured to do so?
>>
>> Any help is appreciated
>
> The Windows Server 2003 DHCP Server will (by default) operate with a 4
> hour 'grace period' or 'lease extension' period. This is the time between
> when a lease is expired, and when it is actually marked for cleanup. Once
> a lease is marked for cleanup (4 hours after expiration, by default), the
> lease record will be completely removed at the next cleanup interval
> (every 60 minutes, by default).
>
> The cleanup interval can be changed by using netsh commands for DHCP
> Server:
> netsh dhcp server <IP> set DatabaseCleanupInterval XX
> where XX is the backup interval in minutes.
> This setting is stored in the registry, though modifying the setting via
> netsh is recommended.
>
> The 'grace period' or 'lease extension' period is also configurable, but
> should only be used in very special cases.
> You'll need to add a registry value to do so:
> Key Location:
> HKLM\SYSTEM\CurrentControlSet\Services\DHCPServer\ Parameters
> Value Name: LeaseExtension
> Value Type: DWORD
> Value Data: time in minutes
>
> Hope this helps you out!
>
> --
> ==============================
> Chris Edson
> (E-Mail Removed)
>
> This posting is provided "AS IS" with
> no warranties, and confers no rights.
> ===============================
>
>

"Chris Edson [MSFT]" wrote:

>
> Can you point me to the section of the RFC which leads you to this
> conclusion? An expired lease cannot be used by a client until a full lease
> transaction has been done to re-obtain the lease. Thus, a server is quite
> within the RFC to reclaim expired leases at any time for re-allocation to
> whichever client requests them.
>
You are correct - I attempted to find where I got this from but the current
[and previous] RFC does not say this - I must have been dreaming when I
thought I saw this previously.

Looks like we will need to use longer lease times or static MAC-IP mappings
- doh!

Thanks for you help.