DHCP Lease Time

A DHCP server has  lease time of 7 days. If a machine retrieves an address should the machine keep that IP even if it is rebooted and even if the DHCP server goes offline within those 7 days? thanks.
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Sid_FAsked:
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savoneCommented:
There is no guarantee that the system will get the same address if it is leased.  Depending on when any of these things occur (reboot/offline) the server can give a new IP address.

A lease is usually renewed at the half way mark of it's lease.  Meaning a 7 day lease is usually renewed at the 3.5 day mark even though the lease is still valid of another 3.5 days.  If the system rebooted inside that 7 day mark it SHOULD get the same IP address.  If the server goes offline just as the lease is about to expire the system will not get a renewal and could pull a new IP address when the server comes back online.

If you need the same IP address all the time, you should consider either:

1) statically assigning an IP address outside of the DHCP pool.
2) Making a DHCP reservation for that system so the server will always give it the same IP address.

Good luck.
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KimputerCommented:
A lease time has no meaning if the machine is rebooted AND the DHCP server is NOT available.
A lease time HAS meaning if the machine is rebooted AND the DHCP has been running fine (no errors or conflicts).
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Sid_FAuthor Commented:
Thanks so I guess the question is why bother setting a lease time outside the default?

So each time my machine starts up it looks to lease a new address but the server keeps track of when the lease expires so hands out the old address? thanks
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KimputerCommented:
Usually, you adjust lease times, in VERY HIGH device rotation network, with hundreds of phones and laptops connecting throughout the day. If you have a "office", with 50 to 100 devices and only a handful of phones, tinkering with DHCP will mostly be wasted effort, the DHCP will "just work" with its default settings for years and years.
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Sid_FAuthor Commented:
What I'm try to allow for is: I have a DHCP server in another site and an IP helper on my local switch. All clients obtain a lease from the remote DHCP server. If the line between the sites when down what would be the impact to my clients
 I know new machines obviously wouldn't get a lease but what happens if
1) A client is already started and within the 7 day lease time nothing should happen even if DHCP is not contactable.
2)If a client with a valid lease time (inside the 7 days) restarts their machine?
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Mohammed KhawajaManager - Infrastructure:  Information TechnologyCommented:
If you are worried about extended outage then either change lease time or implement local DC with DHCP role added.
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savoneCommented:
If the link to your DHCP server goes down

1) Machine just coming on to the network will not be able to get an IP address
2) Systems who currently have a lease will continue to function even.
3) Windows Systems restarted will continue to use their old lease.

See here:
https://technet.microsoft.com/en-us/library/cc958945.aspx

Also, this assumes the link between sites is down for less than 7 days.
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