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.
Who is Participating?

[Product update] Infrastructure Analysis Tool is now available with Business Accounts.Learn More

I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

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.
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).
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
Determine the Perfect Price for Your IT Services

Do you wonder if your IT business is truly profitable or if you should raise your prices? Learn how to calculate your overhead burden with our free interactive tool and use it to determine the right price for your IT services. Download your free eBook now!

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.
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?
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.
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:

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

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today

From novice to tech pro — start learning today.