DHCP Lease Time

Hi All,

Merry Christmas to those who were celebrating it.

On a DHCP Scope, the lease duration. If for example, it was set to 6 days, does this mean that if a PC is shutdown for say 1 week, will its IP address not be released until 6 days after the shutdown?

Thanks

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Comments

atorven

The way i've understood it is that at the 6 day mark, if the same client hasn't requested a renewal of the same IP address it will be released back to the general pool, also if I remember correctly, clients will attempt to renew their addresses at the halfway mark, in your case on day 3.

jmritenour

It's six days total, from when the IP was first granted to the client from the DHCP server. As atorven said, if the client doesn't request a renewal and the lease period expires, the IP is released and placed back into the pool.

If the client is powered on and connected, it will by default first attempt to renew its address once the lease period has reached 50% (known as the T1 period). It will then try to renew it's address periodically. If it is unsuccessful, at 87.5%, it will then enter the T2 state, in which it will attempt to obtain a lease from any available DHCP server.

control

Thanks,

Is there a "one size fits all" lease time, e.g 6 days? Is there a situation where you would set the lease time for a few hours? Been a while since I've worked with Servers and DHCP. I'm trying to find ways to increase availability of addresses, and thought that this might be something to try, so PCs that aren't on the network are "hogging" an address that someone else might be able to use.

Amending the current scope subnet is not an option for increasing the address space.

grechy

Fix the bigger problem which is your subnet sizes.

More Vlans or bigger pools

dontstop

control wrote: »

Is there a "one size fits all" lease time, e.g 6 days? Is there a situation where you would set the lease time for a few hours?

A Wireless Network is a good candidate for very short lease times, this is especially prudent where lots of mobile devices are connecting like Smartphones, Tablets & PDA's in both the workplace or in a place that has high foot traffic and short bursty connections (like an Airport Terminal)

jml.

MickQ

As a follow on from the above comments, you need to look at the number of clients and how long they're on your network.

There's little point in giving a lease time of a week to clients in an airport lounge when they're only there for a short period. A lease time of an hour (possibly less) would be better here. This way, the IP is freed up sooner for recycling.

If you have a stable network, with few clients leaving and joining, then you'd assign a longer lease time.

The art is when you have a mix of both. Usually though, you'd have different subnets for wired and wireless clients.
This gives you a bit more flexibility in allowing an SSID for guests/visitors with a short lease, and longer leases for staff devices which are on the network for a longer time.

Qord

6 Days is a really long time. Like, really long. Most of our locations are set to a 3 or 4 hour lease time. We have a lot of people who come in for a few hours and then leave, so there's no reason for us to have a long lease time. In fact, I think that if we had a 6 day lease time most of our sites would run out of IP's halfway through the first day. The quicker addresses get released, the quicker we can hand them out again.