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Router not releasing/reusing IP addresses?

R7000 is set to "Use router as DHCP server" with starting address as ....2, ending at ....254 with only 3 of those reserved (2 printers & a server... which we've had no trouble with).
We have a handful of workstations connected most all the time & then we connect many different devices for a limited time (1 hr?) during a setup process. We hit a point today where no more devices could connect. Someone powered router off & back on.

Once a device connects & is assigned an ip address, then that device disconnects... does the router hold on to that ip address (not making it available to assign to a newly connected device) for any length of time?

The theory is that after we'd connected so many devices & used up available ip addresses - & then disconnected those devices - we couldn't connect the next set of devices because no ip addresses were available.

I can't find any setting to control this, but I tested a little... Looked at one connected device on the "attached" list, disconnected it & refreshed the list, & it disappeared from the list. Reconnected same device & refreshed the list... it came back up with the same ip address it had before. This was not the first available ip address in our range. Does this mean that it holds this ip address for this device for some length of time - for quicker connection next time? (It was faster connecting.)

This leads me to other questions, but I don't want to sound even more clueless! Hopefully, someone can get me thinking/looking on the right track to figure this out.

Thanks!!
Message 1 of 8
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Retired_Member
Not applicable

Re: Router not releasing/reusing IP addresses?

Most modern clients like Windows will renew the address they were using previously by skipping the first couple of steps in the DHCP process. As long as there is not another device using that IP, the DHCP server will simply assign the same address.

At any rate, it's usually the client that initiates this behavior, not the router/DHCP server.
Message 2 of 8
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Mentor

Re: Router not releasing/reusing IP addresses?

First - it IS possible if you have a very dynamic (in a state of constant change) network to run out of available addresses, even when the total number of devices connected is much less than the number of addresses in the lease pool. Second - when a device is disconnected & reconnected, it will typically request the last used ip address and where ever possible the DHCP server will accede to that request - the most common scenario for a refusal of this request is where the device has last been used on a network with a different address, for example, a laptop or mobile device being taken from work to home & vice versa. Should the device request an address which the DHCP server has marked as leased in it's database, the DHCP server will of course refuse (this is the second most common scenario). Third - yes - once the DHCP server leases an address, it will not offer that address a second time until the duration of the lease has expired - OR - the client releases the address, essentially saying I no longer need the address - if you just power off or disconnect the client that lease will remain active (and unavailable) for the remaining period of the lease duration I have no idea what the lease duration on the R7000 is, or if it is adjustable - some servers default to 24 hours, some to 8 days - if it is adjustable, reducing it may be one way to resolve your problem, the other is to release the address before disconnecting. I have to ask this question though - you say many different devices - exactly how many devices are we talking about? With the situation you describe, you'd have to be connecting well over 200 devices to run out of available addresses - not exactly a residential network scenario.

Give a man a fish, feed him for a day
Teach a man to fish, feed him for life.
Message 3 of 8
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Aspirant

Re: Router not releasing/reusing IP addresses?

Thanks so much for the quick replies!

<>

Yes, this sounds like what is happening.

<<...exactly how many devices are we talking about? With the situation you describe, you'd have to be connecting well over 200 devices to run out of available addresses - not exactly a residential network scenario >>

True... not exactly a home setup Smiley Happy. The size of this office had me on the fence when choosing latest router. There are only have a handful of computers (Windows clients) & a couple of printers attached all the time. However, there are projects involving the set up several hundred devices (usually Apple). Typically it was up to 20 or so at a time, but this time it's getting up to 40 or 50 at a time (each device taking maybe an hour).

<< once the DHCP server leases an address, it will not offer that address a second time until the duration of the lease has expired - OR - the client releases the address, ...- if you just power off or disconnect the client that lease will remain active (and unavailable) for the remaining period of the lease duration. I have no idea what the lease duration on the R7000 is, or if it is adjustable ... if it is adjustable, reducing it may be one way to resolve your problem, the other is to release the address before disconnecting. >>

So... I need to know
a) the setting on the R7000 (is it adjustable &/or what is default duration?)
b) how to release the address before disconnecting an iPad or iPhone

Again, thanks so much for the info so far!!
Message 4 of 8
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Mentor

Re: Router not releasing/reusing IP addresses?

Unfortunately - I'm unable to answer either of those questions. I'm actually in the reverse of your scenario, in a fairly "static" SOHO office, running Netgear's SMB product line - the router I'm currently using is the FVS318N, which does allow for adjustment of the lease duration (default, by the way, is 24 hours - which I suspect may be the same for the R7000), and I don't actually use the router as a DHCP server, that's handled by a Windows 2008 system.

Give a man a fish, feed him for a day
Teach a man to fish, feed him for life.
Message 5 of 8
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Retired_Member
Not applicable

Re: Router not releasing/reusing IP addresses?

Lease time is not adjustable on the R7000 unless you use DD-WRT.
Message 6 of 8
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Aspirant

Re: Router not releasing/reusing IP addresses?

Thanks for both replies. I've considered trying DD-WRT, wondering if there was a good reason... This might be it! I'll also look at the iPads again today for a way to release the ip lease. If it's that simple, we'll make it a step in our setup.
Thanks again!
Message 7 of 8
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Retired_Member
Not applicable

Re: Router not releasing/reusing IP addresses?

There's several reasons to use DD-WRT actually. From all reports I've seen, it's far more stable than stock firmware and doesn't suffer from some of the crippling bugs the stock firmware has.
Message 8 of 8