Do the IP addresses have to be in the Class C 192.168.???.??? range? What router are you currently using?

As for routers, both of which I use, the DrayTek Vigor2862 family and Ubiquiti EdgeRouter X can allow large DHCP pools and short DHCP lease times.

For the EdgeRouter X you will need an external WiFi AP. If you get the appropriate member of the Vigor2862 family the WiFi AP will be built-in.

But how big a pool can you actually have? I can set the pool starting and ending addresses on my Zyxel router but I found that the first 24 bits of the IP addresses have to be the same. The router changes what I enter and its own IP address to ensure that it conforms.

Draytek 2862 and 2926 certainly do on lan 1-3. Up to 1022 per subnet.

In reply to a post by Michael_Chare:

But how big a pool can you actually have? I can set the pool starting and ending addresses on my Zyxel router but I found that the first 24 bits of the IP addresses have to be the same. The router changes what I enter and its own IP address to ensure that it conforms.

I don't know as I've not tried. Given the router lets you change its own IP and subnet mast, it is possible it supports larger subnets than /24.

The ASUS range certainly supports hundreds of thousands of connections through the NAT table. (300,000 or more).

I've been puzzled since this thread was started.

If the devices are being sent out after being configured, at a guess something like CCTV cameras or associated kit like "Ring" remote video doorbells, the problem with local DHCP/NAT seems to be the storing of MAC addresses and the table filling up. Not the number of IP addresses itself.

I've just googled about MAC aging time as it isn't something I have seen as settable on my domestic level routers. Not that I've been looking.

A Juniper article. Cisco has similar.

Am I barking up the wrong tree?

In reply to a post by RobertoS:

Am I barking up the wrong tree?

Sort of, you've conflicted two topics, because home routers have in one box multiple functions, network routing, NAT, DHCP server, DNS proxy, network switch etc. Each one of these handles things independently despite being inside the one box.

The Juniper article is about switching, where the MAC table associates a hardware device with an IP address in able for the switch to work. Generally this is not a problem as switches can remember hundreds of addresses and IPs and the switch ages out ones not seen. Juniper switches don't generally do DHCP (although they are insanely flexible and you probably could).

The problem in this thread is related to DHCP, which separately holds a list of MAC addresses that request an IP. When the pool of IPs is exhausted, no new devices (new MAC addresses) can get issued an IP.

The answer is to reduce the "lease duration" so that the DHCP server releases addresses back to the pool quickly.

Others have suggested enlarging the network subnet, so that more than 250 addresses can exist in the DHCP pool. Something that is very easy if you use Windows, Linux or another OS to run DHCP - is not obvious if you are trying to use home grade routers.

Edited by jchamier (Sun 13-Jan-19 16:51:36)

Ah, thanks .

It still comes down to the releasing though, as mentioned in the OP. Given the "hundreds per week", maybe the answer is simply a weekly or even daily factory reset of his router and re-loading of a pre-saved config?

OP here.

Thanks for the suggestions. I'll look into the Draytek 2862 and ER-X devices.

I've been looking to increase the pool size and/or reduce the lease duration.

I want to avoid a daily reset to clear DHCP allocation tables.

Good luck bsdnazz, hope you find a solution that works for you

If he can reduce the lease time to 15 or 30 minutes, the problem will go away.

A reboot probably doesn�t clear the DHCP tables, reloading configuration might but will depend on the make.

Have to test.