FPS increased x3/4

[Harry Bloomfield, Esq.]

I originally had several items on my LAN, with fixed IP's configured within the devices themselves, such as an IP cam, routers and printers. Everything else relied on the router's DHCP to allocate an IP, when they connected.

As time as passed and my LAN has become busy with things connected, some things have been unable (despite there being unused addresses), to be allocated an address without a reboot (laptops). I recently added 8x Smart Plugs, which exacerbated the problem, so I thought to try setting up almost everything without a fixed IP, a router allocated IP's.

My main router, which connects to FTTC is runs OpenWRT, which does not allow a reserved section of IP's for static addresses. Rather it seems to use a sort of intelligent reserve, where it DHCP allocates above the static IP's.

Coming to the question now.... I have now set every item which connects to my LAN, either with an IP in the device, or a static address in my router. No more issues with laptops failing to acquire an IP after waking. One thing I have also noticed, is that my IP cam's frame rate has rocketed. It is specified as 25fps, prior to the above changes it would manage around 2 to 5 fps. It now manages 10 to 18fps depending on the picture content.

The IP cam connects to my main OpenWRT router, that is wire connected to a second router, the second router connects via wifi to my laptop, which is what I am viewing the IP cam on. Why should the fps suddenly improve?

[Andy Burns]

You can set a pool of DHCP addresses, whatever is outside the pool is available for static assignment

[Andy Burns]

Might you have previously had a clash of IP addresses?

[John Rumm]

It might be that the router has them allocated to other MAC addresses and the lease has not yet expired.

On networks with lots of devices connecting and disconnecting it can make sense to lower the DHCP lease time to allow addresses allocated to now dormant devices to be re-used sooner.

Have you made sure that you have no fixed IPs set in your DHCP pool?

Typically you want the router to say start allocating DHCP addresses from 192.168.x.100, with a pool of say 100 addresses, then make sure that all static devices are in the 192.168.x.2 - 192.168.x.99 or

192.168.x.201 - 192.168.x.254 range.

It sounds like you had an IP address conflict before.

Sometimes having a quick peak at the PCs ARP table can tell you interesting stuff:

arp -a

You can then lookup the cached mac addresses[1] and see whether they actually correspond to the manufacturer of the device you were expecting (and also whether they stay consistent or flip between macs).

[1] Various web sites like:

For example, taking a snippet from the results on one of my machines I get:

C:\Users\John>arp -a

Interface: 192.168.1.13 --- 0x3 Internet Address Physical Address Type 192.168.1.1 00-1d-aa-71-71-48 dynamic 192.168.1.2 00-50-7f-f1-1a-32 dynamic 192.168.1.4 f4-ec-38-aa-28-a8 dynamic 192.168.1.10 24-5e-be-04-e4-18 dynamic 192.168.1.11 00-18-dd-23-22-3c dynamic 192.168.1.12 38-2c-4a-bc-58-e3 dynamic

(note that the "dynamic" reported here is just indicating that the address has not been specified as static on the PC itself - its not a reflection of if they are actually dynamic addresses on the network)

Which if you look em up shows, Draytek, Draytek, TP-Link, QNAP, Silicon Dust Engineering, ASUSTek Computer Inc

Also has your second router got its DHCP server enabled? You only want one DHCP server active per subnet, or otherwise there is a danger of address conflicts unless you have carefully set them up to allocate addresses from non overlapping pools, and also outside the range used for any static IPs.

[Andy Burns]

Generally, yes you do

Though openWRT can cope with multiple non-authoritative DHCP servers, I've not checked what it does, but probably gratuitous arp on behalf of the address it proposes to lease?

[Harry Bloomfield, Esq.]

Andy Burns wrote on 26/09/2020 :

Thanks, I might give that a go. I hadn't spotted anything in the set up menus..

[Harry Bloomfield, Esq.]

Andy Burns presented the following explanation :

I don't think so, it always ran at the earlier speed, even before I swapped out the router for the OpenWRT one. Before it had a static IP, but in a reserved area of IP's.

[Harry Bloomfield, Esq.]

John Rumm laid this down on his screen :

That makes sense, I did always wonder why the lease time was adjustable.

[Harry Bloomfield, Esq.]

Andy Burns was thinking very hard :

It's a while since I last messed around with my routers and stupidly, at first I tried setting the static addresses on my none OpenWRT router, which is not the DHCP server, yet serve most of the IP's. I was then puzzled as to why the IP's of the items on my LAN remained as before, until it dawned on me.

[Andy Burns]

It's odd that LUCI doesn't expose it (unless there's an add-on module?) you can do it from ssh

[John Rumm]

Worth noting that with much modern kit it may preserve a cache of MAC / IP pairs even after lease expiry, so it can re-issue the same address later where possible (although it can still re-allocate and address if the lease has expired and it has run out of free pool addresses to meet the current demand)

[Chris Green]

Always true in my experience with routers over the past several years, the router always assigns the same IP to a given MAC address unless you explicitly tell it not to.

[Harry Bloomfield, Esq.]

Chris Green has brought this to us :

The problem I was seeing, was with (both his and hers) laptops coming out of hibernation, having no connection to a router and sometimes not even showing my routers in the wifi list. It would show lots of other local ones, just not mine, or if it did would report as being unable to connect to them.

The only way to regain a connection, was to run a cold-boot.

[Dave Plowman (News]

Yes. I have a fairly old BT router. Ages ago, I did a list of what was where - as this ancient machine prefers a fixed IP address. Did the same recently - and was surprised to see the various Wi-Fi devices that aren't on all the time still had the same ones.

It also has the ability to lock a MAC address to an IP one too.

[John Rumm]

That I have found that is quite often a laptop problem where if you sleep and wake it enough times, then the wifi just stops behaving in any sensible way. Sometimes only a power off and back on again (i.e. not just a restart) will fix it.

[Bob Eager]

I use mainly fixed IP addresses - they have infinite leases. I have a small pool of addresses for guests, and they have a lease time of 12 hours.