DHCP Address Reservation (increase limit beyond 32 please?)

[jbell324]

Hi TPG.

I have had a TP-Link Archer VR1600v and now have a TP-Link VX220-G2v, both supplied by TPG.

I want to use DHCP Address Reservation for more than 32 devices please.  At the moment, there is a limitation of 32 devices, which occurs on both the previous modem/router and the current modem/router.

Is this limtiation imposed by TPG or is it imposed by TP-Link?  Yes, I know that I can use DHCP, and do so, but I want a cluster of PCs that I have to use Address Reservation.

If the limitation is a TPG thing, insofar as 'TPG firmware applied onto the TP-Link device', can you please either a) remove this limitation or b) increase the limit to something much bigger, like 100 devices please?

I have a piece of scientific/academic software, written by others, that seems to suffer/glitch-out when DHCP renews IP leases and I want to eliminate this issue.

regards

Justin

[BasilDV]

Hi @jbell324

We'd like to check on this further.

Kindly send us a private message with your account details.

BasilDV

[david64]

Hi @jbell324 . TPG do modify the firmware of their supplied routers, specifically the VOIP function, and also to remove certain features. So, they could increase the number of reservations (and the number of wifi devices that can connect), but don't expect it any time soon.

You could change the adapter properties on the PCs to use a specific ip address. A bit harder to manage since each PC will be different.

If you are having that many devices, I think it will overwhelm the router with workload.

Strange that the academic software is affected by renewing the ip address.

[jbell324]

Thanks David.

Yes, it was written a while ago, probably 15 years past, and it's not in the language that the main author is familiar with.  I expect it was written in C/C++.  The software I use is scientific number crunching so is all DOS.

Basically, I want to eliminate DHCP on all of the 'Agent' PCs that talk to the 'Manager' PC, hoping this will help resolve a communications failure that seems to trigger randomly with that software.  I suspect it is caused by 'IP Lease Renewal' on the network, but I'm not sure.  It's a process of elimination.

Having a Static IP (on the network adaptor side) and a DHCP Address Reservation for the 'Manager' PC helped reduce the frequency of the software reporting a communications failure.  At that stage, I just had DHCP Address Reservation only and not Static IP.  Once I added both, it reduced the frequency of problems.

I have added other 'Agent' PC, setting Static IPs on each of them, but then ran out of DHCP Address Reservations, hence my request.  I note that I also adjusted the IP Address Pool range, to make sure it is clear of the DHCP Address Reservation.

In terms of traffic, there is not much information sent between the 'Agent' PCs and the 'Manager' PC, it's just some numbers.  There are a lot of devices in the house generally, with children with multiple 'things'.  The last crash of the software though was at 3.29am in the morning, so it was not 'prime time'.

Anyhow, as I understand it, this academic software (it is well beyond my coding capability, and I don't have the source code anyway) may not have a delay in the way that it tries to communicate via TCP/IP.

What I think has happened is that as network speed has increased, from 10/100Mbps, when it was written, to 1000Mbps currently, the software is reacting too fast to any, normally inconsequential, 'hiccip' in the network, incorrectly detects a communications failure and then crashes.

A question, without a spot in DHCP Address Reservation, if I set a Static IP on the network adaptor side, would that PC actually get its requested IP?  I had assumed that I needed either a) both the Static IP and the DHCP Address Reservation or b) just DHCP Address Reservation?

regards

Justin

[david64]

@jbell324 . Are you using switches to connect that many PCs, or are they wifi connections?

The lease time can be set as high as 2880 minutes. After Windows boots up and gets an ip address from router, Windows will try to renew the lease every half-lease-interval. That's usually successful.

Even leaving the dynamic pool as 100 - 199, you could use 200 - 254 as specific addresses to set in the PC network adapters. You could then use the rest for reservations, say 10 - 99.

Once you start using static addresses, you have to manage all static allocations.

I wouldn't expect the use of static adapter addresses to interfere with dynamic allocation or reservations.

As a test, set lease time to 30 minutes. Look at the router system log and note the DHCP messages that come from a PC using dynamic allocation/reservation and from a PC with static address.

While it might look like a DOS program, 15 years ago, WinXP was the go. You could write a Windows program running in a command window using Windows services.

You can check the router system log when you have this crash to see what DHCP activity came from the affected PC. You can use packet capture software (Wireshark) to check for network activity.

While network speeds have increased (10/100 to 1000), so have processor speeds. If it is a real DOS program doing its own timing, that was done by program loops, the loop count calculated for a specific time delay. Faster processor means loop is completing in shorter time; some other expected event may not have happened.

[jbell324]

Thanks David.  You obviously have a lot of experience.  I started with Windows 3.1 myself.

No, the 'Agents' are all connected via ethernet.  I use a star topology to one switch, with distribution from there to one other switch, for each set of 'Agents'.

Thanks for the suggestion re: logging.  I'll look into the VX220-G2v to see what options I have.

In terms of evidence so far, I have output from the academic software and at the time it failed, it lost connection to one 'Agent' and then attempted to reassign that calculation to another 'Agent', and then another, and then another. That attempt at reassignment all took place between 03:29:56.85 and 03:29:56.93.  The sofware then reports a communcations failure and stops working.

Ideally, if I can get the main author to make an attempt, I just need to slow down the rate of checking of connection to these 'Agent' PCs.  If it was a mere 1 second, I think that would be enough.

Anyhow, as per the OP, I am trying to eliminate whatever 'hiccup' initiated that first problem, and have had some success with DHCP Address Reservation and Static IPs, but it could be coincidental.

Secondly, as you've alluded to, it might be that it is 'all too much' for either the TP-Link ArcherVR1600 or this replacement TP-Link VX220-G2V.

regards

Justin