DHCP server control - exclude IPs from range, and clear all leases

I need more control over the DHCP server function of the Max HD2 please.

The ability to exclude IPs from the pool would be really helpful.
I’ve discovered that if a device on the network has a statically assigned IP in the pool the HD2 does not care and will assign it to another device. This causes obvious problems.

It would also be helpful if I could clear the DHCP leases without disabling the DHCP Applying the change and then enabling it and applying the change.

Thanks,
Eric

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Yes this can be a problem with any router. You can work around it by creating pseudo reservations for the static addresses in your Max. To make a reservation you have to enter a MAC address. If you know the MAC of the static device by all means use that but if not just make up one that is unlikely. For example I’ll typically use 00:00:00:00:01, 02, etc. Effectively you’re removing those addresses from the available DHCP range.

Another strategy is to reduce the range of your DHCP assignments so the static devices are not included. The LAN address and subnet of the Max itself can still include the static devices. Only the DHCP range is restricted.

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Don,

Thanks for the feedback. Manually managing this for 70 sites is not ideal. I simply do not have the time for that. The other issue is someone will accidentally assign a device a static IP not realizing it is part of the DHCP scope so I don’t even know it’s an issue until something shows up causing issues and we dig into the troubleshooting to discover what has happened.

The issue at hand is we have blocks of devices with static IPs for various reasons so finding a large enough range as we’re making transitions has been difficult.

Thanks,
Eric

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Agreed this would be helpful sometimes, but since their is nothing in the protocol to get the end host to release the IP we should add help text along the lines of ‘if you clear a DHCP lease there is a risk that there still might be a device that has that IP on the network’.

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Agreed Martin,

However I would assume the Peplink would check the IP before handing it out and if it found a device it would mark that as bad or in use in the DHCP lease table preventing any conflicts after clearing the leases.

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In my experience the Peplink routers will not issue a DHCP address that is already in use by a static device at the time. The problem is static coded devices that may be powered off. The router issues the address because it is not seen on the network at the time. Then at a later time someone turns on the offending device and bad things happpen!

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@eglass

@Don_Ferrario is right that ARP request will be sent to make sure the IP is not in used by any devices in the LAN before the IP is released to the device and this will make sure IP conflict will not happen. The main concerns as Don mentioned will be the common case that the Static IP PC maybe offline/sleep in the network and this cause the IP conflict happen when the Static IP device is online again.

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Hello @eglass,
We have a technique of excluding IPs from the DHCP pool on Peplink/Pepwave devices.
What we do is add in the IPs as a DHCP reservation with MAC addresses starting with 00:00:00:00:00 as seen below.

At the time of writing this, I’ve not worked out a way to do this from InControl2. This solution is at the device level of the DHCP settings.

We had a situation where a client used the same subnet at multiple sites and equipment gets moved between those sites with static IPs, so we came up with this to help them make it work.
Happy to Help,
Marcus :slight_smile:

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