DGND3700v1 DHCP Lease Time?

[w3wilkes]

I need to extend the default DHCP lease time in my DGND3700v1. This is due to a network error when doing a Bare Metal Restore from a WHS 2011 server to a client PC on the network. It appears that the lease time in the router is 1 hour. This is not sufficient time for the restore to complete and the restore fails on an "unknown network error" after 1 hour. I've searched high and low and cannot find the setting to change the DHCP lease time on the DGND3700v1.

To complete the restore I'm using an old Zoom router with the lease time set to 1 day and the restore runs to completion.

If I cannot modify the DHCP lease time is there another way around this problem on the DGND3700v1? One thought would be to use reserved TCP/IP addresses outside the DHCP range of addresses. Does anyone know if this approach would get around the current DHCP lease time expiring after one hour?

[Babylon5 · Accepted solution]

This is an extract from an archived thread, posted by ‘jlewter’ about five years ago. I’m not sure if the change is persistent through a router power cycle / reboot, and I’m not entirely sure if it can be applied to all routers (in the case below it was a WNDR3700).

"do at your own risk.

telnetenable
log into router
# cd bin
# config backup /tmp/configbackup.bin
(use a usb stick to copy it off)
# config set lan_lease=604800
(this is 7 days, 60*60*24*7 in seconds)
# config commit

Notes here..
*Tinkering with these values are done at your own risk.
*Rebooting will NOT reset this value.
*Editing the LAN / DHCP page in the router will NOT reset this value.
*If you have a lot of different devices coming on and going off then this could slow the router down.
*If you ever change your lease time DOWNWARDS then you need to reboot ALL devices on the network because the lease will EXPIRE on DHCP server and not the client.
*3 - 7 days is the ideal lease time. Setting it for a few mins will be deadly to the router ;P. Setting it for 3 years (nearly) will just be silly.
*Tinkering with these values are done at your own risk.

Side Notes here..
*Settings are exported as plain text (this might be useful for other things)..
*If you dont know how to copy files from the prompt then the command is "cp" and the usb drives are usually mounted under mnt1 or mnt/mnt1 (not gonna check it's late)
*Dont try to enable local DNS caching by changing the values, I did, It still doesnt work..
*Tinkdering with these values are done at your own risk. "

[Babylon5 · Accepted solution]

This is an extract from an archived thread, posted by ‘jlewter’ about five years ago. I’m not sure if the change is persistent through a router power cycle / reboot, and I’m not entirely sure if it can be applied to all routers (in the case below it was a WNDR3700).

"do at your own risk.

telnetenable
log into router
# cd bin
# config backup /tmp/configbackup.bin
(use a usb stick to copy it off)
# config set lan_lease=604800
(this is 7 days, 60*60*24*7 in seconds)
# config commit

Notes here..
*Tinkering with these values are done at your own risk.
*Rebooting will NOT reset this value.
*Editing the LAN / DHCP page in the router will NOT reset this value.
*If you have a lot of different devices coming on and going off then this could slow the router down.
*If you ever change your lease time DOWNWARDS then you need to reboot ALL devices on the network because the lease will EXPIRE on DHCP server and not the client.
*3 - 7 days is the ideal lease time. Setting it for a few mins will be deadly to the router ;P. Setting it for 3 years (nearly) will just be silly.
*Tinkering with these values are done at your own risk.

Side Notes here..
*Settings are exported as plain text (this might be useful for other things)..
*If you dont know how to copy files from the prompt then the command is "cp" and the usb drives are usually mounted under mnt1 or mnt/mnt1 (not gonna check it's late)
*Dont try to enable local DNS caching by changing the values, I did, It still doesnt work..
*Tinkdering with these values are done at your own risk. "

[w3wilkes]

Thank you!

[w3wilkes]

A possible easier alternative than telneting and modifying the firmware config??

I’m guessing that a reserved IP address in the router (Advanced -> LAN Setup -> Address Reservation) outside the DHCP address range would not have to deal with lease renewal? I’m guessing that with a reserved IP address outside the DHCP range that the DHCP code would not establish or release a lease for an IP outside of the DHCP range of managed addresses?

[Babylon5]

That would be like only part of the DHCP process working as designed. If a client requests IP data by DHCP then I would expect it to require a lease time, and on the router side I can’t see why it would respond to a DHCP request by providing an IP address – but without a lease period?

It should be very easy and quick to test your theory of course.

[w3wilkes]

Since I run different firmware than Netgears I was able to edit dnsmasq.conf and change the lease time for the device I needed to on. This should still be considered a major shortcoming in the Netgear firmware. If the lease time is going to be hardcoded in the firmware without the ability to change it, the default should be at least 12 hours! The default of 1 hour is not only insufficient in some circumstances (like doing a Bare Metal Restore to a WHS2011 client), but needlessly increases overhead on the router which negatively impacts the router's performance.

[Babylon5]

Don’t forget that clients attempt to renew leases at the half time period, so a lease time of 12 hours means that renewal will first be attempted at six hours, the second will be at 87.5% of 12 hours, and the client will unbind the lease at the expiry time.

One hour leases mean renewals at 30 minute periods.

[w3wilkes]

With the default of 1 hour DHCP leases and my 15 DHCP managed devices my router is doing quite a bit of overhead doing nothing but lease management. Kinda makes one wish that the dual core DGND3700 did SMP. I believe that the OS in the router is not configured to take advantage of the dual core processor. I figure if I change the lease times for all DHCP managed connections to 12 hours (dynamic and reserved IP's), I'll save over 90% of the current overhead of lease management in the router.

[Babylon5]

Lease management should not use much bandwidth at all, even with 15 devices leased at 1 hour that would only be about 30-60 packets per hour.

I would however not want such a short lease time from a DHCP server, a much longer time e.g. 1 day would allow me to shut down the gateway for several hours if necessary without disrupting the rest of the network, I have several switches and the gateway has just a single connection to the first switch. In fact when I retired my old Buffalo router and installed the current Draytek, I was able to simply switch over and let the Draytek discover what was on the LAN, and then set all the IP reservations and port forwarding rules without interfering with any LAN devices.

A lease time of 1 hour would mean that all DHCP devices would lose their IP within 30 minutes to 1 hour.

I could propose a firmware enhancement to Netgear if you like?

[w3wilkes]

Andy, Thanks! I believe the one hour lease time is really too short. A lease time of 1 day (86,400) seems like it would be much more appropriate than the current 1 hour that is hard coded in the router. You might also suggest that lease times be user settable. This would give great flexibility to the user to address specific network requirements. If that's out of the question, having the local LAN lease time set to 1 day would be great. Thanks again, Wilkes