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Retain DHCP Lease Information after a Reboot

By default, dnsmasq stores DHCP lease data in (volatile) RAM. This means that operations such as a reboot will erase the lease database, forcing a new one to be created. This could be inconvenient, since client devices might receive a new IP address after DHCP renewal. For dnsmasq to maintain its DHCP lease information, the router needs persistent storage, (such as USB).

There are currently two common methods for dealing with this.

Method 1: Store the lease database on permanent storage

The first method does not use scripting. The goal of the first method is to store the lease database on permanent storage.

  1. Under Advanced, go to the DHCP/DNS/TFTP menu. In the Dnsmasq Custom configuration field, enter:


  2. Use a path relative to your own system. Click Save.

  3. Using permanent storage means client devices won't lose connectivity if the router reboots. Because the lease database is not stored in RAM, a reboot won't erase it. This can be useful, for example, when devices are connected to a switch. Moreover, clients won't display in the Device List as having an active lease until their current lease expires, and they've requested a new one. FreshTomato will just continue where if left off.

  4. Notice that the example points to a USB device labelled “usb”. You might have a different name on your system, depending on how storage was formatted. This also means you can store the data on other permanent media, like a CIFS share. However, for such configurations, it is not wise to use JFFS. JFFS is not recommended for frequent writes (which in this case, would occur every time a new IP is sent).

Method 2: Copying the lease database to permanent storage at halt time

The second approach is to keep the lease database in its default location and copy it to permanent storage at “halt” time. It is later restored when the init process runs during boot.

For example, in the Init field in the Scripts menu, enter:

[ -f /mnt/usb/dnsmasq.leases ] && {
sort -b -k 2 -u -z /tmp/var/lib/misc/dnsmasq.leases > /tmp/dnsmasq.tmp1
sort -b -k 2 -u -z /mnt/usb/dnsmasq.leases > /tmp/dnsmasq.tmp2
diff -a /tmp/dnsmasq.tmp1 /tmp/dnsmasq.tmp2 | grep -E '^>' | sed 's/^>\ //' >> /tmp/var/lib/misc/dnsmasq.leases
kill -HUP `ps | grep -E [d]nsmasq | awk '{ print $1 }'`
rm /tmp/dnsmasq.tmp1
rm /tmp/dnsmasq.tmp2
rm -f /mnt/usb/dnsmasq.leases

in the Halt field In the Scripts menu, enter:

cp -f /tmp/var/lib/misc/dnsmasq.leases /mnt/usb/dnsmasq.leases

Method 2 can be used with any type of storage, including JFFS. When using method 2 only with USB, an alternative is to enter the former set of configuration lines into the Run after mounting field and the latter set of lines in the Run before unmounting fields in the USB Support menu.

retain_dhcp_lease_info_after_a_reboot.txt · Last modified: 2023/08/15 18:32 by petervdm