This script can be used to implement persistent leases on openWRT, DD-WRT etc. Persistent leases are good: if the lease database is lost on a reboot, then it will eventually be restored as hosts renew their leases. Until a host renews (which may take hours/days) it will not exist in the DNS if dnsmasq's DDNS function is in use. *WRT systems remount all non-volatile filesystems read-only after boot, so the normal leasefile will not work. They do, however have NV storage, accessed with the nvram command: /usr/lib # nvram usage: nvram [get name] [set name=value] [unset name] [show] The principle is that leases are kept in NV variable with data corresponding to the line in a leasefile: dnsmasq_lease_192.168.1.56=3600 00:41:4a:05:80:74 192.168.1.56 * * By giving dnsmasq the leasefile-ro command, it no longer creates or writes a leasefile; responsibility for maintaining the lease database transfers to the lease change script. At startup, in leasefile-ro mode, dnsmasq will run " init" and read whatever that command spits out, expecting it to be in dnsmasq leasefile format. So the lease change script, given "init" as argv[1] will suck existing leases out of the NVRAM and emit them from stdout in the correct format. The second part of the problem is keeping the NVRAM up-to-date: this is done by the lease-change script which dnsmasq runs when a lease is updated. When it is called with argv[1] as "old", "add", or "del" it updates the relevant nvram entry. So, dnsmasq should be run as : dnsmasq --leasefile-ro --dhcp-script=/path/to/lease_update.sh or the same flags added to /etc/dnsmasq.conf Notes: This needs dnsmasq-2.33 or later to work. This technique will work with, or without, compilation with HAVE_BROKEN_RTC. Compiling with HAVE_BROKEN_RTC is _highly_recommended_ for this application since is avoids problems with the system clock being warped by NTP, and it vastly reduces the number of writes to the NVRAM. With HAVE_BROKEN_RTC, NVRAM is updated only when a lease is created or destroyed; without it, a write occurs every time a lease is renewed. It probably makes sense to restrict the number of active DHCP leases to an appropriate number using dhcp-lease-max. On a new DD_WRT system, there are about 10K bytes free in the NVRAM. Each lease record is about 100 bytes, so restricting the number of leases to 50 will limit use to half that. (The default limit in the distributed source is 150) Any UI script which reads the dnsmasq leasefile will have to be amended, probably by changing it to read the output of `lease_update init` instead. Thanks: To Steve Horbachuk for checks on the script and debugging beyond the call of duty. Simon Kelley Fri Jul 28 11:51:13 BST 2006