[Dnsmasq-discuss] Possible Bug: DHCPV6 Does Not Make Lease Entry for DHCP CONFIRM

Eric Luehrsen ericluehrsen at hotmail.com
Sun Oct 18 06:09:43 BST 2015


In using the latest OpenWRT 15.05 (C.C.) with DNSMASQ 2.73 is logging DHCP (v6) CONFIRM events with host names but not re-entering them into the lease file. (note, I also saw this late in 14.07 (B.B.) with DNSMASQ for that release so its not new.)

A way to catch this behavior is use (client) a Debian flavor with Network-Manager driving the connections. The sever again OpenWRT with ODHCP removed and just DNSMASQ for all DNS/DHCP services 4/6. Upon its initial connection the client will make a DHCP (v6) SOLICIT. At this time, DNSMASQ will write a lease file entry just as one would expect like DHCP (v4). Then cause the router to reset. Upon reconnecting, the client will issue a DHCP CONFIRM: "just checking this is still mine," DNSMASQ logs the event in syslog, the host name is in syslog, but the host name is not in the lease file.

The lease file information appears to be used by DNSMASQ internally to prevent hashing into the same address for two clients. While unlikely with the advisable DHCP "constructor" of ::1000-::FFFF, this could result in conflicts if DNSMASQ receives multiple SIGUP's from other processes and no lease is found to prevent conflict. The lease files can also be used in third party scripts to establish host identification and provide access to semi-controlled resources. Such as, hotel or restaurant Internet using an authorized "receipt code" check with an on-router intercept website for gating to the world.

-Reboot Router
-Sun Oct 18 00:35:07 2015 daemon.info dnsmasq-dhcp[1811]: DHCPCONFIRM(br-lan) DUID
-Sun Oct 18 00:35:07 2015 daemon.info dnsmasq-dhcp[1811]: DHCPREPLY(br-lan) fdc0:a828::XXXX DUID HOSTNAME
-Sun Oct 18 00:35:07 2015 daemon.info dnsmasq-dhcp[1811]: DHCPREPLY(br-lan) 2001:470:YYYY:YYYY::XXXX DUID HOSTNAME
-No dhcpv6 lease file entry

(Note: It appears when Windows drops/looses a connection for more than a second-ish, it will always SOLICIT and get entered into the lease file.)


ERIC 		 	   		  
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