[Dnsmasq-discuss] dnsmasq and option 78

[Geert Stappers]

On Mon, Mar 09, 2020 at 01:09:48PM +0100, Kristian Evensen wrote:
> Hello,
> 
> I am trying to configure dnsmasq to export DHCP option 78 (rfc2610) to
> the clients on my network, but I am struggling to make it work. My
> problems seems to be caused by the "Mandatory" byte that has to be
> part of the option.
> 
> My initial attempt was to add the following to dnsmasq.conf:
> dhcp-option-force=78,1,192.168.5.14
> 
> However, this caused dnsmasq to fail with the following error message:
> Mon Mar  9 11:55:55 2020 daemon.crit dnsmasq[3232]: bad IPv4 address
> at line 38 of /etc/dnsmasq.conf
> 
> I then tried to replace "1" with 0x01 and 1b, but in my packet capture
> I see that the values are sent as strings (so "0x01" and "1b"). I then
> tried to just add 1 (so dhcp-option-force=78,1), which worked in the
> sense that dnsmasq did not fail to start and an integer was sent to my
> client.
> 
> Has anyone managed to configure dnsmasq to export option 78 or know
> how to combine an integer with an address list? My router is running
> dnsmasq verson 2.80.

With 2.81rc3 I can reproduce the error and
 dhcp-option-force=78,0x01,192.168.5.14
works ...

<screenshot>
$ sudo systemctl status dnsmasq-virt.service
● dnsmasq-virt.service - dnsmasq virt - DHCP and DNS server
   Loaded: loaded (/etc/systemd/system/dnsmasq-virt.service; enabled; vendor preset: enabled)
   Active: failed (Result: exit-code) since Mon 2020-03-09 21:42:31 CET; 25s ago
  Process: 2998
ExecStart=/home/gs0604/src/mailinglists/dnsmasq/src/dnsmasq --keep-in-foreground --conf-file=/home/gs0604/etc/dnsmasq-virt0.conf
(code=exited, statu Main PID: 2998 (code=exited, status=1/FAILURE)

mrt 09 21:42:31 trancilo systemd[1]: Started dnsmasq virt - DHCP and DNS server.
mrt 09 21:42:31 trancilo dnsmasq[2998]: dnsmasq: bad IPv4 address at line 36 of /home/gs0604/etc/dnsmasq-virt0.conf
mrt 09 21:42:31 trancilo dnsmasq[2998]: bad IPv4 address at line 36 of /home/gs0604/etc/dnsmasq-virt0.conf
mrt 09 21:42:31 trancilo systemd[1]: dnsmasq-virt.service: Main process exited, code=exited, status=1/FAILURE
mrt 09 21:42:31 trancilo dnsmasq[2998]: FAILED to start up
mrt 09 21:42:31 trancilo systemd[1]: dnsmasq-virt.service: Failed with result 'exit-code'.
$ vi ~/etc/dnsmasq-virt0.conf 
$ sudo systemctl restart dnsmasq-virt.service
gs0604 at trancilo:~/src/mailinglists/dnsmasq
$ sudo systemctl status dnsmasq-virt.service
● dnsmasq-virt.service - dnsmasq virt - DHCP and DNS server
   Loaded: loaded (/etc/systemd/system/dnsmasq-virt.service; enabled; vendor preset: enabled)
   Active: active (running) since Mon 2020-03-09 21:44:23 CET; 9s ago Main PID: 3050 (dnsmasq)
    Tasks: 1 (limit: 4915)
   Memory: 340.0K
   CGroup: /system.slice/dnsmasq-virt.service
           └─3050 /home/gs0604/src/mailinglists/dnsmasq/src/dnsmasq --keep-in-foreground --conf-file=/home/gs0604/etc/dnsmasq-virt0.conf

mrt 09 21:44:23 trancilo dnsmasq-tftp[3050]: warning: /srv/tftp inaccessible
mrt 09 21:44:23 trancilo dnsmasq[3050]: reading /etc/resolv.conf
mrt 09 21:44:23 trancilo dnsmasq[3050]: using nameserver 172.24.0.7#53
mrt 09 21:44:23 trancilo dnsmasq[3050]: read /etc/hosts - 73 addresses
mrt 09 21:44:23 trancilo dnsmasq-dhcp[3050]: read /home/gs0604/etc/dnsmasq-virt0-optsfile
mrt 09 21:44:23 trancilo dnsmasq-dhcp[3050]: read /home/gs0604/etc/dnsmasq-virt0-hostsdir/deb10pxe
mrt 09 21:44:23 trancilo dnsmasq-dhcp[3050]: read /home/gs0604/etc/dnsmasq-virt0-hostsdir/db10
mrt 09 21:44:23 trancilo dnsmasq-dhcp[3050]: read /home/gs0604/etc/dnsmasq-virt0-hostsdir/nebo
mrt 09 21:44:23 trancilo dnsmasq-dhcp[3050]: read /home/gs0604/etc/dnsmasq-virt0-hostsdir/vmrtr
mrt 09 21:44:31 trancilo dnsmasq-dhcp[3050]: RTR-ADVERT(ovsbr0) fd45:bd2a:bb0b:1001::
$ grep =78 ~/etc/dnsmasq-virt0.conf 
dhcp-option-force=78,0x01,192.168.5.14
$ 
</screenshot>


Regards
Geert Stappers
-- 
Silence is hard to parse