I want to configure a system to listen on an address that it doesn't
actually have until I add the address to the network interface.
It works OK on Raspberry Pi systems but apparently not on a pretty
standard ubuntu Linux system.
When I try to start dnsmasq I get this error:-
root@esprimo# systemctl status dnsmasq.service
× dnsmasq.service - dnsmasq - A lightweight DHCP and caching DNS server
Loaded: loaded (/lib/systemd/system/dnsmasq.service; enabled; vendor
preset: enabled)
Active: failed (Result: exit-code) since Sun 2022-02-13 16:56:27 GMT;
1min 46s ago
Process: 3839 ExecStartPre=/etc/init.d/dnsmasq checkconfig
(code=exited, status=0/SUCCESS)
Process: 3847 ExecStart=/etc/init.d/dnsmasq systemd-exec (code=exited,
status=2)
CPU: 19ms
Feb 13 16:56:27 esprimo systemd[1]: Starting dnsmasq - A lightweight DHCP
and caching DNS server...
Feb 13 16:56:27 esprimo dnsmasq[3847]: dnsmasq: failed to create listening
socket for 192.168.1.2: Cannot assign requested address
Feb 13 16:56:27 esprimo dnsmasq[3847]: failed to create listening socket
for 192.168.1.2: Cannot assign requested address
Feb 13 16:56:27 esprimo dnsmasq[3847]: FAILED to start up
Feb 13 16:56:27 esprimo systemd[1]: dnsmasq.service: Control process
exited, code=exited, status=2/INVALIDARGUMENT
Feb 13 16:56:27 esprimo systemd[1]: dnsmasq.service: Failed with result
'exit-code'.
Feb 13 16:56:27 esprimo systemd[1]: Failed to start dnsmasq - A lightweight
DHCP and caching DNS server.
In the dnsmasq man page it has:-
-z, --bind-interfaces
On systems which support it, dnsmasq binds the wildcard address,
even when it
is listening on only some interfaces. It then discards requests
that it
shouldn't reply to. This has the advantage of working even when
interfaces come
and go and change address. This option forces dnsmasq to really bind
only the
interfaces it is listening on. About the only time when this is
useful is when
running another nameserver (or another instance of dnsmasq) on the
same ma‐
chine. Setting this option also enables multiple instances of
dnsmasq which
provide DHCP service to run in the same machine.
I thought this would mean I could do what I want which is to have:-
listen-address=192.168.1.2,127.0.0.1
... and only actually create the IP 192.168.1.2 on the network interface
when I want this system to be the DHCP/DNS server.
Does the error mean that Ubuntu Linux isn't among "systems which support it"?
Is there any other way to get the result I want? That is dnsmasq running but
not
actually being visible as a server on the LAN until I do something to "switch it
on"?
--
Chris Green
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