[Dnsmasq-discuss] Is there any way found this "Cannot assign requested address"?

[Chris Green]

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 at 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