pass flag from server to client to script

Simon Hobson dhcp1 at
Wed Jun 13 19:24:15 UTC 2007

Carl Karsten wrote:
>I am trying to figure out how a script can detect if a laptop is on 
>'my' network or somewhere else.
>The plan is to un/mount nfs mounts, flip proxy settings, apt-get 
>upgrade, maybe even sync some data.
>The trick is figuring out when the laptop has transitioned from 'out there' to
>'in here.'
>The hope is to set something in dhcpd.conf like 
>network-id='garblygookUUID' that can be sent to the client that can 
>somehow be tested for in the script.  I am guessing this is outside 
>the dhcp spec, but may be a feature of ics's client.

I believe you can configure the client to ask for arbitrary options, 
and you can certainly configure arbitrary user defined options in the 
ISC server - so that's one route you could use. Would vendor options 
be the best way to deal with this ?

Alternatively, could you look at other properties of your network ? 
Eg Does the MAC address of the router match yours ? Can you resolve a 
fqdn that only exists internal to your network ? Is the domain name 
'internal.<mydomain>.com' ?

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