Enabling DHCPd listen on dynamically generated interfaces

Shankar shankarbhatm at gmail.com
Tue May 1 17:43:33 UTC 2012

Thanks Simon for your response. Please view inline.

>>1. I've reasonable number (say, 200) of remote clients and if ONE of 
>>them flap, I'll end up automatically reload/restart of dhcp service 
>>on my Debian.
>>Would this impact dhcp services on existing interfaces ?

>Yes, while the server is down, it won't be servicing any requests. 
>However, for most common configs, the restart doesn't take long.

Hmm. I think, that'll be regarded as impact for a production deployment :).

>>2. What is the precise difference between 
>>"/etc/init.d/isc-dhcp-server restart and reload options" ?. Am 
>>inclined for 'reload', but would love to hear from community.

>Have a look at the script - I suspect you'll find they do the same 
>thing. I've just looked at a box I run with 4.1.1 - it doesn't have 
>reload, but it does have force-reload which does nothing different to 
>restart. In any case, the daemon itself does *not* have a reload 

Yes, you are right. Thank You. I meant 'force-reload'.

>>3. Are there any other/ better ways to address above scenarios ?

>Have you considered using a relay agent instead ? That way you can 
>keep the server running. I don't think you'll be able to run one 
>relay agent per client connection because of the need for each one to 
>listen on the connection to the server.

>BTW - what is the interface type that's dynamically generated ? I'm 
>assuming not PPP since I didn't think the ISC server works on those.

They are l2tp tunnels, which gets established and tore down dynamically.
Do we've need 'dhcp relay' when server to remote client is over pure L2 ?.
Reason being, when client send "DHCPDISCOVER", I see them on respective
tunnels @ Debian box.


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