dhclient: lease renewal woes

Simon Hobson dhcp1 at thehobsons.co.uk
Wed Aug 29 12:26:57 UTC 2012

Mr Dash Four wrote:
>I have a bit of a conundrum which is causing me a few problems and I 
>am hoping that any of you might be able to help me with: I am using 
>dhclient to get a lease from my provider via a cable modem. When I 
>acquire a new lease the following sequence occurs:
>1. dhclient broadcasts DHCPREQUEST on;
>2. my cable modem (which has a private IP address) responds and 
>offers a lease;
>3. dhclient then accepts the lease and records it in the .leases file.
>So far so good, but the .leases file has "option 
>dhcp-server-identifier" which points to an external dhcp server 
>(with public IP address in it, say 82.x.x.x). When a time comes and 
>dhclient needs to renew the lease it tries to contact this 82.x.x.x 
>address. The problem with this approach is that my provider's DHCP 
>server doesn't respond to direct queries and they get ignored.

Correct approach - contact your provider and get them to fix their 
broken network.

>As it stands though, when the lease renewal comes about, my dhclient 
>becomes "stuck" and I have to restart it.

What *should* happen is that as the lease expiry time is looming, the 
client should try contacting the server directly a few times. If that 
fails, then shortly before the lease expires, it should try 
broadcasting the request - at which point you should get your answer.
If the lease actually expires then the client should unconfigure the 
interface and then start broadcasting Discovers until it gets a new 

Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
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