IP churn, maybe due to shared-network?

John Wobus jw354 at cornell.edu
Fri Nov 2 15:13:55 UTC 2012

With a bit of scripting to decode your lease file you can
see what state the leases are at a given moment and
get a handle on what is going.

A very quick look online shows a somewhat-aged program at  
DHCPStatus.  I expect there are others.

(It would be cool if dhcpd had an option to do this, something like
-T and -t but verbose about current lease and pool states.)

John Wobus

On Oct 31, 2012, at 9:18 AM, Norman Elton wrote:

> We've noticed that there is a higher-than-expected amount of IP  
> churn for our wireless clients. That is, clients are connecting to  
> the same network, but being assigned different IP addresses in the  
> pool.
> I don't believe it's due to over-subscription. In the past few  
> months, we've had a total of 13K unique devices with 12K available  
> IP addresses. This might affect a transient device or two, but our  
> long-term customers should retain the same IP.
> We do; however, have shared-networks setup. Each shared-network  
> consists of a /21 (2000 clients) and a /23 (500 clients).
> So here's the question ... when there are two subnets defined inside  
> a shared-network, does dhcpd always prefer using A, even if the  
> client has an existing lease from B? That is, does it only use B if  
> A is completely filled with active clients? This would certainly  
> explain the behavior we're observing.
> Thanks!
> Norman Elton
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