IP churn, maybe due to shared-network?

Norman Elton normelton at gmail.com
Wed Oct 31 13:18:50 UTC 2012

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


Norman Elton
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