Using DHCP for Radius on a Cable Modem Plant

[Alan DeKok]

On Aug 21, 2015, at 3:40 PM, Arran Cudbard-Bell <a.cudbardb at freeradius.org> wrote:
> I'd be interested to know if ISC have found a way to do sparse allocation of DHCP leases.

  Nope.  I had patches for ISC to do that 10 years ago.  They told me it wasn't possible, so they didn't want to see the patches.

> AFAICT our SQL schemas require rows to be inserted into the SQL db, representing each lease in the pool, before the module can allocate them.
> 
> Which is fine, I guess, just seems a little wasteful.

  My patches for ISC tracked ranges: start, stop, last IP checked.  If it couldn't find a lease in the IP table, it looked in the range table, and updated the "last IP checked".  It was pretty simple, TBH.

> The problem with using LDAP for IP allocation, is with OpenLDAP at least, the whole server is setup for read performance.  When you start writing you blow out the object caches in BDB and OpenLDAP and read performance starts to suck too.
> 
> With LMDB you're looking at around 3000 writes/s max, as there's only a single writer thread.
> 
> It's really not designed for balanced read/write loads.  For that you'd want to look at either SQL or one of the numerous in memory K/V stores which have popped up in recent years.

  Yup.  LDAP is fine for static leases.  Dynamic... not so much.

  Alan DeKok.