Using Nas IP Adress as client "key"

Johan Meiring jmeiring at
Thu Apr 22 22:36:47 CEST 2010

Hi all,

The radius spec currently identifies a Nas (client) by the Nas's IP address
(Packet-Src-Ip-Addres?).  That is how radius works.

We have a bunch of hotspots out in the field which could be behind any kind
of internet connection.  Broadband/Dynamic IP, natted, etc.

Because we have no idea where a spesific Nas's traffic might come from we've
implemented dynamic-clients.  Using rlm_raw we use the Nas-Identifier to 
lookup the shared secret in a database, and the client gets dynamically 
created.  (Thanks Alan for the help with this one!!)

This works very well, but has a few irritating (not showstopping) side effects.

1)  Sometimes we have more than one Nas behind the same natted connection.
     This means that they all have to have the same shared secret.

2)  Also it happens that a different Nas ends up behind a previous Nas's
     IP (dynamically assigned broadband IP) and then the shared secret
     is again rejected.

Within a corporate/large telco's network, the Nas's (802.11x switches or 
Dslams) are generally behind fixed IPs,  but for the hotspot world any Nas 
source IP goes.

Is it not a maybe a good idea to start considering a different "key" to 
identify the Nas by.

In clients.conf (or for dynamic clients) a paramter ("nas-key") that could 
be Src-IP or Nas-Id.  i.e. you can choose the "key" that identifies a 
spesific Nas/client and therefore the shared secret.

Does it sound like a bad idea?

How difficult would such a change in Freeradius be?
(I've not read the source code yet, just throwing an idea out there).


PS:  I realise that tunneling the radius traffic is a different solution to 
the same problem, but in our case not always easy to implement.  (The only 
extra "layer" I would love to see is RadSec.)


Johan Meiring
Cape PC Services CC
Tel: (021) 883-8271
Fax: (021) 886-7782

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