Problem - Duplicating IPs

Winfield, Alister Alister.Winfield at
Tue Feb 17 13:56:06 CET 2015

Or find an SNMP MIB in the NAS for the active sessions and check the IP
isn¹t in use before handing it out.

Central IP management is always tricky.. Problem is that the point of
absolute truth (the NAS) isn¹t the point of management (some database
behind RADIUS/DHCP). Avoiding duplicate allocations is hard, even in a
single instance case. Make it multi-server and multi-site and a whole
world of ways to get it wrong are there to trip you up.

Unless you REALLY have to, get the device managing the session (NAS) to
manage the IP allocation, then use Accounting (Start+Interim(s)+Stop) to
track whats in use as required. Yes there are timing delays and small
risks of not having the whole truth due to packet loss. However, the fact
is its much less likely to break the users trying to get connected.


On 16/02/2015 13:44, "Alan DeKok" <aland at> wrote:

>On Feb 16, 2015, at 7:37 AM, Marcelo Santoro < at>
>> I am facing a problem here in my ISP.
>> I have radippool configured in my freeradius 3.0.6 server and some
>>times my customers are receiving Duplicated IP address,
>  Fix your NAS so that it sends the correct accounting packets.
>  FreeRADIUS *assumes* that the accounting information in SQL is correct.
> If the NAS doesn¹t behave properly, the data in SQL will be wrong.  And
>the server will assign duplicate IPs.
>  Until you get a real NAS (or fix your current one), the best solution
>would be to write a script to read IPs from SQL, and then scan those in
>the network.  If there¹s a response, update SQL to mark the IPs as still
>in use.
>  Alan DeKok.
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