rlm_sqlippool allocating duplicate IPs

[Phil Mayers]

Phil Mayers wrote:
> Phil Mayers wrote:
>> All,
>>
>> I've just become aware of a rather annoying problem with our PPTP VPN 
>> server. Sometimes, a client will connect, disconnect and reconnect in 
>> quick succession. In these circumstances, there seems to be a window 
>> which an IP can remain allocated to a live VPN session, but is marked as 
>> free in the SQL table, causing subsequent clients to connect, be 
>> allocated the IP, and fail to get any connectivity.
> 
> ACK!
> 
> Shortly after sending this email, we found the problem and it's truly 
> vile. It's nothing to do with FreeRadius at all, except tangentially - 
> what's actually happening is that the PPTP client is closing the PPP LCP 
> layer and re-opening it on the same PPTP control/data channel.
> 
> This results in a very rapid set of:

Ugh. Even worse, it doesn't actually re-authenticate the user; it 
actually just tears down the IPCP layer, and then brings it back up 
again USING THE SAME IP. Of course, since the "stop-clear" query has run 
at that point and re-set the pool_key column to "0", so the 2nd 
accounting start doesn't re-allocate the IP.

That is, it does:

access-request
   allocate-ip
     update pool set nas=%{NAS},pool_key=${pool-key} where ip=%I

accounting-start
     update pool set expires=now()+x where nas=%{NAS} and 
pool_key=${pool-key}

accounting-stop
     update pool set expires=now()-1,pool_key=0 where nas=%{NAS} and 
pool_key=${pool-key}

accounting-start
     update pool set expires=now()+x where nas=%{NAS} and 
pool_key=${pool-key}
     FAILS because pool_key=0 now

Bah. Bah bah bah.