DHCP module and external DHCP relay

[Eugene Grosbein]

On 04.04.2014 22:44, Alan DeKok wrote:
>   Let me go further...
> 
>   My guess is that you're using MySQL to store IPs.  You're using a
> "SELECT FOR UPDATE ... LIMIT 1" query to grab the IP.
> 
>   That's the problem.  MySQL will lock all of the rows SELECTed, even if
> you say LIMIT 1.  The result is massive lock contention, and MySQL will
> take many seconds to respond.
> 
>   Use a real database, like PostgreSQL. The problem will go away.

We do not use MySQL or SELECT FOR UPDATE.
We use MS SQL and stored procedures there and when hundreds
of simultaneous requests come from _distinct_ MAC addresses without
using DHCP relays, then FreeRADIUS processes them instantly.

But when DHCP relay stays in front of FreeRADIUS, request drops
and bad queueing happen due to wrong assumptions in its code
that looks for duplicates in the queue of requests. These assumptions
are just fine for RADIUS protocol and they are fine for DHCP without relays
but they are plain wrong when all DHCP requests come from single MAC address
of DHCP relay.