mod_xml_radius concurrency limit

[Ričardas Stoma]

I'm using mod_xml_radius module to do radius authentication and accounting.
When doing stress test (using sipp), i noticed that EVERY time when the
number of concurrent calls reached exactly 245, authentications started to
fail.

>From the logs, i see these errors appearing after 245 calls: freeswitch:
rc_send_server: no reply from RADIUS server localhost.localdomain:1812,
127.0.0.1

FreeSwitch and FreeRadius are communicating over localhost. I'm using 3
servers to do this stress test. First server generates calls, seconds
server does freeswitch + freeradius stuff and third servers is used for
terminating calls. Calls are generated with RTP stream.

Wireshark shows that freeradius is sending correct responses to every
mod_xml_radius request, but after 245 calls, responses do not reach
destination (i see error messages "destination port is unreachable").

When the number of concurrent calls drops below 245, new calls are
authenticated correctly (until it reaches that weird 245 limit).

I'm using CentOS 6 (64 bit)

Does anyone know why i'm getting this weird limitation? Is this related to
freeswitch? freeradius server? mod_xml_radius? freeradius-client? linux?
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