[SR-Users] Strange issue in registering users in Kamailio

Hello, In now days i have a strange issue in registering users in kamailio. My senario is the following: I setup kamailio with basic configurations and i created 2000 users in mysql(from 10000 to12000). With registration senario with SIPP tool, i have not issue and every things works right,(Notice that we know SIPP uses the same source ip for all registration), But when i use Spirent Abacus 5000(Test solution for voice, VoLTE and IMS), the kamailio just register 1024 users and other users could not register to kamailio. Spirent Abacus 5000 use the different source ip for each registration. I have these error in syslog message: ERROR: sl [../../core/forward.h:201]: msg_send buffer(): udp_send failed one possible reason is the server is bound to localhost I set this parameter in kamailio configurations, but the issue dont solved: open_files_limits:2048 and in linux configuration: ulimit -n 999999 Please let me know how can i fixed it? With Regards. --Mojtaba Esfandiari.S