Hello guys, Finally i found what was my problem. It was about ARP table size, becuase is set to 1024 record in ubuntu. when i try to register a lot of users with different source ip to kamailio (or other sip server like asterisk and etc), after some minutes, the arp table is fulled and these warrning may be issue: In kamailio: Jun 14 16:06:50 172-1-1-158 /usr/local/kamailio-5.0/sbin/kamailio[31864]: ERROR: <core> [core/tcp_read.c:1319]: tcp_read_req(): ERROR: tcp_read_req: error reading - c: 0x7f2518774590 r: 0x7f2518774610 Jun 14 16:06:50 172-1-1-158 /usr/local/kamailio-5.0/sbin/kamailio[31859]: ERROR: <core> [core/tcp_read.c:1319]: tcp_read_req(): ERROR: tcp_read_req: error reading - c: 0x7f2518d4ebf0 r: 0x7f2518d4ec70 Jun 14 16:06:50 172-1-1-158 /usr/local/kamailio-5.0/sbin/kamailio[31868]: ERROR: <core> [core/tcp_read.c:291]: tcp_read_data(): error reading: Connection reset by peer (104) ([192.168.13.227]:59948 -> Jun 14 16:06:50 172-1-1-158 /usr/local/kamailio-5.0/sbin/kamailio[31868]: ERROR: <core> [core/tcp_read.c:292]: tcp_read_data(): -> [192.168.0.221]:5060) Jun 14 16:06:50 172-1-1-158 /usr/local/kamailio-5.0/sbin/kamailio[31868]: ERROR: <core> [core/tcp_read.c:1319]: tcp_read_req(): ERROR: tcp_read_req: error reading - c: 0x7f25191387c0 r: 0x7f2519138840 J In Asterisk: Jun 16 00:59:09 asterisk11 kernel: [ 5042.988477] Neighbour table overflow [Jun 16 00:59:14] WARNING[2811] chan_sip.c: sip_xmit of 0x7f94fd08a4e0 (len 488) to 192.168.14.116:5060 returned -1: No buffer space available you should add some parameters in sysctl.conf in ubuntu: net.ipv4.neigh.default.gc_thresh1 = 512 net.ipv4.neigh.default.gc_thresh2 = 1024 net.ipv4.neigh.default.gc_thresh3 = 2048

Good luck With regards.Mojtaba Esfandiari.S