[SR-Users] TCP SYN only

Dear all, Since few weeks I have more and more TCP issue, I can see that sometimes the client send a TCP SYN but never get any response. 106.123315 62.12.179.104 -> X.X.X.X TCP 39174 > sip [SYN] Seq=0 Win=4380 Len=0 MSS=1380 TSV=4294942209 TSER=0 WS=1 109.124384 62.12.179.104 -> X.X.X.X TCP 39174 > sip [SYN] Seq=0 Win=4380 Len=0 MSS=1380 TSV=4294942510 TSER=0 WS=1 111.202946 62.12.179.104 -> X.X.X.X TCP 4993 > sip [SYN] Seq=0 Win=4380 Len=0 MSS=1380 TSV=4294942717 TSER=0 WS=1 114.204707 62.12.179.104 -> X.X.X.X TCP 4993 > sip [SYN] Seq=0 Win=4380 Len=0 MSS=1380 TSV=4294943018 TSER=0 WS=1 I have found on internet many doc regarding TCP and max connection issue and I have already done change in sysctl (see below) to increase the number of tcp connection but seems still not ok. Any idea ? Best regards Laurent net.ipv4.ip_forward = 0 net.ipv4.conf.default.rp_filter = 1 net.ipv4.conf.default.accept_source_route = 0 kernel.sysrq = 0 kernel.core_uses_pid = 1 net.ipv4.tcp_syncookies = 0 net.bridge.bridge-nf-call-ip6tables = 0 net.bridge.bridge-nf-call-iptables = 0 net.bridge.bridge-nf-call-arptables = 0 kernel.msgmnb = 65536 kernel.msgmax = 65536 kernel.shmmax = 68719476736 kernel.shmall = 4294967296 net.ipv4.tcp_timestamps = 1 net.ipv4.tcp_fin_timeout = 30 net.ipv4.tcp_keepalive_time = 1200 net.ipv4.tcp_max_syn_backlog = 8192 net.ipv4.tcp_max_tw_buckets = 5000 fs.file-max = 2097152 net.ipv4.ip_local_port_range = 2000 65535 net.ipv4.tcp_max_tw_buckets = 1440000 net.ipv4.tcp_tw_recycle = 1 net.ipv4.tcp_tw_reuse = 1 net.core.somaxconn = 65536 net.core.netdev_max_backlog = 65536