$cat /proc/sys/net/ipv4/tcp_mtu_probing 0 $ tcp_mtu_probing – INTEGER Controls TCP Packetization-Layer Path MTU Discovery. Takes three values: 0 – Disabled 1 – Disabled by default, enabled when an ICMP black hole detected 2 – Always enabled, use initial MSS of tcp_base_mss. source : Linux kernel Documentation. 2.6.32 147: /* Black hole detection */ 148: tcp_mtu_probing(icsk, sk); …