// O. Bonaventure, 2019 // This script demonstrates the utilisation of Fast retransmit // and RTO with a simplified TCP stack // // enforce strict segment checking (and turn off gso) to measure probe length --strict_segments --ip_version=ipv6 --local_ip=fd::1 --gateway_ip=fd::2 --remote_ip=fd::3 `../common/defaults.sh ip -6 route change fd::3 via fd::2 dev tun0 advmss 1000 mtu lock 1460 initcwnd 16 ethtool -K tun0 gso off tso off ../common/set_sysctls.py /proc/sys/net/ipv4/tcp_timestamps=0 \ /proc/sys/net/ipv4/tcp_syn_retries=3 \ /proc/sys/net/ipv4/tcp_synack_retries=3 \ /proc/sys/net/ipv4/tcp_sack=0 \ /proc/sys/net/ipv4/tcp_dsack=0 \ /proc/sys/net/ipv4/tcp_frto=0 \ /proc/sys/net/ipv4/tcp_reordering=3 \ /proc/sys/net/ipv4/tcp_congestion_control=reno \ /proc/sys/net/ipv4/tcp_slow_start_after_idle=1 \ /proc/sys/net/ipv4/tcp_early_retrans=0 \ /proc/sys/net/ipv4/tcp_recovery=0 \ /proc/sys/net/ipv4/tcp_ecn=0 \ /proc/sys/net/ipv4/tcp_fastopen=0 \ /proc/sys/net/ipv4/tcp_window_scaling=0 \ /proc/sys/net/ipv4/tcp_rmem="64000 64000 64000" \ /proc/sys/net/ipv4/tcp_wmem="64000 64000 64000" \ /proc/sys/net/ipv4/tcp_retries1=3 \ /proc/sys/net/ipv4/tcp_retries2=3 \ ` 0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3 +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0 +0 bind(3, ..., ...) = 0 +0 listen(3, 1) = 0 +.1 < S 0:0(0) win 50000 +0 > S. 0:0(0) ack 1 win 20000 +0 < . 1:1(0) ack 1 win 50000 +.1 accept(3, ..., ...) = 4 // initial congestion window is 16KBytes // server sends 8000 bytes +0 %{ print "retransmissions @1: ",tcpi_bytes_retrans }% +.1 write(4, ..., 8000) = 8000 +0 > . 1:1001(1000) ack 1 +0 > . 1001:2001(1000) ack 1 +0 > . 2001:3001(1000) ack 1 // lost +0 > . 3001:4001(1000) ack 1 // lost +0 > . 4001:5001(1000) ack 1 +0 > . 5001:6001(1000) ack 1 +0 > . 6001:7001(1000) ack 1 +0 > P. 7001:8001(1000) ack 1 // client acks one segments +.1 < . 1:1(0) ack 1001 win 50000 +0 < . 1:1(0) ack 2001 win 50000 +0 < . 1:1(0) ack 2001 win 50000 +0 < . 1:1(0) ack 2001 win 50000 +0 < . 1:1(0) ack 2001 win 50000 // server retransmits after three duplicate acks +0 > . 2001:3001(1000) ack 1 +0 < . 1:1(0) ack 2001 win 50000 +0 < . 1:1(0) ack 2001 win 50000 // client acks retransmission +0 %{ print "retransmissions @2: ",tcpi_bytes_retrans }% // prints 1000 +0 %{ print "RTO @2: ",tcpi_rto }% // prints 224000 +.1 < . 1:1(0) ack 3001 win 50000 +.024 > . 3001:4001(1000) ack 1 // client acks everything +.1 < . 1:1(0) ack 8001 win 50000 +2 < R 1:1(0) ack 8001 win 50000 //`/tmp/sysctl_restore_${PPID}.sh`