June 2010 – TRUEANGLE

About RTO retransmission and tcp_orphan_retries

About RTO retransmission and tcp_orphan_retries tcp_orphan_retries – INTEGER This value influences the timeout of a locally closed TCP connection,when RTO retransmissions remain unacknowledged. source : Linux Kernel Documentation . 2.6.32 TYPICAL SHELL ON PROC FILESYSTEM [bash] $cat /proc/sys/net/ipv4/tcp_orphan_retries 0 $ [/bash] TYPICAL SOURCE CODE RELATED [c] net/ipv4/tcp_timer.c – 39 identical 99: static int tcp_orphan_retries(struct sock …

Continue reading “About RTO retransmission and tcp_orphan_retries”

when RTO retransmissions remain unacknowledged…

$cat /proc/sys/net/ipv4/tcp_orphan_retries 0 $ tcp_orphan_retries – INTEGER This value influences the timeout of a locally closed TCP connection, when RTO retransmissions remain unacknowledged. See tcp_retries2 for more details. The default value is 7 If your machine is a loaded WEB server, you should think about lowering this value, such sockets may consume significant resources. Cf. …

Continue reading “when RTO retransmissions remain unacknowledged…”

characteristics about the last connection…

$cat /proc/sys/net/ipv4/tcp_no_metrics_save 0 $ tcp_no_metrics_save Normally, TCP will remember some characteristics about the last connection in the flow cache. If tcp_no_metrics_save is set, then it doesn’t. Useful for benchmarks or other tests. net/ipv4/sysctl_net_ipv4.c – 24 identical 452: { 453: .procname = “tcp_no_metrics_save”, 454: .data = &sysctl_tcp_nometrics_save, github.com/github/linux-2.6.git – GPL – C – More from linux-2.6.git …

Continue reading “characteristics about the last connection…”

controls tcp packetization-layer ..

$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); …

Continue reading “controls tcp packetization-layer ..”

tcp moderate …receive buffer auto-tuning

$cat /proc/sys/net/ipv4/tcp_moderate_rcvbuf 1 $ tcp_moderate_rcvbuf – BOOLEAN If set, TCP performs receive buffer auto-tuning, attempting to automatically size the buffer (no greater than tcp_rmem[2]) to match the size required by the path for full throughput. Enabled by default. source : Linux kernel Documentation kernel ( 2.6.32 ) trunk/coverage/common/ServerSpecs.pm – 1 identical 278: 247 tcp_max_syn_backlog 1024 …

Continue reading “tcp moderate …receive buffer auto-tuning”

tcp mem vector of 3 integers

$cat /proc/sys/net/ipv4/tcp_mem 40704 54272 81408 $ tcp_mem vector of 3 INTEGERs: min, pressure, max min: below this number of pages TCP is not bothered about its memory appetite. pressure: when amount of memory allocated by TCP exceeds this number of pages, TCP moderates its memory consumption and enters memory pressure mode, which is exited when …

Continue reading “tcp mem vector of 3 integers”

timewait sockets held…tw_bucket

$cat /proc/sys/net/ipv4/tcp_max_tw_buckets 180000 $ tcp_max_tw_buckets Maximal number of timewait sockets held by system simultaneously. If this number is exceeded time-wait socket is immediately destroyed and warning is printed. This limit exists only to prevent simple DoS attacks, you _must_ not lower the limit artificially, but rather increase it (probably, after increasing installed memory), if network …

Continue reading “timewait sockets held…tw_bucket”

grep .. -m .. stop reading a file…

-m Stop reading a file after NUM matching lines. $grep -m 1 wc wcwidth.c #include $grep -m 2 wc wcwidth.c #include wchar_t cr; $grep -m 3 wc wcwidth.c #include wchar_t cr; value=wcwidth(cr); $grep -m 4 wc wcwidth.c #include wchar_t cr; value=wcwidth(cr); $grep -m 0 wc wcwidth.c $ scripts/makelst – 338 identical 19: t1=`$3 –syms $1 …

Continue reading “grep .. -m .. stop reading a file…”

remembered connection requests .. syn .. backlog

$cat /proc/sys/net/ipv4/tcp_max_syn_backlog 1024 $ Maximal number of remembered connection requests, which still did not receive an acknowledgement from connecting client. The default value is 1024 for systems with more than 128 MB of memory, and 128 for low memory machines. If server suffers of overload, try to increase this number. source : http://www.linuxinsight.com/proc_sys_net_ipv4_tcp_max_syn_backlog.html Script.January/HPUX11/GEN003600 – …

Continue reading “remembered connection requests .. syn .. backlog”

grep … matches..and that not matches..-l.. -L

$grep -r -l tcp_max * sysctl_net_ipv4.c tcp.c tcp_cong.c tcp_input.c tcp_output.c $ $grep -r -L tcp_max * af_inet.c ah4.c arp.c cipso_ipv4.c datagram.c devinet.c esp4.c fib_frontend.c fib_hash.c fib_lookup.h fib_rules.c fib_semantics.c fib_trie.c icmp.c igmp.c inet_connection_sock.c inet_diag.c inet_fragment.c inet_hashtables.c inet_lro.c inetpeer.c inet_timewait_sock.c ipcomp.c ipconfig.c ip_forward.c ip_fragment.c ip_gre.c ip_input.c ipip.c ipmr.c ip_options.c ip_output.c ip_sockglue.c Kconfig Makefile netfilter/ipt_ECN.c netfilter/nf_nat_amanda.c netfilter/nf_conntrack_l3proto_ipv4.c netfilter/nf_nat_proto_dccp.c …

Continue reading “grep … matches..and that not matches..-l.. -L”