Linux TCPIP Kernel Parameter Optimization

This document uses the default configuration of ubuntu 12.04 lts desktop (x64) as an example (the memory of the machine is 4 GB). Read this document first.TCP connection status and closing method and their impact on server and client,TCP Parameter Optimization in WindowsTo learn about TCP optimization.

/Proc/sys/NET directory

All TCP/IP parameters are in the/proc/sys/NET directory (note that modifications to the content in the/proc/sys/NET directory are temporary, any modifications will be lost after the system is restarted), such as the following important parameters:

Parameter (Path+File)	Description	Default Value	Optimization Value
/Proc/sys/NET/CORE/rmem_default	The default size of the TCP Data Receiving Window (in bytes ).	229376	256960
/Proc/sys/NET/CORE/rmem_max	Maximum TCP Data Receiving Window (in bytes ).	131071	513920
/Proc/sys/NET/CORE/wmem_default	The default size of the TCP data transmission window (in bytes ).	229376	256960
/Proc/sys/NET/CORE/wmem_max	Maximum TCP data transmission window (in bytes ).	131071	513920
/Proc/sys/NET/CORE/netdev_max_backlog	The maximum number of packets that can be sent to the queue when each network interface receives packets faster than the kernel processes these packets.	1000	2000
/Proc/sys/NET/CORE/somaxconn	Defines the maximum length of the listening queue for each port in the system. This is a global parameter.	128	2048
/Proc/sys/NET/CORE/optmem_max	The maximum buffer size allowed by each socket.	20480	81920
/Proc/sys/NET/IPv4/tcp_mem	Determine how the TCP stack reflects memory usage. The unit of each value is a memory page (usually 4 kb ). The first value is the lower limit of memory usage, the second value is the upper limit of the application pressure on the buffer zone starting from the memory pressure mode, and the third value is the upper limit of memory usage. At this level, messages can be discarded to reduce memory usage. For larger BDP values, you can increase these values (note that the unit is the Memory Page rather than the byte ).	94011 125351 188022	131072 262144 524288
/proc/sys/NET/IPv4/tcp_rmem	defines the memory used by the socket for automatic optimization. The first value is the minimum number of bytes allocated to the socket receiving buffer; the second value is the default value (this value will be overwritten by rmem_default ), the buffer can be increased to this value when the system load is not heavy. The third value is the maximum number of bytes of the received buffer space (this value will be overwritten by rmem_max ).	4096 87380 4011232	8760 256960 4088000
/Proc/sys/NET/IPv4/tcp_wmem	Defines the memory used by the socket for automatic optimization. The first value is the minimum number of bytes allocated for the socket sending buffer; the second value is the default value (this value will be overwritten by wmem_default ), the buffer can be increased to this value when the system load is not heavy. The third value is the maximum number of bytes in the sending buffer space (this value will be overwritten by wmem_max ).	4096 16384 4011232	8760 256960 4088000
/Proc/sys/NET/IPv4/tcp_keepalive_time	The interval (in seconds) between the TCP send keepalive detection message and is used to confirm whether the TCP connection is valid.	7200	1800
/Proc/sys/NET/IPv4/tcp_keepalive_intvl	Interval (in seconds) for resending a message when no response is received ).	75	30
/Proc/sys/NET/IPv4/tcp_keepalive_probes	Maximum number of keepalive probe messages that can be sent before the TCP connection is determined to be invalid.	9	3
/Proc/sys/NET/IPv4/tcp_sack	Enable selective response (1 indicates enabled) to improve performance by selectively responding to messages received in disordered order, so that the sender can send only the lost packet segment (for Wan communication) this option should be enabled, but will increase the CPU usage.	1	1
/Proc/sys/NET/IPv4/tcp_fack	Enable the forwarding response function. You can select a response (sack) to reduce congestion. This option should also be enabled.	1	1
/Proc/sys/NET/IPv4/tcp_timestamps	The TCP timestamp (which will add 12 bytes to the TCP Header) enables RTT calculation in a more precise way (refer to RFC 1323, this option should be enabled for better performance.	1	1
/Proc/sys/NET/IPv4/tcp_window_scaling	Enable the Window Scaling defined in RFC 1323. To support a TCP window larger than 64 KB, you must enable this value (1 indicates enabled). The maximum TCP window size is 1 GB, it takes effect only when both TCP connections are enabled.	1	1
/Proc/sys/NET/IPv4/tcp_syncookies	Indicates whether to enable the TCP synchronization tag (syncookie). The config_syn_cookies must be enabled in the kernel for compilation. The synchronization tag can prevent a socket from overload when too many connections are attempted.	1	1
/Proc/sys/NET/IPv4/tcp_tw_reuse	Indicates whether to allow the time-Wait socket (the port of Time-Wait) to be used for the new TCP connection.	0	1
/Proc/sys/NET/IPv4/tcp_tw_recycle	Time-Wait socket can be recycled more quickly.	0	1
/Proc/sys/NET/IPv4/tcp_fin_timeout	For local-end closed socket connections, TCP stays in the fin-wait-2 State (in seconds ). The other party may disconnect or never end the connection or unexpected process will die.	60	30
/Proc/sys/NET/IPv4/ip_local_port_range	Indicates the local port number allowed by the TCP/UDP protocol	32768 61000	1024 65000
/Proc/sys/NET/IPv4/tcp_max_syn_backlog	For connection requests that have not been confirmed by the other party, the maximum number of connections in the queue can be saved. If the server is overloaded frequently, add this number.	2048	2048
/Proc/sys/NET/IPv4/tcp_low_latency	This option should be disabled to allow TCP/IP stack to adapt to low latency under high throughput.	0
/Proc/sys/NET/IPv4/tcp_westwood	Enable the congestion control on the senderAlgorithmIt can maintain the throughput evaluation and try to optimize the overall utilization of bandwidth. This option should be enabled for Wan communication.	0
/Proc/sys/NET/IPv4/tcp_bic	Enable binary increase congestion for a fast long-distance network so that you can better use the link for operations at the GB speed. This option should be enabled for Wan communication.	1

 

/Etc/sysctl. conf file

/Etc/sysctl. conf is an interface that allows you to change the running Linux system. It includes some advanced options for TCP/IP stack and virtual memory system, which can be used to control Linux network configuration. Due to the temporary content of the/proc/sys/NET directory, we recommend that you add the TCPIP parameter to/etc/sysctl. CONF file, save the file, and use the command "/sbin/sysctl-P" to make it take effect immediately. For specific modification plans, refer to the above:

Net. Core. rmem_default = 256960

Net. Core. rmem_max = 513920

Net. Core. wmem_default = 256960

Net. Core. wmem_max = 513920

Net. Core. netdev_max_backlog = 2000

Net. Core. somaxconn = 2048

Net. Core. optmem_max = 81920

Net. ipv4.tcp _ mem = 131072 262144 524288

Net. ipv4.tcp _ rmem = 8760 256960 4088000

Net. ipv4.tcp _ WMEM = 8760 256960 4088000

Net. ipv4.tcp _ keepalive_time = 1800

Net. ipv4.tcp _ keepalive_intvl = 30

Net. ipv4.tcp _ keepalive_probes = 3

Net. ipv4.tcp _ sack = 1

Net. ipv4.tcp _ fack = 1

Net. ipv4.tcp _ timestamps = 1

Net. ipv4.tcp _ window_scaling = 1

Net. ipv4.tcp _ syncookies = 1

Net. ipv4.tcp _ tw_reuse = 1

Net. ipv4.tcp _ tw_recycle = 1

Net. ipv4.tcp _ fin_timeout = 30

Net. ipv4.ip _ local_port_range = 1024 65000

net. ipv4.tcp _ max_syn_backlog = 2048