How do I set advanced security options of the TCP/IP stack and virtual memory to improve security and performance of my system? How do I configure Linux kernel to prevent certain kinds of attacks using /etc/sysctl.conf? How do I set Linux kernel parameters?

怎样设置 TCP/IP 堆栈和虚拟内存的高级的安全选项,以提高我的系统的安全性和性能?如何配置以防止某些类型的攻击,使用 /etc/sysctl.conf 的 Linux 内核?如何设置 Linux 内核参数?

sysctl is an interface that allows you to make changes to a running Linux kernel. With /etc/sysctl.conf you can configure various Linux networking and system settings such as:

Limit network-transmitted configuration for IPv4
Limit network-transmitted configuration for IPv6
Turn on execshield protection
Prevent against the common ‘syn flood attack’
Turn on source IP address verification
Prevents a cracker from using a spoofing attack against the IP address of the server.
Logs several types of suspicious packets, such as spoofed packets, source-routed packets, and redirects.

sysctl 是允许您更改运行的 Linux 内核的一个借口。通过 /etc/sysctl.conf,您可以配置各种 Linux 网络和系统设置,如:

  1. 限制 IPv4 的网络传输配置
  2. 限制 IPv6 的网络传输配置
  3. 打开 execshield 保护
  4. 防止常见 syn 洪水攻击
  5. 打开源 IP 地址验证
  6. 可以防止骇客使用服务器的 IP 地址欺骗攻击。
  7. 记录几种类型的可疑的数据包,如伪造的数据包,源路由的数据包和重定向。

sysctl command

The sysctl command is used to modify kernel parameters at runtime. /etc/sysctl.conf is a text file containing sysctl values to be read in and set by sysct at boot time. To view current values, enter:
# sysctl -a
# sysctl -A
# sysctl mib
# sysctl net.ipv4.conf.all.rp_filter

 

To load settings, enter:
# sysctl -p
Sample /etc/sysctl.conf

Edit /etc/sysctl.conf and update it as follows. The file is documented with comments. However, I recommend reading the official Linux kernel sysctl tuning help file (see below):

# The following is suitable for dedicated web server, mail, ftp server etc.
# —————————————
# BOOLEAN Values:
# a) 0 (zero) – disabled / no / false
# b) Non zero – enabled / yes / true
# ————————————–
# Controls IP packet forwarding
net.ipv4.ip_forward = 0

# Controls source route verification
net.ipv4.conf.default.rp_filter = 1

# Do not accept source routing
net.ipv4.conf.default.accept_source_route = 0

# Controls the System Request debugging functionality of the kernel
kernel.sysrq = 0

# Controls whether core dumps will append the PID to the core filename
# Useful for debugging multi-threaded applications
kernel.core_uses_pid = 1

# Controls the use of TCP syncookies
#net.ipv4.tcp_syncookies = 1
net.ipv4.tcp_synack_retries = 2

########## IPv4 networking start ##############
# Send redirects, if router, but this is just server
net.ipv4.conf.all.send_redirects = 0
net.ipv4.conf.default.send_redirects = 0

# Accept packets with SRR option? No
net.ipv4.conf.all.accept_source_route = 0

# Accept Redirects? No, this is not router
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.all.secure_redirects = 0

# Log packets with impossible addresses to kernel log? yes
net.ipv4.conf.all.log_martians = 1
net.ipv4.conf.default.accept_source_route = 0
net.ipv4.conf.default.accept_redirects = 0
net.ipv4.conf.default.secure_redirects = 0

# Ignore all ICMP ECHO and TIMESTAMP requests sent to it via broadcast/multicast
net.ipv4.icmp_echo_ignore_broadcasts = 1

# Prevent against the common ‘syn flood attack’
net.ipv4.tcp_syncookies = 1

# Enable source validation by reversed path, as specified in RFC1812
net.ipv4.conf.all.rp_filter = 1
net.ipv4.conf.default.rp_filter = 1

########## IPv6 networking start ##############
# Number of Router Solicitations to send until assuming no routers are present.
# This is host and not router
net.ipv6.conf.default.router_solicitations = 0

# Accept Router Preference in RA?
net.ipv6.conf.default.accept_ra_rtr_pref = 0

# Learn Prefix Information in Router Advertisement
net.ipv6.conf.default.accept_ra_pinfo = 0

# Setting controls whether the system will accept Hop Limit settings from a router advertisement
net.ipv6.conf.default.accept_ra_defrtr = 0

#router advertisements can cause the system to assign a global unicast address to an interface
net.ipv6.conf.default.autoconf = 0

#how many neighbor solicitations to send out per address?
net.ipv6.conf.default.dad_transmits = 0

# How many global unicast IPv6 addresses can be assigned to each interface?
net.ipv6.conf.default.max_addresses = 1

########## IPv6 networking ends ##############

#Enable ExecShield protection
kernel.exec-shield = 1
kernel.randomize_va_space = 1

# TCP and memory optimization
# increase TCP max buffer size setable using setsockopt()
#net.ipv4.tcp_rmem = 4096 87380 8388608
#net.ipv4.tcp_wmem = 4096 87380 8388608

# increase Linux auto tuning TCP buffer limits
#net.core.rmem_max = 8388608
#net.core.wmem_max = 8388608
#net.core.netdev_max_backlog = 5000
#net.ipv4.tcp_window_scaling = 1

# increase system file descriptor limit
fs.file-max = 65535

#Allow for more PIDs
kernel.pid_max = 65536

#Increase system IP port limits
net.ipv4.ip_local_port_range = 2000 65000

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