Simple DDOS Mitigation with iptables

edit /etc/sysctl.d/60-zercle.conf
and run
sysctl --system

# Kernel sysctl configuration file for Linux
# https://www.kernel.org/doc/Documentation/sysctl/
#
# Original by Michiel Klaver <https://klaver.it/linux/sysctl.conf>
# Modify by Kawin Viriyaprasopsook <[email protected]>
#
# The following is suitable for dedicated web server, mail, file server, KVM server etc.
# place file in /etc/sysctl.d/60-sysctl.conf
# and run sysctl –system
# ——————————————————————–
# System options
# ——————————————————————–
# Controls IP packet forwarding (Default 0 but docker,vpn,router server must set to 1)
net.ipv4.ip_forward = 0
net.ipv6.conf.all.forwarding = 0
# Addresses of mmap base, heap, stack and VDSO page are randomized
kernel.randomize_va_space = 2
# 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
# Allow for more PIDs
kernel.pid_max = 65535
# Changing Semaphore Limits
kernel.msgmni = 1024
kernel.sem = 250 256000 32 1024
# Controls the default maxmimum size of a mesage queue
kernel.msgmnb = 65535
# Controls the maximum size of a message, in bytes
kernel.msgmax = 65535
# Controls the maximum number of shared memory segments, in pages
kernel.shmall = 268435456
# Controls the maximum shared segment size, in bytes
kernel.shmmax = 268435456
# Keep at least 64MB of free RAM space available
vm.min_free_kbytes = 65535
# Controls source route verification
net.ipv4.conf.all.rp_filter = 2
net.ipv4.conf.default.rp_filter = 2
# Do not accept source routing
net.ipv4.conf.default.accept_source_route = 0
net.ipv6.conf.default.accept_source_route = 0
# Disable ICMP Redirect Acceptance
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.default.accept_redirects = 0
net.ipv4.conf.all.secure_redirects = 0
net.ipv4.conf.default.secure_redirects = 0
net.ipv6.conf.all.accept_redirects = 0
net.ipv6.conf.default.accept_redirects = 0
# Disable netfilter on bridges.
net.bridge.bridge-nf-call-ip6tables = 0
net.bridge.bridge-nf-call-iptables = 0
net.bridge.bridge-nf-call-arptables = 0
# Discourage Linux from swapping idle server processes to disk (default = 60)
vm.swappiness = 10
vm.dirty_ratio = 60
vm.dirty_background_ratio = 2
# RFC 1337 fix
net.ipv4.tcp_rfc1337 = 1
# Tweak how the flow of kernel messages is throttled.
#kernel.printk_ratelimit_burst = 10
#kernel.printk_ratelimit = 5
# ——————————————————————–
# The following allow the server to handle lots of connection requests
# ——————————————————————–
# See also http://www.nateware.com/linux-network-tuning-for-2013.html for
# an explanation about some of these parameters, and instructions for
# a few other tweaks outside this file.
# Protection from SYN flood attack.
net.ipv4.tcp_syncookies = 1
net.ipv4.tcp_syn_retries = 2
net.ipv4.tcp_synack_retries = 2
# Increase number of incoming connections that can queue up
# before dropping
net.core.somaxconn = 32768
# Handle SYN floods and large numbers of valid HTTPS connections
# https://shehab.tech/
net.ipv4.tcp_max_syn_backlog = 4096
# Increase the length of the network device input queue
net.core.netdev_max_backlog = 16384
# Increase system file descriptor limit so we will (probably)
# never run out under lots of concurrent requests.
# (Per-process limit is set in /etc/security/limits.conf)
fs.file-max = 209708
# Widen the port range used for outgoing connections
net.ipv4.ip_local_port_range = 1024 65535
# Increasing the amount of inotify watchers
fs.inotify.max_user_watches = 524288
# ——————————————————————–
# The following help the server efficiently pipe large amounts of data
# ——————————————————————–
# Disable source routing and redirects
net.ipv4.conf.all.send_redirects = 0
net.ipv4.conf.default.send_redirects = 0
net.ipv4.conf.all.accept_source_route = 0
net.ipv4.conf.default.accept_source_route = 0
net.ipv6.conf.all.accept_source_route = 0
net.ipv6.conf.default.accept_source_route = 0
# Avoid falling back to slow start after a connection goes idle
# keeps our cwnd large with the keep alive connections (kernel > 3.6)
net.ipv4.tcp_slow_start_after_idle = 0
# Controls TCP Packetization-Layer Path MTU Discovery
net.ipv4.tcp_mtu_probing = 1
# Turn on the tcp_window_scaling
net.ipv4.tcp_window_scaling = 1
# Turn on the tcp_timestamps, accurate timestamp make TCP congestion control algorithms work better
net.ipv4.tcp_timestamps = 1
# Enable the TCP selective acks option for better throughput
net.ipv4.tcp_sack = 1
# Change Congestion Control
# Use BBR TCP congestion control and set tcp_notsent_lowat to 16384 to ensure HTTP/2 prioritization works optimally
# Do a 'modprobe tcp_bbr' first (kernel > 4.9)
# Fall-back to htcp if bbr is unavailable (older kernels)
net.ipv4.tcp_congestion_control = htcp
net.ipv4.tcp_congestion_control = bbr
net.core.default_qdisc = fq
# bbr + fq_codel for kernel >= 4.13
#net.core.default_qdisc = fq_codel
net.ipv4.tcp_notsent_lowat = 16384
# Increase the maximum amount of option memory buffers
net.core.optmem_max = 65535
# Increase Linux autotuning TCP buffer limits
# Set max to 16MB (16777216) for 1GE and 32M (33554432) or 54M (56623104) for 10GE
# Don't set tcp_mem itself! Let the kernel scale it based on RAM.
# Increase the read-buffer space allocatable
net.ipv4.tcp_rmem = 8192 87380 33554432
net.ipv4.udp_rmem_min = 16384
net.core.rmem_default = 262144
net.core.rmem_max = 33554432
# Increase the write-buffer-space allocatable
net.ipv4.tcp_wmem = 8192 65536 33554432
net.ipv4.udp_wmem_min = 16384
net.core.wmem_default = 262144
net.core.wmem_max = 33554432
# If your servers talk UDP, also up these limits
net.ipv4.udp_rmem_min = 16384
net.ipv4.udp_wmem_min = 16384
# ——————————————————————–
# The following allow the server to handle lots of connection churn
# ——————————————————————–
# Increase the tcp-time-wait buckets pool size to prevent simple DOS attacks
net.ipv4.tcp_max_tw_buckets = 1440000
# Timeout broken connections faster (amount of time to wait for FIN)
net.ipv4.tcp_fin_timeout = 7
# Try to reuse time-wait connections, but don't recycle them (recycle can break clients behind NAT)
net.ipv4.tcp_tw_recycle = 0
net.ipv4.tcp_tw_reuse = 1
# Decrease the time default value for connections to keep alive
# Disconnect dead TCP connections after 600+(60*10) seconds
net.ipv4.tcp_keepalive_time = 600
net.ipv4.tcp_keepalive_probes = 60
net.ipv4.tcp_keepalive_intvl = 10
# This will enusre that immediatly subsequent connections use the new values
net.ipv4.route.flush = 1
net.ipv6.route.flush = 1

view raw
60-zercle.conf
hosted with ❤ by GitHub

/etc/iptables.up.rules

# Generated by iptables-save v1.6.0 on Thu Mar 30 00:19:26 2017
*raw
:PREROUTING ACCEPT [1324:102679]
:OUTPUT ACCEPT [110:12756]
# Don't track SYN packets
-A PREROUTING -p tcp -m tcp --tcp-flags FIN,SYN,RST,ACK SYN -j CT --notrack
COMMIT
# Completed on Thu Mar 30 00:19:26 2017
*mangle
:PREROUTING ACCEPT [1324:102679]
:INPUT ACCEPT [1248:94938]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [110:12756]
:POSTROUTING ACCEPT [110:12756]
# Allow loopback
-A PREROUTING -i lo -j ACCEPT
# Drop TCP packets that are new and are not SYN
-A PREROUTING -p tcp -m tcp ! --tcp-flags FIN,SYN,RST,ACK SYN -m conntrack --ctstate NEW -j DROP
# Drop SYN packets with suspicious MSS value
-A PREROUTING -p tcp -m conntrack --ctstate NEW -m tcpmss ! --mss 536:65535 -j DROP
# Block packets with bogus TCP flags
-A PREROUTING -p tcp -m tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG NONE -j DROP
-A PREROUTING -p tcp -m tcp --tcp-flags FIN,SYN FIN,SYN -j DROP
-A PREROUTING -p tcp -m tcp --tcp-flags SYN,RST SYN,RST -j DROP
-A PREROUTING -p tcp -m tcp --tcp-flags FIN,SYN FIN,SYN -j DROP
-A PREROUTING -p tcp -m tcp --tcp-flags FIN,RST FIN,RST -j DROP
-A PREROUTING -p tcp -m tcp --tcp-flags FIN,ACK FIN -j DROP
-A PREROUTING -p tcp -m tcp --tcp-flags ACK,URG URG -j DROP
-A PREROUTING -p tcp -m tcp --tcp-flags FIN,ACK FIN -j DROP
-A PREROUTING -p tcp -m tcp --tcp-flags PSH,ACK PSH -j DROP
-A PREROUTING -p tcp -m tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG FIN,SYN,RST,PSH,ACK,URG -j DROP
-A PREROUTING -p tcp -m tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG NONE -j DROP
-A PREROUTING -p tcp -m tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG FIN,PSH,URG -j DROP
-A PREROUTING -p tcp -m tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG FIN,SYN,PSH,URG -j DROP
-A PREROUTING -p tcp -m tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG FIN,SYN,RST,ACK,URG -j DROP
# Block spoofed packets
-A PREROUTING -s 224.0.0.0/3 -j DROP
-A PREROUTING -s 169.254.0.0/16 -j DROP
-A PREROUTING -s 172.16.0.0/12 -j DROP
-A PREROUTING -s 192.0.2.0/24 -j DROP
-A PREROUTING -s 192.168.0.0/16 -j DROP
-A PREROUTING -s 10.0.0.0/8 -j DROP
-A PREROUTING -s 0.0.0.0/8 -j DROP
-A PREROUTING -s 240.0.0.0/5 -j DROP
-A PREROUTING -s 127.0.0.0/8 ! -i lo -j DROP
# Drop fragments in all chains
-A PREROUTING -f -j DROP
COMMIT
# Completed on Thu Mar 30 00:19:26 2017
# Generated by iptables-save v1.6.0 on Tue Mar 28 11:50:15 2017
*nat
:INPUT ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:POSTROUTING ACCEPT [0:0]
:PREROUTING ACCEPT [0:0]
-A POSTROUTING -j MASQUERADE
COMMIT
# Completed on Thu Mar 30 00:19:26 2017
# Generated by iptables-save v1.6.0 on Tue Mar 28 11:50:15 2017
*filter
:INPUT ACCEPT [1246:94823]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [110:12756]
:port-scanning - [0:0]
# Allow loopback
-A INPUT -i lo -j ACCEPT
# Allow current connection
-A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
#Limiting the incoming icmp ping request: 
-A INPUT -p icmp -m limit --limit 1/s --limit-burst 2 -j ACCEPT
-A INPUT -p icmp -j DROP
# Simple DDOS Migation by SYNPROXY
-A INPUT -p tcp -m tcp -m conntrack --ctstate INVALID,UNTRACKED -j SYNPROXY --sack-perm --timestamp --wscale 7 --mss 1460 -m multiport --dports 22,80,443
-A INPUT -p tcp -m tcp -m conntrack --ctstate INVALID,UNTRACKED -j SYNPROXY --sack-perm --timestamp --wscale 7 --mss 1460 -m multiport --dports 8080,8443
-A INPUT -m conntrack --ctstate INVALID -j DROP
# SSH brute-force protection
-A INPUT -p tcp -m tcp --dport 22 -m conntrack --ctstate NEW -m recent --set --name SSHBF --rsource
-A INPUT -p tcp -m tcp --dport 22 -m conntrack --ctstate NEW -m recent --update --seconds 60 --hitcount 10 --name SSHBF --rsource -j DROP
# Protection against port scanning
-A port-scanning -p tcp -m tcp --tcp-flags FIN,SYN,RST,ACK RST -m limit --limit 1/sec --limit-burst 2 -j RETURN
-A port-scanning -j DROP
# Allow Apps
-A INPUT -p tcp -m tcp -m multiport -j ACCEPT --dports 22,80,443
-A INPUT -p tcp -m tcp -m multiport -j ACCEPT --dports 8080,8443
# Default DROP
-A INPUT -j DROP
COMMIT
# Completed on Thu Mar 30 00:19:26 2017

/etc/ip6tables.up.rules

# Generated by iptables-save v1.6.0 on Thu Mar 30 00:19:26 2017
*raw
:PREROUTING ACCEPT [1324:102679]
:OUTPUT ACCEPT [110:12756]
# Don't track SYN packets
-A PREROUTING -p tcp -m tcp --tcp-flags FIN,SYN,RST,ACK SYN -j CT --notrack
COMMIT
# Completed on Thu Mar 30 00:19:26 2017
# Generated by iptables-save v1.6.0 on Tue Mar 28 11:50:15 2017
*filter
:INPUT ACCEPT [1246:94823]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [110:12756]
:port-scanning - [0:0]
# Allow loopback
-A INPUT -i lo -j ACCEPT
# Allow current connection
-A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
-A FORWARD -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
#Limiting the incoming icmp ping request: 
-A INPUT -p ipv6-icmp -m limit --limit 1/s --limit-burst 2 -j ACCEPT
-A INPUT -p ipv6-icmp -j DROP
# Simple DDOS Migation by SYNPROXY
-A INPUT -p tcp -m tcp -m conntrack --ctstate INVALID,UNTRACKED -j SYNPROXY --sack-perm --timestamp --wscale 7 --mss 1460 -m multiport --dports 22,80,443
-A INPUT -p tcp -m tcp -m conntrack --ctstate INVALID,UNTRACKED -j SYNPROXY --sack-perm --timestamp --wscale 7 --mss 1460 -m multiport --dports 8080,8443
-A INPUT -m conntrack --ctstate INVALID -j DROP
# SSH brute-force protection
-A INPUT -p tcp -m tcp --dport 22 -m conntrack --ctstate NEW -m recent --set --name SSHBF --rsource
-A INPUT -p tcp -m tcp --dport 22 -m conntrack --ctstate NEW -m recent --update --seconds 60 --hitcount 10 --name SSHBF --rsource -j DROP
# Protection against port scanning
-A port-scanning -p tcp -m tcp --tcp-flags FIN,SYN,RST,ACK RST -m limit --limit 1/sec --limit-burst 2 -j RETURN
-A port-scanning -j DROP
# Allow Apps
-A INPUT -p tcp -m tcp -m multiport -j ACCEPT --dports 22,80,443
-A INPUT -p tcp -m tcp -m multiport -j ACCEPT --dports 8080,8443
# Default DROP
-A INPUT -j DROP
COMMIT
# Completed on Thu Mar 30 00:19:26 2017
# Generated by iptables-save v1.6.0 on Tue Mar 28 11:50:15 2017
*mangle
:PREROUTING ACCEPT [1324:102679]
:INPUT ACCEPT [1248:94938]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [110:12756]
:POSTROUTING ACCEPT [110:12756]
COMMIT
# Completed on Thu Mar 30 00:19:26 2017
# Generated by iptables-save v1.6.0 on Tue Mar 28 11:50:15 2017
*nat
:INPUT ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:POSTROUTING ACCEPT [0:0]
:PREROUTING ACCEPT [0:0]
-A POSTROUTING -j MASQUERADE
COMMIT
# Completed on Thu Mar 30 00:19:26 2017

Debian,Ubuntu load iptables
/etc/network/if-pre-up.d/iptablesload
chmod +x /etc/network/if-pre-up.d/iptablesload

#!/usr/bin/env bash
sysctl --system > /dev/null 2>&1
iptables-restore < /etc/iptables.up.rules
ip6tables-restore < /etc/ip6tables.up.rules
exit 0

RHEL,Centos load iptables

#!/usr/bin/env bash
sysctl --system > /dev/null 2>&1
systemctl mask firewalld
yum -y install iptables-services
systemctl enable iptables
systemctl enable ip6tables
iptables-restore < /etc/iptables.up.rules
ip6tables-restore < /etc/ip6tables.up.rules
ln -sf /etc/iptables.up.rules /etc/sysconfig/iptables
ln -sf /etc/ip6tables.up.rules /etc/sysconfig/ip6tables
exit 0
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