DDOS Attack Fix

1. Track which IP address in the server is targeted by the ddos attack
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netstat -plan | grep :80 | awk ‘{print $4}’ | cut -d: -f1 |sort |uniq -c
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2. Detect from which IPs, the attack is coming
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netstat -plan | grep :80 | awk ‘{print $5}’ | cut -d: -f1 |sort |uniq -c
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3. Edit /etc/csf/csf.conf
* SYNFLOOD
SYNFLOOD is disabled by default. If you are not receiving any sort of attack, there is no need to enable it. If you are expecting an attack, enable it and set the rules like
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SYNFLOOD = “1″
SYNFLOOD_RATE = “30/s”
SYNFLOOD_BURST = “10″
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i.e. if 30 connections are received from an IP/sec for 10 times, block it. Make sure don’t keep it too strict if you are not receiving an attack else it will generate false positives and will block legit connections.
*PORTFLOOD
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PORTFLOOD = 80;tcp;100;5,22;tcp;5;300
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ie, If an IP makes 100 connections in 5 sec to port 80 (tcp), then it will be blocked from the server and if 5 connections in 300 sec to 22 port.
4. Edit /etc/sysctl.conf
Paste the following into the file, you can overwrite the current information.
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#Kernel sysctl configuration file for Red Hat Linux
#
# For binary values, 0 is disabled, 1 is enabled. See sysctl(8) and
# sysctl.conf(5) for more details.
# Disables packet forwarding
net.ipv4.ip_forward=0
# Disables IP source routing
net.ipv4.conf.all.accept_source_route = 0
net.ipv4.conf.lo.accept_source_route = 0
net.ipv4.conf.eth0.accept_source_route = 0
net.ipv4.conf.default.accept_source_route = 0
# Enable IP spoofing protection, turn on source route verification
net.ipv4.conf.all.rp_filter = 1
net.ipv4.conf.lo.rp_filter = 1
net.ipv4.conf.eth0.rp_filter = 1
net.ipv4.conf.default.rp_filter = 1
# Disable ICMP Redirect Acceptance
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.lo.accept_redirects = 0
net.ipv4.conf.eth0.accept_redirects = 0
net.ipv4.conf.default.accept_redirects = 0
# Enable Log Spoofed Packets, Source Routed Packets, Redirect Packets
net.ipv4.conf.all.log_martians = 0
net.ipv4.conf.lo.log_martians = 0
net.ipv4.conf.eth0.log_martians = 0
# Disables IP source routing
net.ipv4.conf.all.accept_source_route = 0
net.ipv4.conf.lo.accept_source_route = 0
net.ipv4.conf.eth0.accept_source_route = 0
net.ipv4.conf.default.accept_source_route = 0
# Enable IP spoofing protection, turn on source route verification
net.ipv4.conf.all.rp_filter = 1
net.ipv4.conf.lo.rp_filter = 1
net.ipv4.conf.eth0.rp_filter = 1
net.ipv4.conf.default.rp_filter = 1
# Disable ICMP Redirect Acceptance
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.lo.accept_redirects = 0
net.ipv4.conf.eth0.accept_redirects = 0
net.ipv4.conf.default.accept_redirects = 0
# Disables the magic-sysrq key
kernel.sysrq = 0
# Decrease the time default value for tcp_fin_timeout connection
net.ipv4.tcp_fin_timeout = 15
# Decrease the time default value for tcp_keepalive_time connection
net.ipv4.tcp_keepalive_time = 1800
# Turn off the tcp_window_scaling
net.ipv4.tcp_window_scaling = 0
# Turn off the tcp_sack
net.ipv4.tcp_sack = 0
# Turn off the tcp_timestamps
net.ipv4.tcp_timestamps = 0
# Enable TCP SYN Cookie Protection
net.ipv4.tcp_syncookies = 1
# Enable ignoring broadcasts request
net.ipv4.icmp_echo_ignore_broadcasts = 1
# Enable bad error message Protection
net.ipv4.icmp_ignore_bogus_error_responses = 1
# Log Spoofed Packets, Source Routed Packets, Redirect Packets
net.ipv4.conf.all.log_martians = 1
# Increases the size of the socket queue (effectively, q0).
net.ipv4.tcp_max_syn_backlog = 1024
# Increase the tcp-time-wait buckets pool size
net.ipv4.tcp_max_tw_buckets = 1440000
# Allowed local port range
net.ipv4.ip_local_port_range = 16384 65536
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Run /sbin/sysctl -p and sysctl -w net.ipv4.route.flush=1 to enable the changes without a reboot.
* TCP Syncookies
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echo 1 > /proc/sys/net/ipv4/tcp_syncookies
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5. In addition to the above you can also add Some IPTABLES Rules:
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iptables -A INPUT -p tcp –syn -m limit –limit 1/s –limit-burst 3 -j RETURN
iptables -A INPUT -p tcp –syn -m state –state ESTABLISHED,RELATED –dport 80 -m limit –limit 1/s –limit-burst 2 -j ACCEPT
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