#DOP ICMP Echo-Request Messages Sent to Broadcast Or Multicast Addresses
Echo 1> / proc / sys / net / ipv4 / icmp_echo_ignore_broadcasts
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#Drop Source Routed Packets
Echo 0> / proc / sys / net / ipv4 / conf / all / accept_source_route
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# Enable TCP SYN Cookie Protection from Syn Floods
Echo 1> / Proc / Sys / Net / IPv4 / TCP_Syncookies
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# Don't accept ICMP Redirect Messages
Echo 0> / Proc / Sys / Net / IPv4 / Conf / All / Accept_Redirects
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# Don't send ICMP Redirect Messages
Echo 0> / proc / sys / net / ipv4 / conf / all / send_redirects
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# Enable Source Address Spoofing Protection
ECHO 1> / proc / sys / net / ipv4 / conf / all / rp_filter
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# Log Packets with Impossible Source Addresses
Echo 1> / Proc / Sys / Net / IPv4 / Conf / All / Log_martians
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# Flush all chains
/ sbin / iptables - Flush
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# Allow unlimited traffic on the loopback interface
/ sbin / iptables -a input -i lo -j acceptpt
/ sbin / iptables -a output -o lo -j acid
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# Set default policies
/ sbin / iptables -p input drop
/ sbin / iptables -P Output Drop
/ sbin / iptables -p forward Drop
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# Previously initiated and accountted Exchanges Bypass Rule Checking
# Allow unlimited Outbound Traffic
/ sbin / iptables -ainput -m state --state established, Related -j Accept
/ sbin / iptables -a output -m state --state new, established, related -j accept
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#Enable ssh port 22
/ sbin / iptables -a input -p tcp --dport 22 -m state --state new -j acceptpt
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# Drop All other traffic
/ sbin / iptables -a input -j drop
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The above instance is to establish a firewall, turn on the SSH port to the outside, and turn off the ICMP package.
