#We told the firewall to take all incoming packets with tcp flags NONE and just DROP them. Is a localhost interface iptables -A INPUT -i lo -j ACCEPT #Now we can start adding selected services to our firewall filter. Also destination machine will try to reply from port 22 but tcp connection. ![]() #- Use Selective ACK which can be used to signify that specific packets are missing Hence it would not recognize this reply and send TCP reset. TCP sequence numbers enable /proc /sys /net /ipv4 /tcp_syncookies #- Help against syn-flood DoS or DDoS attacks using particular choices of initial #- Protect against wrapping sequence numbers and aid round trip time measurementĮnable /proc /sys /net /ipv4 /tcp_timestamps #- Ignore packets with impossible addressesĭisable /proc /sys /net /ipv4 /conf /*/log_martians In order to point it to 192.168.2. #- As we don't accept redirects, don't send Redirect messages eitherĭisable /proc /sys /net /ipv4 /conf /*/send_redirects iptables -A INPUT -i tap+ -j ACCEPT iptables -A FORWARD -i tap+ -j ACCEPT iptables -t nat -A POSTROUTING -s 192.168.2.0/24 -o eth0 -j MASQUERADE On the client, the default remains to route via 192.168.1.1. #- Disable ICMP redirect acceptance which can be used to alter your routing tablesĭisable /proc /sys /net /ipv4 /conf /*/accept_redirects Purposes disable /proc /sys /net /ipv4 /conf /*/accept_source_route Source routing is rarely used for legitimate Safer, but breaks asymmetric routing and/or IPSECĮnable /proc /sys /net /ipv4 /conf /*/rp_filter #- Enable bad error message protectionĮnable /proc /sys /net /ipv4 /icmp_ignore_bogus_error_responses Now to end, let’s refuse all unawolled incoming connections and let’s allow all outgoing traffic: The fifth line, which belongs to the 22-protection chain, says to drop CONNECTIONS if they seem to be over 3 times within 30 seconds. ![]() The fourth line says if the CONNECTIONS weren’t seen over 3 times within 30 seconds, they could be accepted. The third line says if a CONNECTIONS is over 3 times within 30 seconds, the firewall continues applying the chain 22-protection. The second line says packets netmask 255.255.255.255 are named as CONNECTIONS. In the first liNe, our rule says “ -m conntrack –ctstate NEW,” which means if the connection is new, then pass to the rule “22-test”. rsource -seconds 30 -hitcount 3 -j 22-protection Iptables -A 22-test -m recent -name CONNECTIONS -rcheck -mask 255.255.255.255 Iptables -A 22-test -m recent -name CONNECTIONS -set -mask 255.255.255.255 -rsource Iptables -A INPUT -p tcp -m tcp -dport 22 -m conntrack -ctstate NEW -j 22-test #Protect your SSH Service against brute force attacks by limiting connection attempts To access iptables -A INPUT -p tcp -s X.X.X.X -dport 22 -m conntrack -ctstate NEW, Then use DNAT to forward traffic over the VPN and source IP based routing to bring the replies back to the NAT.#Protect your SSH Service against brute force attacks by allowing only a specific IP That will make abuse control very difficult.Īnother soloution to points 2 and 3 would be to set up a VPN between the two servers. You can work arround points 2 and 3 by using a SNAT or MASQURADE rule in addition to the DNAT but if you do that then you lose the original source IP of the traffic. Otherwise the client will get a response with the wrong source IP/port which it is likely to drop (if it has not already been dropped by reverse path filtering). and if i type : iptables -t nat -F PREROUTING iptables -t nat -A PREROUTING -d 10.8.1.0/24 -j DNETMAP -prefix 192.168.15.0/24 nothing happen. Responses to packets that go through a NAT must go through the same NAT so the reverse translation can be performed. iptables -t nat -A PREROUTING -d 10.8.1.173/32 -j DNAT -to-destination 192.168.15.173.After being natted and placed back on the network the packet may fall victim to source address filtering as it looks very much like a spoofed packet.There are three potential problems I see (contary to the other answer I don't see anything that would cause a "loop" even in the unedited version of your question).
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