RAWCOOKIE is a SYNPROXY module extension which moves initial SYN+ACK conversation into lower levels of kernel. It replaces original -j CT --notrack rule in iptables with RAWCOOKIE targes.

Original rules with SYNPROXY module:

iptables -t raw -A PREROUTING -i tge22 -p tcp -m tcp --syn --dport 80 -j CT --notrack
iptables -A INPUT -i tge22 -p tcp -m tcp --dport 80 -m state --state INVALID,UNTRACKED -j SYNPROXY --sack-perm --timestamp --wscale 7 --mss 1460
iptables -A INPUT -i tge22 -p tcp -m tcp --dport 80 -m state --state INVALID -j DROP

Must be replaced with:

iptables -t raw -A PREROUTING -i tge22 -p tcp -m tcp --syn --dport 80 -j RAWCOOKIE --sack-perm --timestamp --wscale 7 --mss 1460 --senddirect
iptables -A INPUT -i tge22 -p tcp -m tcp --dport 80 -m state --state INVALID,UNTRACKED -j SYNPROXY --sack-perm --timestamp --wscale 7 --mss 1460
iptables -A INPUT -i tge22 -p tcp -m tcp --dport 80 -m state --state INVALID -j DROP

RAWCOOKIE module supports special mode for sending initial SYN+ACK packet when the packet avoids Linux routing system. The SYN+ACK packet is send directly to the MAC addres (the address of the router) which we received the original SYN packet from. The direct mode can be enable via --senddirect option.

In case when it is necessary to override the destination MAC address there is option --txmac which can do it for you.

--txmac 4c:ae:a3:6a:80:bc

NOTE: Please do not set --txmac option if you are not sure how this option works. By setting invalid/not existing MAC address you might flood packets to all ethernet ports whet the server is connected to!

# git clone https://github.com/netx-as/xt_RAWCOOKIE.git
# cd xt_RAWCOOKIE
# make
# make install

It is required to have kernel and iptables sources installed.

For sources please visit: https://github.com/netx-as/xt_RAWCOOKIE

RAWCOKIE module is based on Linux SYNCOKIE module as is provided under same license as the SYNCOOKIE module.