GRE tunnel issue

Mr Pro

4/21/24, 5:12 AM

I have 2 linux servers. I want to use server 1 ip for server 2 as a ddos protection, I have followed a tutorial online which works quite good but there is a small issue. While trying to do curl server1ip inside server 2 it gives me error connection timed out, while when doing curl server 1 ip from anywhere else apart from server 2 it works. Here is the commands i ran on server 1 :

echo 'net.ipv4.ip_forward=1' >> /etc/sysctl.conf
sysctl -p
iptunnel add gre1 mode gre local server1ip remote server2ip ttl 255
ip addr add 192.168.168.1/30 dev gre1
ip link set gre1 up
iptables -t nat -A POSTROUTING -s 192.168.168.0/30 ! -o gre+ -j SNAT --to-source server1ip
iptables -t nat -A PREROUTING -d server1ip -j DNAT --to-destination 192.168.168.2
iptables -A FORWARD -d 192.168.168.2 -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT

Here is the commands ran on server 2 :

iptunnel add gre1 mode gre local server2ip remote server1ip ttl 255
ip addr add 192.168.168.2/30 dev gre1
ip link set gre1 up
echo '100 BUYVM' >> /etc/iproute2/rt_tables
ip rule add from 192.168.168.0/30 table BUYVM
ip route add default via 192.168.168.1 table BUYVM

curl and ping doesn't work when i try to ping server1ip inside server2 it gives connection timed out. While i try to ping server1ip anywhere else it works.

0 + 0

linux

centos

gre

Elon Musk

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EN: GRE tunnel issue

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