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Complete Traffic Forwarding Guide (iptables)

This guide explains how to use IP forwarding and iptables NAT to redirect incoming traffic from a Linux relay server to a 4iProto destination server. Typical use cases include full traffic forwarding, transparent proxy setups, and gateway relay designs.

:::info Alternative For a dedicated Abdal 4iProto Multi-Hop TCP/UDP proxy (without writing iptables rules yourself), see Abdal 4iProto Proxy Multi-Hop. :::

Complete Traffic Forwarding Guide from an Entry Server to 4iProto Server using iptables

danger

Apply these rules carefully. Incorrect NAT rules can lock you out of the relay host. Keep an alternate SSH path ready before changing PREROUTING rules.

Prerequisites​

  • Linux operating system
  • Root access
  • iptables installed and active
  • Valid 4iProto server IP
  • Basic understanding of NAT, DNAT, SNAT, and routing

Step 1: Enable IP Forwarding​

echo "net.ipv4.ip_forward=1" >> /etc/sysctl.conf
sysctl -p

Step 2: Redirect SSH Port to Another Server​

Keep management access reachable by redirecting SSH intentionally (replace placeholders):

iptables -t nat -A PREROUTING -p tcp --dport 22 -j DNAT --to-destination IRAN_IP

Step 3: Forward All Traffic to 4iProto Server​

iptables -t nat -A PREROUTING -j DNAT --to-destination 4iProto_IP

Step 4: Enable Source NAT​

iptables -t nat -A POSTROUTING -j MASQUERADE

Important Notes​

  • The SSH port rule must be applied before the general PREROUTING rule
  • Ensure alternative SSH access before applying rules
  • Adjust firewall settings if you use firewalld or ufw
  • Replace IRAN_IP and 4iProto_IP with real addresses for your topology