Forward Traffic Between Ports

Scenario

A service on your server is running on port 8080, but you now need it to also be reachable on port 8081. The application cannot be restarted and its configuration cannot be changed.

Task

Verify the service is listening on 127.0.0.1:8080. Configure iptables to forward all TCP traffic from port 8081 to port 8080, ensuring this works for both external requests and local connections (localhost). Verify the forwarding works, then save the rules to persist after a reboot using iptables-save

Example

tcp        0      0 127.0.0.1:8080          0.0.0.0:*               LISTEN      1234/java

PREROUTING (policy ACCEPT)
REDIRECT   tcp  --  0.0.0.0/0   0.0.0.0/0   tcp dpt:8081 redir ports 8080

OUTPUT (policy ACCEPT)
REDIRECT   tcp  --  0.0.0.0/0   127.0.0.1   tcp dpt:8081 redir ports 8080

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