Can not redirect data package from wlan0 to local proxy service port 12345 by iptables

Question

That is my iptables config:

Chain PREROUTING (policy ACCEPT 3187 packets, 517K bytes)
 pkts bytes target     prot opt in     out     source               destination         
  295 17664 LOG        tcp  --  wlan0  any     anywhere             anywhere             LOG level warn prefix "REDIRECT: "
  420 25164 REDIRECT   tcp  --  wlan0  any     anywhere             anywhere             redir ports 12345

Chain INPUT (policy ACCEPT 9561 packets, 686K bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain OUTPUT (policy ACCEPT 8212 packets, 530K bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain POSTROUTING (policy ACCEPT 1805 packets, 136K bytes)
 pkts bytes target     prot opt in     out     source               destination         
  125 23839 MASQUERADE  all  --  any    eth0    anywhere             anywhere 

My port is listening:

sudo netstat -tuln | grep 12345
tcp        0      0 127.0.0.1:12345         0.0.0.0:*               LISTEN     
tcp6       0      0 ::1:12345               :::*                    LISTEN  

My network adapter:

 ifconfig
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.88.18  netmask 255.255.255.0  broadcast 192.168.88.255
        inet6 fe80::abd9:66a6:2c42:a8b8  prefixlen 64  scopeid 0x20<link>
        ether 2c:cf:67:05:fd:9f  txqueuelen 1000  (Ethernet)
        RX packets 2123715  bytes 799360843 (762.3 MiB)
        RX errors 0  dropped 155  overruns 0  frame 0
        TX packets 903629  bytes 147497164 (140.6 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 1000  (Local Loopback)
        RX packets 1498324  bytes 126327145 (120.4 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 1498324  bytes 126327145 (120.4 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

wlan0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.4.1  netmask 255.255.255.0  broadcast 192.168.4.255
        inet6 fe80::2ecf:67ff:fe05:fda0  prefixlen 64  scopeid 0x20<link>
        ether 2c:cf:67:05:fd:a0  txqueuelen 1000  (Ethernet)
        RX packets 120878  bytes 25247289 (24.0 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 150299  bytes 107686413 (102.6 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

wlan1: flags=4099<UP,BROADCAST,MULTICAST>  mtu 2312
        ether d8:44:89:de:24:b3  txqueuelen 1000  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

When I use curl -x socks5://127.0.0.1:12345 www.google.com to test, the proxy works.

But when I use my app, the network adapter wlan0 receives data but cannot redirect it to local port 12345.

I think there might be an issue with iptables.

Does anyone have any ideas?

Answer 1

Did you enable IPv4 packet forwarding in sysctl? If not, try this:

sudo sysctl net.ipv4.ip_forward=1
sudo sysctl -p