server sending TCP RST / reset by peer

[seek2222]

HI all,

I have a problem that the server is sending TCP RST toward the client. I have gone through the logs and I couldn't find the root cause of sending the RST.

tshark/tcpdump from server:
36 31.420796365 SERVER_IP → CLIENT_IP TCP 54 443 → 53520 [RST, ACK] Seq=1 Ack=1 Win=65535 Len=0
37 31.663715425 CLIENT_IP → SERVER_IP TCP 78 53530 → 443 [SYN] Seq=0 Win=42340 Len=0 MSS=1460 SACK_PERM TSval=717831679 TSecr=0 WS=2048 TFO=R

server:
RUST_LOG=info /root/phantun/target/release/server --local 443 --remote 127.0.0.1:51822 &> /var/log/phantun_server.log &

~# tail -f /var/log/phantun_server.log
INFO server > Remote address is: 127.0.0.1:51822
INFO server > 1 cores available
INFO server > Created TUN device tun0
INFO server > Listening on 443

client:
RUST_LOG=info /root/phantun/target/release/client --local 127.0.0.1:1234 --remote SERVER_IP:443 &> /var/log/phantun_client.log &

INFO client > New UDP client from 127.0.0.1:46180
INFO fake_tcp > Sent SYN to server
INFO fake_tcp > Connection to SERVER_IP:443 established
INFO fake_tcp > Connection (Fake TCP connection from 192.168.200.2:27979 to SERVER_IP:443) reset by peer
INFO fake_tcp > Fake TCP connection to (Fake TCP connection from 192.168.200.2:27979 to SERVER_IP:443) closed

server iptables:
iptables -t filter -nvL
Chain INPUT (policy ACCEPT 530K packets, 197M bytes)
pkts bytes target prot opt in out source destination
Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
562 22480 ACCEPT 0 -- tun0 * 0.0.0.0/0 0.0.0.0/0
562 35940 ACCEPT 0 -- * tun0 0.0.0.0/0 0.0.0.0/0

Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination

iptables -t nat -nvL
Chain PREROUTING (policy ACCEPT 365K packets, 28M bytes)
pkts bytes target prot opt in out source destination
1083 68296 DNAT 6 -- eth0 * 0.0.0.0/0 0.0.0.0/0 tcp dpt:443 to:192.168.201.2

any input is much appreciated.
P.s, the 443 TCP/udp port is free from the netstat side as well. I know already that the phantun is not registering the listening port on Kernel.

[smith752]

Check whether system kernel forwarding is turned on, the server side and client side the value of net.ipv4.ip_forward should be equal 1
# sysctl -a | grep "net.ipv4.ip_forward"
net.ipv4.ip_forward = 1

you can execute this command to turn on kernel forwarding
echo "net.ipv4.ip_forward = 1">>/etc/sysctl.conf;sysctl -p

[seek2222]

@smith752 first off, thanks for replying.
secondly, the ipv4 forwarding is enabled on both phantun client and server.

[seek2222]

my server is running Ubuntu 22.04 and on another instance it is running on 24.04 with latest kernel installed.