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Proxy to TCP port with real IP (self.selfhosted)

submitted 1 year ago by nickshanks to c/selfhosted

33 comments fedilink hide all child comments

Simple question, difficult solution. I can't work it out. I have a server at home with a site-to-site VPN to a server in the cloud. The server in the cloud has a public IP.

I want people to access server in the cloud and it should forward traffic through the VPN. I have tried this and it works. I've tried with nginx streams, frp and also HAProxy. They all work, but, in the server at home logs I can only see that people are connecting from the site-to-site VPN, not their actual source IP.

Is there any solution (program/Docker image) that will take a port, forward it to another host (or maybe another program listening on the host) that then modifies the traffic to contain the real source IP. The whole idea is that in the server logs I want to see people's real IP addresses, not the server in the cloud private VPN IP.

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[–] [email protected] 3 points 1 year ago* (last edited 1 year ago) (12 children)

Is there any solution (program/Docker image) that will take a port, forward it to another host (or maybe another program listening on the host) that then modifies the traffic to contain the real source IP. The whole idea is that in the server logs I want to see people’s real IP addresses, not the server in the cloud private VPN IP.

Not that I'm aware of. Most methods require some kind of out-of-band way to send the client's real IP to the server. e.g. X-Forwarded-For headers, Proxy Protocol, etc.

If your backend app supports proxy protocol, you may be able to use HAProxy in front on the VPS and use proxy protocol from there to the backend. Nginx may also support this for streams (I don't recall if it does or not since I mainly use HAProxy for that).

Barring that, there is one more way, but it's less clean.

You can use iptables on the VPS to do a prerouting DNAT port forward. The only catch to this is that the VPN endpoint that hosts the service must have its default gateway set to the VPN IP of the VPS, and you have to have a MASQUERADE rule so traffic from the VPN can route out of the VPS. I run two services in this configuration, and it works well.

iptables -t nat -A PREROUTING -d {VPS_PUBLIC_IP}/32 -p tcp -m tcp --dport {PORT} -j DNAT --to-destination {VPN_CLIENT_ADDRESS}
iptables -t nat -A POSTROUTING -s {VPN_SUBNET}/24 -o eth0 -j MASQUERADE

Where eth0 is the internet-facing interface of your VPS.

Edit: One more catch to the port forward method. This forward happens before the traffic hits your firewall chain on the VPS, so you'd need to implement any firewalls on the backend server.

[–] nickshanks 1 points 1 year ago (10 children)

Thank you so much for the quick and detailed reply, appreciate it!

Done all of the iptables stuff, just trying to change the default gateway on the server at home now:

network:
  version: 2
  renderer: networkd
  ethernets:
    eth0:
      dhcp4: true
      routes:
        - to: 0.0.0.0/0
          via: <vps public ip>

Does the above netplan yaml look right? When it's applied, I can't access the internet or even the VPS public IP.

[–] nickshanks 0 points 1 year ago (2 children)

Do I need to specify to forward VPN traffic through my router and then traffic to 0.0.0.0/0 through the VPN?

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