port forwarding to application in network namespace with vpn
I was able to set up a network namespace, establish a tunnel with openvpn and start an application that uses this tunnel inside the namespace. So far so good, but this application can be accessed via a web interface and I cant’t figure out how to route requests to the web interface inside my LAN.
I followed a guide from @schnouki explaining how to set up a network namespace and run OpenVPN inside of it
ip netns add myvpn ip netns exec myvpn ip addr add 127.0.0.1/8 dev lo ip netns exec myvpn ip link set lo up ip link add vpn0 type veth peer name vpn1 ip link set vpn0 up ip link set vpn1 netns myvpn up ip addr add 10.200.200.1/24 dev vpn0 ip netns exec myvpn ip addr add 10.200.200.2/24 dev vpn1 ip netns exec myvpn ip route add default via 10.200.200.1 dev vpn1 iptables -A INPUT ! -i vpn0 -s 10.200.200.0/24 -j DROP iptables -t nat -A POSTROUTING -s 10.200.200.0/24 -o en+ -j MASQUERADE sysctl -q net.ipv4.ip_forward=1 mkdir -p /etc/netns/myvpn echo 'nameserver 8.8.8.8' > /etc/netns/myvpn/resolv.conf
After that, I can check my external ip and get different results inside and outside of the namespace, just as intended:
curl -s ipv4.icanhazip.com <my-isp-ip> ip netns exec myvpn curl -s ipv4.icanhazip.com <my-vpn-ip>
The application is started, I’m using deluge for this example. I tried several applications with a web interface to make sure it’s not a deluge specific problem.
ip netns exec myvpn sudo -u <my-user> /usr/bin/deluged ip netns exec myvpn sudo -u <my-user> /usr/bin/deluge-web -f ps $(ip netns pids myvpn) PID TTY STAT TIME COMMAND 1468 ? Ss 0:13 openvpn --config /etc/openvpn/myvpn/myvpn.conf 9302 ? Sl 10:10 /usr/bin/python /usr/bin/deluged 9707 ? S 0:37 /usr/bin/python /usr/bin/deluge-web -f
I’m able to access the web interface on port 8112 from within the namespace and from outside if I specify the ip of veth vpn1.
ip netns exec myvpn curl -Is localhost:8112 | head -1 HTTP/1.1 200 OK ip netns exec myvpn curl -Is 10.200.200.2:8112 | head -1 HTTP/1.1 200 OK curl -Is 10.200.200.2:8112 | head -1 HTTP/1.1 200 OK
But I do want to redirect port 8112 from my server to the application in the namespace. The goal is to open a browser on a computer inside my LAN and get the web interface with http://my-server-ip:8112 (my-server-ip being the static ip of the server that instantiated the network interface)
EDIT: I removed my attempts to create iptables rules. What I’m trying to do is explained above and the following commands should output a HTTP 200:
curl -I localhost:8112 curl: (7) Failed to connect to localhost port 8112: Connection refused curl -I <my-server-ip>:8112 curl: (7) Failed to connect to <my-server-ip> port 8112: Connection refused
I tried DNAT and SNAT rules and threw in a MASQUERADE for good measure, but since I don’t know what I’m doing, my attempts are futile. Perhaps someone can help me put together this construct.
EDIT: The tcpdump output of tcpdump -nn -q tcp port 8112. Unsurprisingly, the first command returns a HTTP 200 and the second command terminates with a refused connection.
curl -Is 10.200.200.2:8112 | head -1 listening on vpn0, link-type EN10MB (Ethernet), capture size 262144 bytes IP 10.200.200.1.36208 > 10.200.200.2.8112: tcp 82 IP 10.200.200.2.8112 > 10.200.200.1.36208: tcp 145 curl -Is <my-server-ip>:8112 | head -1 listening on lo, link-type EN10MB (Ethernet), capture size 262144 bytes IP <my-server-ip>.58228 > <my-server-ip>.8112: tcp 0 IP <my-server-ip>.8112 > <my-server-ip>.58228: tcp 0
EDIT: @schnouki himself pointed me to a Debian Administration article explaining a generic iptables TCP proxy. Applied to the problem at hand, their script would look like this:
YourIP=<my-server-ip> YourPort=8112 TargetIP=10.200.200.2 TargetPort=8112 iptables -t nat -A PREROUTING --dst $YourIP -p tcp --dport $YourPort -j DNAT --to-destination $TargetIP:$TargetPort iptables -t nat -A POSTROUTING -p tcp --dst $TargetIP --dport $TargetPort -j SNAT --to-source $YourIP iptables -t nat -A OUTPUT --dst $YourIP -p tcp --dport $YourPort -j DNAT --to-destination $TargetIP:$TargetPort
Unfortunately, traffic between the veth interfaces seized and nothing else happened. However, @schnouki also suggested the use of
socat as a TCP proxy and this is working perfectly.curl -Is <my-server-ip>:8112 | head -1 IP 10.200.200.1.43384 > 10.200.200.2.8112: tcp 913 IP 10.200.200.2.8112 > 10.200.200.1.43384: tcp 1495
I have yet to understand the strange port shuffling while traffic is traversing through the veth interfaces, but my problem is solved now.
Answers:
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Method 1
Interconnecting network namespace with main namespace always bothers me.
The reason I usually create a namespace is because I want it isolated.
Depending on what it is you are trying to achieve with namespaces creating interconnects can defeat that purpose.
But even isolated I still want to poke it over the network, for convenience.
This solution lets you keep isolation and forward some connections to it anyway.
You don’t need to create all that network between the two network namespaces just to forward one port.
Run this in the namespace where you want to accept connections.
Must be run as root for ip netns exec to work.
socat tcp-listen:8112,fork,reuseaddr exec:'ip netns exec myvpn socat STDIO "tcp-connect:127.0.0.1:8112"',nofork
It listens for connections in one network namespace where you run it, on port 8112, then connected client gets
exec to run ip netns exec myvpn ... to execute the rest inside the myvpn network namespace, then once inside the myvpn network namespace it creates second connection again with another socat.Or run it as systemd service
This also uses socat.
Create service config file /etc/systemd/system/deluge-web-netns.service with content:
[Unit] Description=Forwarder to deluge-web in netns After=network-online.target #Requires=deluge-web.service #After=deluge-web.service [Service] Type=simple ExecStart=/usr/bin/socat tcp-listen:8112,fork,reuseaddr exec:'ip netns exec vpn-netns socat STDIO "tcp-connect:127.0.0.1:8112"',nofork #User=deluge #Group=deluge SyslogIdentifier=deluge-web-fwd Restart=on-failure # Time to wait before forcefully stopped. TimeoutStopSec=300 [Install] WantedBy=multi-user.target
Check/Fix the value in
ExecStart=/path/to/socat to “be an absolute path to an executable” as required by man systemd.service.Consider setting correct values and enabling the directives Requires and After.
Then enable and start with commands:
systemctl daemon-reload systemctl enable deluge-web-netns systemctl start deluge-web-netns
Or run it under xinetd
This also uses socat.
create conf file, e.g. /etc/xinetd.d/deluge-web-fwd with content
service deluge-web-vpn-netns
{
type = UNLISTED
socket_type = stream
protocol = tcp
port = 8112
flags = IPv4 KEEPALIVE
wait = no
user = root
server = /sbin/ip
server_args = netns exec vpn-netns socat STDIO tcp-connect:127.0.0.1:8112
}Restart
xinetdservice xinetd restart
Program
ncat can also be used similar to socat.Method 2
I’ve always had issues with iptables redirections (probably my fault, I’m pretty sure it’s doable). But for a case like yours, it’s IMO easier to do it in user-land without iptables.
Basically, you need to have a daemon in your “default” workspace listening on TCP port 8112 and redirecting all traffic to 10.200.200.2 port 8112. So it’s a simple TCP proxy.
Here’s how to do it with socat:
socat tcp-listen:8112,reuseaddr,fork tcp-connect:10.200.200.2:8112
(The
fork option is needed to avoid socat from stopping after the first proxied connection is closed).EDIT: added reuseaddr as suggested in the comments.
If you absolutely want to do it with iptables, there’s a guide on the Debian Administration site. But I still prefer socat for more advanced stuff — like proxying IPv4 to IPv6, or stripping SSL to allow old Java programs to connect to secure services…
Beware however that all connections in Deluge will be from your server IP instead of the real client IP. If you want to avoid that, you will need to use a real HTTP reverse proxy that adds the original client IP to the proxied request in a HTTP header.
Method 3
For deluge here is my solution. No need for iptables. Here are the steps:
- Start your openvpn tunnel
- Create namespace and bring your openvpn tunnel there:
ip netns add $NS # Wait for the TUN to come up while [[ $(ip route|grep $TUN|wc -l) == 0 ]]; do sleep 1; done MY_IP=$(ip addr show $TUN|grep inet|cut -d' ' -f6|cut -d'/' -f1) # The way you extract gateway IP might be different for your openvpn connection GATEWAY_IP=$MY_IP # jail my $TUN (VPN interface) into the namespace ip link set $TUN netns $NS # Bring the interface up with a subnet (equivalent to the one given to me by VPN server) ip netns exec $NS ifconfig $TUN $MY_IP/24 up # Bring loopback up ip netns exec $NS ifconfig lo 127.0.0.1/8 up # Set up remote gateway (your pointtopoint VPN IP address) ip netns exec $NS route add default gw $GATEWAY_IP
- Establish veth connection between your default namespace and the one you’ve created:
# Set up veth interfaces for communication between namespaces ip link add veth0 type veth peer name veth1 # Move the second veth to your namespace ip link set veth1 netns $NS # give an IP from unused IP range to first veth ifconfig veth0 10.1.1.1/24 up # And the second one ip netns exec $NS ifconfig veth1 10.1.1.2/24 up # TODO: set up a bridge between veth1 and eth interface to let it communicate with LAN # Set up DNS client. ip netns will emulate /etc/resolv.conf using this file: mkdir -p /etc/netns/$NS echo "nameserver 8.8.4.4" >/etc/netns/$NS/resolv.conf
- Run your deluged in the $NS and your deluge-web in your default namespace. Point deluge-web to the 10.1.1.2 veth IP address, where deluged will be listening for its connection.
Voila! You’ve got deluged secured behind the VPN while your deluge-web is freely accessible on your home network
Method 4
@AndrDevEK’s answer is useful. To expand upon that, you may not want to install socat. In which case you can achieve the same thing with a slightly convoluted SSH port-forward setup. In particular the feature of port-forwarding to/from a unix-domain socket is useful here, because unix-domain sockets operate independently of network namespaces:
sudo ip netns exec myvpn su -c "ssh -N -L /tmp/myunixsock:localhost:8112 localhost" $USER & ssh_pid1=$! ssh -N -L localhost:8112:/tmp/myunixsock localhost & ssh_pid2=$!
Cleanup:
sudo kill $ssh_pid1 kill $ssh_pid2 rm /tmp/myunixsock
The first
ssh -N -L is started within the myvpn namespace. This creates a unix-domain socket /tmp/myunixsock and listens on it. Incoming connections are forwarded to localhost:8112 (inside the myvpn namespace).The second
ssh -N -L is started in the default namespace. This creates a listening TCP port and forwards incoming connections to the unix-domain socket.It should be noted that in order for this to work, ssh inside your network namespace will need to be working if it is not already (and passwordless pubkey operation is helpful):
sudo ip netns exec myvpn ip link set up dev lo sudo ip netns exec myvpn /usr/sbin/sshd -o PidFile=/run/sshd-myvpn.pid ssh-copy-id localhost
All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0
