Using OpenVPN connection to play games while abroad using Stream's In-Home Streaming

  • 10 min read

    • Introduction

    Steam has a great (albeit, a little glitchy) feature called In-Home Streaming that allows you to stream games from running Steam clients on your local network, effectively turning your gaming PC into a little render farm and allowing you to play from low-power devices like a laptop.

    With the help of OpenVPN, it's possible to enable playback of games from your home PC seamlessly while away from your home network too, provided you have a decent Internet connection. This tutorial will demonstrate how to setup an OpenVPN server on Fedora 23 with a bridged network connection in let you VPN into your home network and stream Steam games from PCs on your LAN.

    To make this work, we need to use OpenVPN in bridged mode with a tap network device. Bridging the ethernet and tap interfaces will allow VPN clients to receive an IP address on the LAN's subnet.

    The default (and simpler) tun devices are not bridged, and function on a separate subnet - something which will break in-home streaming. We need to be on the same LAN so that the UDP broadcast packets sent by Steam for auto-discovery will be received by the VPN clients.

    Creating a network bridge

    Let's start by setting up the network bridge with NetworkManager and enslaving the ethernet interface. Check the name of your active network interface by running nmcli d, and replace the value ofETH_IFACE with that name below:

    ETH_IFACE=enp3s0
    nmcli con add type bridge ifname br0
    nmcli c modify bridge-br0 bridge.stp no
    nmcli con add type bridge-slave ifname $ETH_IFACE master bridge-br0
    nmcli c up "bridge-slave-${ETH_IFACE}"
    nmcli c up bridge-br0

    Installing the OpenVPN server

    Next, in order to run an OpenVPN server, one needs to set up a certificate authority (CA) signs client certificates and authorizes them for login. In our case, we'll be using password authentication (for convenience) -- but OpenVPN still wants a CA setup and the server's certificate signed. Let's set up the CA for the OpenVPN server:

    dnf install easy-rsa
    cp -a /usr/share/easy-rsa/3 /root/openvpn-bridged-rsa
    cd /root/openvpn-bridged-rsa
    ./easyrsa init-pki
    ./easyrsa build-ca
    # Enter the CA password, then accept the defaults

    Now we need to create and sign the certificate for the server (set the value of SERVER_ALIAS to an alias of your choice):

    SERVER_ALIAS=homelab
    ./easyrsa gen-dh
    ./easyrsa gen-req $SERVER_ALIAS nopass
    ./easyrsa sign-req server $SERVER_ALIAS
    # Enter 'yes', then CA password

    Finally, we copy the keys and certificates to a dedicated folder for OpenVPN:

    mkdir /etc/openvpn/keys
    chmod 700 /etc/openvpn/keys
    cp pki/ca.crt pki/dh.pem "pki/issued/${SERVER_ALIAS}.crt" "pki/private/${SERVER_ALIAS}.key" /etc/openvpn/keys

    We are now ready to configure OpenVPN. Set the variables based on your LAN's configuration (see ifconfig $ETH_IFACE output if unsure):

    BRIDGE_IP=192.168.1.1
    NETMASK=255.255.255.0
    IP_POOL_START=192.168.1.241
    IP_POOL_END=192.168.1.254

    dnf install openvpn
    firewall-cmd --permanent --add-service openvpn
    firewall-cmd --reload

    cat << EOF > /etc/openvpn/bridged.conf
    port 1194
    dev tap0
    tls-server
    ca /etc/openvpn/keys/ca.crt
    cert /etc/openvpn/keys/$SERVER_ALIAS.crt
    key /etc/openvpn/keys/$SERVER_ALIAS.key # This file should be kept secret
    dh /etc/openvpn/keys/dh.pem
    server-bridge $BRIDGE_IP $NETMASK $IP_POOL_START $IP_POOL_END

    # Password authentication
    client-cert-not-required
    username-as-common-name
    plugin /usr/lib64/openvpn/plugins/openvpn-plugin-auth-pam.so openvpn

    # Allow multiple client connections from the same user
    duplicate-cn

    # Client should attempt reconnection on link failure.
    keepalive 10 120

    # The server doesn't need root privileges
    user openvpn
    group openvpn

    # Logging levels & prevent repeated messages
    verb 4
    mute 20
    log-append /var/log/openvpn.log
    status /var/log/openvpn-status.log

    # Set some other options
    comp-lzo
    persist-key
    persist-tun
    push persist-key
    push persist-tun

    # Brings up tap0 since NetworkManager won't do it automatically (yet?)
    script-security 2
    up up.sh
    EOF

    OpenVPN will create the tap0 interface automatically when the OpenVPN server starts. NetworkManager is able to enslave the interface to the bridge, but won't bring tap0 online. For that, we install a simple script:

    cat << EOF > /etc/openvpn/up.sh
    #!/bin/bash
    br=br0
    dev=\$1
    mtu=\$2
    link_mtu=\$3
    local_ip=\$4
    local_netmask=\$5

    # This should be done by NetworkManager... but it can't hurt.
    /sbin/brctl addif \$br \$dev

    # NetworkManager appears to be capable of enslaving tap0 to the bridge automatically, but won't bring up the interface.
    /sbin/ifconfig \$dev 0.0.0.0 promisc up
    EOF
    chmod +x /etc/openvpn/up.sh

    Next, we need to create the PAM authentication configuration file for the OpenVPN password plugin:

    cat << EOF > /etc/pam.d/openvpn
    #%PAM-1.0
    auth       substack     system-auth
    auth       include      postlogin
    auth       requisite    pam_succeed_if.so user ingroup openvpn_pw quiet
    account    required     pam_nologin.so
    account    include      system-auth
    password   include      system-auth
    EOF

    This configuration file requires that the users logging in be a member of the openvpn_pw group. You can adjust the file as you see fit.

    Finally open the OpenVPN port in the firewall and start the service:

    firewall-cmd --permanent --add-service openvpn
    firewall-cmd --reload
    systemctl enable openvpn@bridged
    systemctl start openvpn@bridged

    Configure the firewall

    By default, packets are filtered through iptables which can cause issues, as packets won't freely through between the interfaces. We can disable that behavior:

    cat << EOF > /etc/modules-load.d/bridge.conf
    br_netfilter
    EOF

    cat << EOF > /etc/sysctl.d/bridge.conf
    net.bridge.bridge-nf-call-ip6tables=0
    net.bridge.bridge-nf-call-iptables=0
    net.bridge.bridge-nf-call-arptables=0
    EOF
    sysctl -p /etc/sysctl.d/bridge.conf

    cat << EOF > /etc/udev/rules.d/99-bridge.rules
    ACTION=="add", SUBSYSTEM=="module", KERNEL=="br_netfilter", RUN+="/sbin/sysctl -p /etc/sysctl.d/bridge.conf"
    EOF

    Note that I assume that net.ipv4.ip_forward=1 (having libvirt seems to configure this automatically). If not, you'll want to tune the sysctl parameter net.ipv4.ip_forward to a value of 1.

    OpenVPN client configuration

    That's it! Send a copy of /etc/openvpn/keys/ca.crt on the server to your clients, and you should now be able to connect to your OpenVPN server using this very simple client configuration (don't forget to replace your.server.fqdn with your server's IP address or FQDN):

    client
    dev tap
    proto udp
    remote your.server.fqdn 1194
    resolv-retry infinite
    nobind
    persist-key
    persist-tun
    ca ca.crt
    auth-user-pass
    comp-lzo
    verb 3
    mute 20

    Once connected, you should be able to ping any machine on the LAN as well as fire up Stream for a remote gaming session.

    Appendix A: Steam on OS X

    Small note, if you're running the Steam client on OS X there's a bug where the client only sends its UDP broadcast packets for in-home streaming discovery on the machine's primary (i.e. Ethernet or Wi-FI) interface. This nifty command captures those and re-broadcasts them over the VPN's interface (once again, substitute the value of BROADCAST_ADDR per your LAN settings):

    BROADCAST_ADDR=192.168.1.255
    sudo tshark -T fields -e data -l 'udp and dst port 27036' | script -q /dev/null xxd -r -p | socat - UDP-DATAGRAM:${BROADCAST_ADDR}:27036,broadcast

    Special thanks to Larry Land for pointing that out in his blog post Run your own high-end cloud gaming service on EC2 (which is awesome and deserves a read, by the way).

    The above command requires the Wireshark and socat utilities to be installed, which you can grab using homebrew:

    brew install wireshark socat

    and if you don't know your subnet's broadcast address, verify it with:

    ifconfig tap0 | grep broadcast

    Appendix B: Troubleshooting tips

    Whenever possible, I like to use the most modern tooling available. This tends to bite me because documentation might not be as good or the feature set in the replacement tools might be lacking compared to the older tried and true tooling, but I try to always look forward. 'new' tooling like systemd, NetworkManager and firewalld might be rough around the edges, but I like modern feature set and consistency they bring. Most importantly, using them (instead of dropping various custom shell scripts here and there) feels a lot less like my server is held together with glue, which I like.

    While trying different configurations, I discovered a few tricks or debugging commands that proved very useful to me - particularly while migrating commands from online resources intended for the older tooling to the tools mentioned above. Hopefully, you'll find them useful too!

    It's always the firewall

    The blame for most of the issues you will experience generally fall under firewall or routing issues.

    First steps in testing should always be disabling the firewall (systemctl stop firewalld) and if that doesn't fix it, then move to checking the routes (route -n or netstat -rn).
    If you've identified the firewall is to blame, re-enable it and identifying the root cause by adjusting your configuration while listening for packets to see when packets start flowing again.

    Listening for packets

    This will be your most used tool. If things don't go as expected, listen on each of the tap0 (client), tap0 (server) and br0 (server) interfaces and then generate some traffic to see how far the packets:

    tcpdump -i IFNAME PATTERN

    where PATTERN can select for hosts, ports or traffic type. In this case, a particular favorite of mine was icmp or udp port 27036 as this let me test by trying to ping a machine on the LAN from the VPN client, as well as see if the Steam UDP traffic was making it in/out.

    Send UDP traffic

    The iperf utility can be used to test if UDP traffic makes it to the OpenVPN server (run iperf -c server.ip -u -T 32 -t 3 -i 1 -p 27036) from the OpenVPN clients/LAN machines (run iperf -s -u -i 1 -p 27036).

    Changing the zone of an interface

    firewalld has different 'zones', each with different rules (see firewall-cmd --list-all-zones). Interfaces will have the rules from the default zone applied to them unless otherwise configured, which you can do as follows:

    firewall-cmd --permanent --change-interface=IFNAME --zone=NEW_ZONE
    firewall-cmd --reload

    Adding raw IPTables rules to firewalld

    e.g. to accept all packet forwarding on the bridge interface:

    firewall-cmd --permanent --direct --add-rule ipv4 filter FORWARD 0 -i br0 -j ACCEPT

    or to allow all packets flowing over br0 and tap0:

    firewall-cmd --permanent --direct --add-rule ipv4 filter INPUT 0 -i tap0 -j ACCEPT
    firewall-cmd --permanent --direct --add-rule ipv4 filter INPUT 0 -i br0 -j ACCEPT

    Neither of these commands should be necessary given the netfilter sysctl parameters tweaked earlier, but certain OpenVPN options (such as client2client) change the packet flow and cause packets to flow over the interface, get filters, then re-injected which could cause them to suddenly be affected by the iptables rules.

    Recall that firewall-cmd --reload needs to be called before the permanent rules will take effect.

    Debugging IPTables

    The default iptables -L listing isn't very helpful when inserting/deleting rules by their chain offset. The following command lists all rules, numerically, and displays line numbers:

    iptables --line-numbers -L -n -v

    You can also log dropped packets for further troubleshooting (here limited to 1/s, inserted at position 15 which was the position before the DROP rules on my machine):

    iptables -I INPUT 15 -j LOG -m limit --limit 60/min --log-prefix "iptables dropped: " --log-level 4

    Configuring a client VPN connection using only NetworkManager

    VPN_IFNAME=homelab
    nmcli c add type vpn ifname $VPN_IFNAME vpn-type openvpn
    nmcli c modify $VPN_IFNAME
    set vpn.data dev = tap
    set vpn.data ca = /path/to/copy/of/ca.crt
    set vpn.data connection-type = password
    set vpn.data remote = your.server.fqdn
    set vpn.data comp-lzo = yes
    set vpn.data username = your_user
    set vpn.data connection-type = password
    set vpn.secrets password = your_pw

    'waiting for password' when connecting using Tunnelblock

    When I was attempting to test my VPN connections using Tunnelblick on OS X, I experienced an annoying bug: When trying to connect, Tunnelblick would enter a 'Waiting for password' state, but never 'get' the password nor prompt for one. Log were misleading:

    Tunnelblick: Obtained VPN username and password from the Keychain

    No VPN password was stored in my keychain (verified using Keychain Access.app). Fortunately, this post on the Sophos community forums correctly identified the issue as a bug after having copied/renamed a Tunnelblick connection.

    Tunnelblick's preference file needs to be adjusted in order to correctly prompt for a password again:

    # from https://community.sophos.com/products/xg-firewall/f/124/t/75819
    conname="homelab"
    defaults delete net.tunnelblick.tunnelblick "${conname}-keychainHasPrivateKey"
    defaults delete net.tunnelblick.tunnelblick "${conname}-keychainHasUsername"
    defaults delete net.tunnelblick.tunnelblick "${conname}-keychainHasUsernameAndPassword"

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