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Is there a way to use a vpn on one network card, and use a second network card for a regular connection? (lemmy.dbzer0.com)
submitted 4 weeks ago by Tippon@lemmy.dbzer0.com to c/linux@lemmy.ml
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I've got a Linux server running Xubuntu at the moment (It was a media player first), and it also runs two Minecraft servers for the family. It has two network cards that are both connected to the internet. Is there a way to bind the VPN to one of the cards and use the other one for regular use?

I've got Surfshark as my VPN, and it doesn't allow port forwarding under Linux. I've got some software that I want to keep behind the VPN, but the lack of port forwarding is stopping me from sharing the Minecraft servers, and when the VPN is active, it slows down the connection to some of my services like Plex.

I've tried to look it up, but I just don't know enough to get myself anywhere. I've found results that talk about name spaces and routing tables, but they assume a level of knowledge that I just haven't got yet.

I want to use the Arr suite and qBittorrent as the main programs behind the VPN, and Plex, Mylar (a comic manager), Syncthing, and Minecraft as the main programs without it. If I set up qBittorrent and the Arrs as Docker containers, can I use Gluetun to bind just them to the VPN? The VPN is using OpenVPN connections if that makes a difference.

Thanks in advance :)

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[–] lungdart@lemmy.ca 41 points 4 weeks ago* (last edited 4 weeks ago) (4 children)

Yes that's called routing.

You don't bind it to a NIC, you specify the destinations you want forwarded to each interface. Your VPN connection is just another interface.

If you're looking for good docs, you may want to Google split tunnel vpn, and also bone up on your networking.

A few static routes should get you what you need

[–] Mihies@programming.dev 9 points 4 weeks ago (2 children)

And one doesn't even need two NICs, right.

[–] lungdart@lemmy.ca 4 points 3 weeks ago

One NIC is fine

[–] ReversalHatchery@beehaw.org 1 points 3 weeks ago

yeah, VLAN interfaces and other kinds of virtual interfaces can also be used. I think you can even have multiple "sub interfaces", that will receive distinct IPs from the local DHCP server

[–] jet@hackertalks.com 3 points 3 weeks ago* (last edited 3 weeks ago) (2 children)

Everything you said is true, but I don't think it's the complete answer the OP would like.

For instance if somebody goes to Google, on the raw network, and on the VPN. They would correctly expect that traffic to take two different routes, and come from different IP addresses Even if the destination target IP address is the same

[–] lungdart@lemmy.ca 3 points 3 weeks ago

goes to Google, on the raw network, and on the VPN.

You can't "go" to a destination on two networks in a single request. It's all packets on a wire, if it comes from two sources, it was two requests.

Unless you mean two different requests. As in while on the VPN everything is tunneled, and while not on the VPN it's not, but this is the opposite of what the OP was asking for. He wants the VPN on for some use cases, and off for others. That's split tunneling.

He'll likely wind up with difficulties around trying to figure out which destinations he doesn't want routed through the VPN, because there's no way to do it by protocol, since routing happens on layer 3, not 4 or 7. He'll likely need to know those address in advance.

[–] mvirts@lemmy.world 2 points 3 weeks ago

I think the key to this idea is that as long as the VPN only apps are running in docker containers, container networking can be used to restrict their traffic to the vpn.

Apps like qBittorrent support proxy connection options for this scenario without containers.

https://github.com/qbittorrent/qBittorrent/wiki/Explanation-of-Options-in-qBittorrent#proxy-server

[–] Tippon@lemmy.dbzer0.com 1 points 3 weeks ago (1 children)

Apologies for the slow reply :)

These are the things that I don't understand. When you say I need to specify the destinations, does that mean the destination of the traffic, like lemmy.dbzer0.com, or the destination network interface like tun0 or enp2s0?

I'm searching for split tunnel VPN, but the majority of results are either sales sites, or Stack Overflow with no confirmed answers.

I've been having a bit more luck with this page after searching for Jet's answer below:

https://manpages.ubuntu.com/manpages/trusty/man8/ip-netns.8.html

but I'm still confused >.<

[–] lungdart@lemmy.ca 2 points 3 weeks ago

Routing takes place on layer 3 (ip) so destinations are ip networks and hosts.

Each packet you create has a destination IP. Your computer looks at your route table to see where it goes by matching the destination ip with each network. It will be sent to the most specific match first and your default gateway last.

If you're default gateway is you're vpn server via your vpn interface then you just need to add more specific route for destinations of interest through a different gateway (you're router) via the physical interface