Hello,

On 4/11/2018 9:20 PM, Etienne Dechamps wrote:

No, the "via" option doesn't have any effect, because it only has effect at layer 2, e.g. on an Ethernet network. tinc running in router mode is a layer 3 (IP) network, not a layer 2 (Ethernet) network.

When you use that option on a layer 2 network such as Ethernet, the "via" option determines which layer 2 host (i.e. which MAC address, after ARP resolution) the packet will go to. In "router mode" tinc there are no MAC addresses, and tinc decides where to send packets based on destination IP address, not the kernel.

Thank you for that info. I did not realize the part about the MAC address when using system/kernel routing. That makes a lot of sense. It explains other issues I had in the past with (for me) unexpected behaviour of tinc.

    So is there a way to send packets to a specific gateway ip using
    ip route?


If you change the tinc mode to "switch", then your tinc VPN will behave just like a physical Ethernet network, and the "via" option will work just like it does on a real network. But note that setting that option comes with a long list of consequences and is quite a radical, breaking change. (Also keep in mind that all nodes on your network need to use the same mode.)

No. I really do not want to use tinc in switch mode.

An alternative solution to your problem, besides going one layer down, would be to go one layer up: you could set up a "tunnel within the tunnel", i.e. hosta could establish a tunnel to hostc *on top of* the tinc VPN. Then, if you want certain packets to go through hostc, you can just send them through that tunnel and you're done. I am actually using such a solution for a special purpose on my own tinc network right now. The simplest solution for the tunnel is to use IP/IP, which has minimal overhead and is easy to understand and troubleshoot. I contributed some code to tinc that provides better support for that use case: https://github.com/gsliepen/tinc/pull/166 <https://github.com/gsliepen/tinc/pull/166>
Thanks for that suggestion.

I am using the ip/ip tunnel over tinc construction now and it works like a charm. Very easy to implement too.

Thank you all for helping me out and making me understand tinc a little better.

Regards

Hans








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