{"id":5593,"date":"2023-10-02T21:03:44","date_gmt":"2023-10-03T05:03:44","guid":{"rendered":"https:\/\/wonghoi.humgar.com\/blog\/?p=5593"},"modified":"2023-10-21T00:28:28","modified_gmt":"2023-10-21T08:28:28","slug":"installing-softether-vpn-server-in-asus-merlin-wrt","status":"publish","type":"post","link":"https:\/\/wonghoi.humgar.com\/blog\/2023\/10\/02\/installing-softether-vpn-server-in-asus-merlin-wrt\/","title":{"rendered":"Installing SoftEther VPN Server in Asus Merlin WRT"},"content":{"rendered":"\n
I’m experimenting with SoftEther as the user experience\/interface is a lot more polished than WireGuard and OpenVPN and it has wide platform coverages. The Windows administration interfaces are sensibly designed (organized conceptually), unlike the Linux software culture that basically pretend to have a user interface yet it’s just a step away from editing the raw config file. SoftEther’s documentation also has nice graphical illustrations and it’s use cases oriented. The best part of the docs is that they are short and to the point. <\/p>\n\n\n\n
Here I have a use case that’s not as quite as common for SoftEther’s users, so I might as well do a quick write up so if I run into this again in the future, I don’t have to do the research again.<\/p>\n\n\n\n
Use case: router doubling as VPN server<\/h2>\n\n\n\n
I made a diagram based on my current understanding of how ethernet router works, and what needs to be done to have the router dual as SoftEther VPN server. <\/p>\n\n\n\n
No guarantee that it’s the correct model and the lingo, and I’d appreciate comments to help me improve as I’m still learning (I was in algorithms and non-networking software development, more on the DSP side + light embedded systems, so this area is new to me).<\/p>\n\n\n\n
<\/p>\n\n\n\n
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The part shaded in blue is the new part we are building. <\/li>\n\n\n\n
Installing SoftEther from Entware is just the square block. <\/li>\n\n\n\n
You need to modprobe tun<\/code> to let<\/span><\/strong> the SoftEther Server Admin software create the TAP port (made up Ethernet card).<\/li>\n\n\n\n
At the same time the TAP port is created, say tap0<\/code>, what SoftEther ‘bridges<\/em>‘ is NOT the LAN, but the orange<\/mark> link in the diagram that goes to the virtual hub (which belongs to a VPN server instance). This lingo confusion wasted me days.<\/li>\n\n\n\n
The ‘bridge’ on SoftEther’s side tells the incoming VPN connection which ‘Ethernet card’ (turns out to the the TAP interface) on the host computer should act on its behalf. <\/li>\n\n\n\n
I felt like something is odd that SoftEther did not ask me what local network should the TAP interface go into so I suspect the TAP is just sitting there not talking to anybody, and it turned out to be the reason why my incoming VPN connection succeed but I’m not getting DHCP assignments.<\/li>\n\n\n\n
I bit the bullet and understand how a Linux router work as if it were a computer with 5 Ethernet cards and one important piece of the puzzle is that the 4 LAN ports aren’t directly talking to the the WAN, but instead they form a bridge (software switch) which the bridge represents them and talk to the processed WAN traffic.<\/li>\n\n\n\n
So the missing link is the double-line on the diagram where I add the TAP interface to the LAN bridge, namely brctl addif br0 tap_tap0<\/code>. Linux adds a tap_<\/code> prefix to tap interfaces so it’s tap_tap0<\/code> for tap0<\/code> in SoftEther.<\/li>\n\n\n\n
One more non-obvious thing here is that you also need to register the brctl<\/code> a few seconds (using sleep<\/code> delay) right after the SoftEther VPN Server service starts and nowhere else. The TAP has to exist before you put it on the LAN bridge and the TAP is programmed correctly to be as short-lived as needed, which is very responsible.<\/li>\n<\/ul>\n\n\n\n
What to watch out for this use case<\/h2>\n\n\n\n
SoftEther’s interface does support creating a TAP adapter, but it provides scary warnings as this is an unusual settings. <\/p>\n\n\n\n
TAP depends on the TUN module being loaded first, but Merlin-WRT’s firmware do not load this out of the box. <\/p>\n\n\n\n
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