Wednesday, August 3, 2016

Musings on bringing up services on freebsd-wifi MIPS devices, or "why cross compiling is important"

FreeBSD has run on these MIPS routers for quite some time, but it was limited to what ships in base. There's not been any cross-built packages as part of the image building, which means we can't easily have third-party functionality.

Now, some of this third-party functionality is pretty important these days. Relying on telnet sucks; I'd like to have dropbear as an SSH server so we at least have SSH. Not having a DNS relay or DHCP server also sucks; dnsmasq would solve this problem. I'd also like some VPN services, so openvpn would be nice.

So, I eventually snapped a few months ago and started integrating some external toolchain compiler use with the freebsd-wifi-build scripts. bapt@freebsd did a whole lot of work to build ports of cross-compilers to be used by the FreeBSD ports and base system so I'm leveraging that for doing MIPS cross compiling. A bit of hacking later, and I'm cross compiling dnsmasq, dropbear, openvpn and lua.

Then I needed to integrate things. I wrote up a bunch of simple startup script wrappers to generate suitable config files for these services. Everything except the openvpn server/client configuration is in the rc.conf file, which will eventually make it much easier to turn into a configuration database.

OpenVPN was the most amusing. It cross compiled fine, save needing liblzo for compression (so that's disabled for now.) However, FreeBSD's openvpn package is version 2.3 but the easyrsa component is actually from 3.0 - which means all the documentation is out of date.

I used this for the OpenVPN config:

And this for easyvpn:

And digitalocean have a writeup for how to convert the config file into a combined config file and certification bundle:

A few things tripped me up:
  • as mentioned before - the lack of freebsd openvpn documentation that works with easyvpn 3.0 made things frustrating;
  • openvpn really wants valid system time, so I am going to have to run ntpdate when the WAN comes up;
  • there's no RTC on many of these router boards, making time keeping very much reliant on NTP;
  • kernel NAT works pretty well, but it needs interfaces to be up before you can add them. I'll have to add some scripts to openvpn-client to setup the NAT state once the link comes up so this stops being a problem;
I'll go into a little more detail about the details in a future post. But, hi from being behind an openvpn-client LAN gateway!

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