Out there, in the vast space of Internet, there is a good presentation about network stack virtualization in OpenBSD, presented in 2009 by Claudio Jeker at Slackathon;
Schizophrenic Firewalls - virtualized network stack and other crazyness in OpenBSD:
https://www.youtube.com/watch?v=NfyyBI7JHQI - as usual, youtube-dl is good choice to preserve it. Slides:
http://www.openbsd.org/papers/f2k9-vrf/
And the article written also by C. Jeker in 2008,
OpenBSD network stack internals: http://www.openbsd.org/papers/asiabsdcon08-network.pdf that is related to VRF (virtual routing and forwarding) and Label Distribution Protocol, which distributes MPLS label mappings between routers <-- and to MPLS I found also text written by him;
Demystifying MPLS The MPLS framework in OpenBSD:
https://2011.eurobsdcon.org/papers/jeker/MPLS.pdf