Linking interfaces and system variables

[Dambielle Yannick]

Hello everybody,
I have 2 questions.
Firslty, is there a way to "link" interfaces by using some system variables
like the one I can use for bridging interfaces  ? i.e. sysctl
net.link.ether.bridge_cfg=rl0,rl1.
Then, according to the freebsd handbook it exist almost 500 system variables
which can be read and set. Does it exist a paper or anything else that
explain all that variables and why they are used ?
best regards,
Yannick