One IP used on more than one interface (gif0 and lo0)

[Charlie ROOT]

I was asking because of this:

"To make firewalling and managing traffic f lowing thru the ip tunnel
 a little easier I used virtual interfaces; I added aliases to the
 loopback interface(lo0) on both gateways to use as inside endpoints
 for the tunnel. That way I have a chance to control the traffic at the
 gateway before passing it on out the internal interface to it's local
 network. Useful for NAT situations, trouble-shooting and easier to setup
 firewall rules because it is easier to picture/diagram the network flow."

                "IPsec VPN using FreeBSD"
                 Greg Panula, 2001
                 GSEC Practical version 1.2e
                 / www.sans.org/rr/papers/21/795.pdf /


 "
  ...

  First setup the aliases
  On bert I added 5.5.5.1 as the alias

  ifconfig lo0 alias 5.5.5.1 netmask 255.255.255.252

  ...

  Next actually setup the tunnel
  On bert I did this:

  gifconfig gif0 2.2.2.2 3.3.3.3

  ifconfig gif0 inet 5.5.5.1 5.5.5.2 netmask 255.255.255.252 "


  Can somebody picture/diagram me the network flow..
  The incoming packets - what exactly happens with them?
  From which interface they came from - gif0? And if they
  did - what is the alias on lo0 for?


 Best regards,
 Fro