Marco wrote a useful post yesterday about some less widely known features of iproute.
I didn't know about the dummy interface:
ip link add mydummy type dummy
but I've definitely used the tun/tap driver before. I always forget the syntax so I'll jot it here for reference:
ip tuntap add dev mytap mode tap user albertlash
Also mentioned is one of my all-time favorite iproute features: GRE tunnels!
ip link add blah type gretap remote 192.168.8.1 ip link add barf type gretap help
I'm thrilled that pfsense will soon include GRE tunneling support!