ipv4 is net-pf-2...
some other networking protocol families..
# alias net-pf-1 off # Unix
# alias net-pf-2 off # IPv4
# alias net-pf-3 off # Amateur Radio AX.25
# alias net-pf-4 off # IPX
# alias net-pf-5 off # DDP / appletalk
# alias net-pf-6 off # Amateur Radio NET/ROM
# alias net-pf-9 off # X.25
# alias net-pf-10 off # IPv6
# alias net-pf-11 off # ROSE / Amateur Radio X.25 PLP
# alias net-pf-19 off # Acorn Econet
Hope it helps..