Seems that lo0, pflog0 and pfsync0 can be checked. I think I managed to debug some but not sure if it is useful.
$ gdb ifconfig GNU gdb (GDB) 7.6 (Debian 7.6-5) Copyright (C) 2013 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html > This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Type "show copying" and "show warranty" for details. This GDB was configured as "x86_64-kfreebsd-gnu". For bug reporting instructions, please see: <http://www.gnu.org/software/gdb/bugs/>... Reading symbols from /sbin/ifconfig...(no debugging symbols found)...done. (gdb) run lo0 Starting program: /sbin/ifconfig lo0 lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> metric 0 mtu 16384 options=600003<RXCSUM,TXCSUM,RXCSUM_IPV6,TXCSUM_IPV6> inet6 fe80::1%lo0 prefixlen 64 scopeid 0x6 inet 127.0.0.1 netmask 0xff000000 inet6 ::1 prefixlen 64 nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL> [Inferior 1 (process 18483) exited normally] (gdb) run nfe0 Starting program: /sbin/ifconfig nfe0 nfe0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500 options=82008<VLAN_MTU,WOL_MAGIC,LINKSTATE> Program received signal SIGSEGV, Segmentation fault. 0x00000008010c88ec in _IO_vfprintf_internal (s=<optimized out>, format=<optimized out>, ap=ap@entry=0x7fffffffd148) at vfprintf.c:1649 1649 vfprintf.c: No such file or directory. (gdb) run vlan20 The program being debugged has been started already. Start it from the beginning? (y or n) y Starting program: /sbin/ifconfig vlan20 vlan20: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500 Program received signal SIGSEGV, Segmentation fault. 0x00000008010c88ec in _IO_vfprintf_internal (s=<optimized out>, format=<optimized out>, ap=ap@entry=0x7fffffffd148) at vfprintf.c:1649 1649 vfprintf.c: No such file or directory. (gdb)
