Usage

ifconfig is a utilty can used for getting information about network interfaces and stack, chagning them or adding virtual interfaces.

running ifconfig without any options will show usually something like this:

lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 32768
        index 3 priority 0 llprio 3
        groups: lo
        inet6 ::1 prefixlen 128
        inet6 fe80::1%lo0 prefixlen 64 scopeid 0x3
        inet 127.0.0.1 netmask 0xff000000
em0: flags=8b43<UP,BROADCAST,RUNNING,PROMISC,ALLMULTI,SIMPLEX,MULTICAST> mtu 1500
        lladdr aa:bb:cc:dd:ee:ff
        index 1 priority 0 llprio 3
        groups: egress
        media: Ethernet autoselect
        status: active
        inet 12.34.56.78 netmask 0xffffff00 broadcast 12.34.56.78
        inet6 2002::ffff:ccff:fedd:ee06%vio0 prefixlen 64 scopeid 0x1
        inet6 2002:ffff:2:1040:: prefixlen 48
enc0: flags=0<>
        index 2 priority 0 llprio 3
        groups: enc
        status: active
pflog0: flags=141<UP,RUNNING,PROMISC> mtu 33136
        index 4 priority 0 llprio 3
        groups: pflo

besides em0, all other interfaces mentioned (pflog0, enc0, lo0) are virtual and they will exist on all openbsd installations most of times.

em0: flags=8b43<UP,BROADCAST,RUNNING,PROMISC,ALLMULTI,SIMPLEX,MULTICAST> mtu 1500

it shows em0's mtu (maximum size of a packet) and flags set on it. some can changed using software, some are hardware-dependent and can't without changing hardware.

lladdr aa:bb:cc:dd:ee:ff

this refer about MAC adderss used by this interface, which is aa:bb:cc:dd:ee:ff

inet 12.34.56.78 netmask 0xffffff00 broadcast 12.34.56.78

this is referring to ip address, netmask and broadcast address ip address can be local, if you are using NAT

inet6 2002:ffff:2:1040:: prefixlen 48

inet6 is like inet but for ipv6.