Discover IP & mac addresses of most devices on your network

discover_ips.sh

# First, find your broadcast address
#
ifconfig

# - Should return something like the below, where 192.168.1.255 is
# - the broadcast address
# -
# - eth0      Link encap:Ethernet  HWaddr b8:27:eb:19:c6:01  
# -           inet addr:192.168.1.109  Bcast:192.168.1.255  Mask:255.255.255.0
# -           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
# -           RX packets:1436 errors:0 dropped:0 overruns:0 frame:0
# -           TX packets:367 errors:0 dropped:0 overruns:0 carrier:0
# -           collisions:0 txqueuelen:1000 
# -           RX bytes:136126 (132.9 KiB)  TX bytes:45970 (44.8 KiB)
 -
# - lo        Link encap:Local Loopback  
# -           inet addr:127.0.0.1  Mask:255.0.0.0
# -           UP LOOPBACK RUNNING  MTU:16436  Metric:1
# -           RX packets:0 errors:0 dropped:0 overruns:0 frame:0
# -           TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
# -           collisions:0 txqueuelen:0 
# -           RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)


# Ping the broadcast address
#
ping -b 192.168.1.255  # quit with control-C after a little bit

# - WARNING: pinging broadcast address
# - PING 192.168.1.255 (192.168.1.255) 56(84) bytes of data.
# - 64 bytes from 192.168.1.1: icmp_req=1 ttl=255 time=0.912 ms
# - 64 bytes from 192.168.1.4: icmp_req=1 ttl=64 time=1.35 ms (DUP!)
# - 64 bytes from 192.168.1.102: icmp_req=1 ttl=64 time=1.36 ms (DUP!)
# - 64 bytes from 192.168.1.105: icmp_req=1 ttl=64 time=117 ms (DUP!)
# - 64 bytes from 192.168.1.104: icmp_req=1 ttl=64 time=125 ms (DUP!)
# - 64 bytes from 192.168.1.100: icmp_req=1 ttl=64 time=160 ms (DUP!)
# ^C


# Now your ARP cache will have the IP and mac addresess of any machines
# that respond to broadcast pings.  (Apparently windows machines don't
# by default.)
#
# List those out.
arp -a

# - Outputs something like
# - ? (192.168.1.1) at 0:1f:f3:c7:52:f4 on en0 [ethernet]
# - ? (192.168.1.4) at d4:9a:20:c2:bc:a4 on en0 [ethernet]
# - ? (192.168.1.100) at 68:9:27:62:a4:73 on en0 [ethernet]
# - ? (192.168.1.102) at 58:b0:35:fd:b8:7 on en0 [ethernet]
# - ? (192.168.1.104) at f8:1e:df:be:c9:d2 on en0 [ethernet]
# - ? (192.168.1.105) at 60:33:4b:16:8a:69 on en0 [ethernet]
# - ? (192.168.1.109) at b8:27:eb:19:c6:1 on en0 [ethernet]
# - ? (192.168.1.255) at ff:ff:ff:ff:ff:ff on en0 [ethernet]