The Switch To Mac

Why Do I Need To Know My IP Address?
If you’re doing home networking, you may need to know your IP address. For e.g.
if you want to exchange files between your Mac and windows PCs, you will need to
know your Mac IP address. It’s good to know the command to find out your
IP address. This post is about using the ifconfig Terminal command.
If you are familiar with the windows command ipconfig, the Terminal ifconfig is very similar.

Where Is ifconfig?
To bring up ifconfig, click on Finder – Applications – Utilities – Terminal. The Terminal window will
appear. At the prompt type in ifconfig and hit Enter. You will see something like this:

lo0: flags=8049 mtu 16384
	inet6 ::1 prefixlen 128
	inet6 fe80::1%lo0 prefixlen 64 scopeid 0x1
	inet 127.0.0.1 netmask 0xff000000
gif0: flags=8010 mtu 1280
stf0: flags=0<> mtu 1280
en0: flags=8863 mtu 1500
	ether 00:25:4b:bb:ad:d8
	media: autoselect
	status: inactive
en1: flags=8863 mtu 1500
	ether 00:25:00:46:ff:5b
	inet6 fe80::225:ff:fe46:ff5b%en1 prefixlen 64 scopeid 0x5
	inet 192.168.1.6 netmask 0xffffff00 broadcast 192.168.1.255
	media: 
	status: active
fw0: flags=8863 mtu 4078
	lladdr 00:25:4b:ff:fe:bb:ad:d8
	media: autoselect 
	status: inactive
vnic0: flags=8843 mtu 1500
	ether 00:1c:42:00:00:08
	inet 10.211.55.2 netmask 0xffffff00 broadcast 10.211.55.255
	media: autoselect
	status: active
vnic1: flags=8843 mtu 1500
	ether 00:1c:42:00:00:09
	inet 10.37.129.2 netmask 0xffffff00 broadcast 10.37.129.255
	media: autoselect
	status: active

ifconfig Format
The leftmost column displays device names followed by a colon. The ones we’re interested in
are the ones that have a status of “active” where I have boldfaced the active
sessions for my Mac. Where you see the line that begins with inet, the ip address is right next
to it. For this Mac, there are three ip addresses that can address it: 192.168.1.6, 10.211.55.2
and 10.37.129.2

Device Names
There *is* some rhyme or reason to the device names. The en0 device is for the wired ethernet
connection on my Mac. At the moment it is not being used and hence its status is inactive.
The en1 device refers to my Air Port (wireless) connection. The vnic0 device is a virtual
network interface card zero; the vnic1 device is a second virtual interface. The lo0 device is
testing the loopback, the default “address” used to test the ip configuration of a workstation.
The fw0 device refers to the firewire interface. I’m not sure what the gif0 and stf0 are for; these could
be “addressed” in a future post. No pun intended : ).  Any of the active
ip addresses will work when addressing my Mac, but I would consider the en0 device the main
ip address since it is assigned to the Air Port.

IP Address Defined
The simplest definition that I can think of for an ip address is that it is similar to a house address.
When two devices are communicating with each other,  each needs to know the other’s address to find
it. Each address is a series of four octets separated by periods. ww.xx.yy.xx   Each octet ranges from
0 to 255. The address that your workstation is assigned is dependent upon the “network” that it’s in.
For most  home router networks, they usually begin with 192 dot something. This is only used for home networks.
If you have a static ip address from your internet provider, it will most likely be some other number
combination.

Every device on the internet has to have an ip address. Even places like google and yahoo have
addresses. How do you find their address? You can go to Terminal and do a ping of the url.
For e.g. ping www.google.com; then hit control-z to stop sending bytes.

TomsMacBookPro:~ Tom$ ping www.google.com
PING www.l.google.com (74.125.95.147): 56 data bytes
64 bytes from 74.125.95.147: icmp_seq=0 ttl=53 time=26.834 ms
64 bytes from 74.125.95.147: icmp_seq=1 ttl=53 time=24.630 ms
64 bytes from 74.125.95.147: icmp_seq=2 ttl=53 time=25.069 ms
64 bytes from 74.125.95.147: icmp_seq=3 ttl=53 time=25.810 ms
64 bytes from 74.125.95.147: icmp_seq=4 ttl=53 time=35.377 ms
^Z
[4]+  Stopped                 ping www.google.com
TomsMacBookPro:~ Tom$

To test the ip address, if you bring up your browser and type in
http://74.125.95.147  google should come up.

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