Makes It Easy to Share Your Mac's Screen Locally and Over the Internet
by Alan Zisman (c)
published in Low
June 30, 2008: ZisMac column
ability to view and optionally control the screen of a remote computer
can be very handy in a number of scenarios. Maybe you have a parent
living in another city with questions about their computer or problems.
Trying to help someone over the phone can be problematic, if when you
say "Open the Finder" they reply, "What's the Finder"?
It's much easier to open a window to their Mac, open the Finder, and
show them what you mean.
I'm at work, sitting at a Windows XP computer, and realize I really
need to read a file that's sitting on the hard drive of the iMac on my
desk at home. Again, it could be very convenient to have the power to
open a window to my home Mac from work.
One of Leopard's
improved features that's easy to miss is screen sharing; Mac OS X 10.4
had a built-in screen-sharing host, built on the open source VNC
but failed to include a VNC client. As a result, users could use the
Networking system preference to turn on screen sharing but couldn't
remotely access their shared screen without getting a third party
utility, like the free Chicken
of the VNC
adds the missing link - in fact, they include two different ways to
connect to a shared screen; each has its advantages, but neither is
Turn on screen sharing
order to connect to a remote Mac, screen sharing first needs to be
enabled on that Mac. That's done in the Sharing system preference:
that it's easy to turn screen sharing on; when you do that, you're told
how to connect to your Mac . . . take note - but also note that this
information may not be universally usable. For instance, you can only
use the information in the screen shot to connect to my 12" PowerBook
if you happen to be connected to my local network - which none of you
are. You can optionally control who is able to make use of this screen
There's an optional Computer Settings button; clicking it gives the
Not Very Remote:
Connecting Across a Local Network
got two Macs at home; I've enabled screen sharing on both. So I can sit
with my PowerBook on my lap and open a window to the iMac in my home
office, enabling me to run applications (like Quicken) that are only on
the iMac. To do that from the PowerBook, I click on the Finder's Go
menu and choose Connect to Server, the last item on the menu. Just as
it said in the Sharing system preference pane, I type in vnc://
followed by the IP address of that Mac.
you're going to do that more than once, you may want to click on the
[+] button to add that address to the favourites list in the bottom
half of the dialogue box.)
Click Connect, and pretty quickly a
window to the remote Mac opens up. My 17" iMac defaults to a 1440 x 900
display, while my 12" PowerBook has a 1024 x 768 screen. Nicely, the
Screen Sharing application scales the larger iMac display so that it
all fits on my smaller PowerBook screen. Very nicely done.
thing to be aware of, though. My various computers at home are
connected to a router and get their IP addresses via the default DHCP
networking option; that means that their IP addresses are temporary,
assigned by the router, and could change. In reality, I've found that
the DHCP-generated IP addresses are pretty stable, but if you're unable
to connect, you may need to walk over to the other computer and check
its IP address.
Perhaps easier than having to know the IP
address of the remote computer on you local network: Once you've
enabled screen sharing in this way, clicking on the computer in the
Finder's sidebar, you'll now see an option to share its screen - just
pick that (and optionally enter log in information), and away you go.
Alternatively, clicking the Browse button in the Finder's Go/Connect to
Server dialogue will take you to the same place. Either way, there's no
typing IP addresses required.
may notice that my screen shot shows that when I'm connected, I'm
running a program named Screen Sharing. You won't find a program with
that name in your Mac's Applications or Applications/Utilities folders.
Instead, it's cleverly buried away in the System/Library/CoreServices
folder, along with the Finder application and a number of other basic
Connecting Across the Internet
this works fine as long as I'm connected to the same local area network
as my not-very-remote other Mac. It's nice to be able to open an
application on the other Mac without have to get out of my comfortable
easy chair, but frankly, I probably could walk across the house without
too much difficulty.
More useful is the ability to contact my
iMac from a real 'remote' location - from work, for example, or when
traveling. That can be done, but it requires a bit more work. The thing
is that those 192.168.xxx.xxx IP addresses are for local area networks;
the designers of the Internet and TCP/IP networking set them (and
several other blocks of addresses) aside for private local networking
use, making them inaccessible across the Internet. This is a very good
thing, allowing a computer on your home or office network and a
computer on my home network to both have the same IP address without
conflicting with one another. The router has an IP address that is
connected to the rest of the world. All the computers (and other
devices) connected to that router share that single connection. This
minimizes the number of IP addresses in use - also a good thing, as IP
addresses are in increasingly short supply. And having the router in
between your computers and the Internet is also a good thing, providing
a layer of protection - outsiders wanting to access your computer first
have to get past the router and generally fail to do so.
legitimately want to access your computer from outside. To do that, you
need to modify your router's settings to allow for screen sharing.
popular routers can be accessed using a web browser and pointing to the
router's address on your network; you'll be asked for login information
and then directed to a webpage built right into the router. (If you
don't know the default IP address and the login information, check the
documentation that came with your router, either in print or on a CD;
if you've lost that, it's generally available online at your router
Exact details of what to do next vary
from router to router. Here's what works with my D-Link wireless
router. On my router, going to http://192.168.0.1 gets the following
changed the default log-in password (and suggest you do the same!),
though I kept the default user name of 'admin'. Once I'm logged in,
there's a screen offering a Wizard or Manual Configuration. The Wizard
won't give the advanced options I need; pick the Manual Configuration.
the initial Manual Configuration screen doesn't have what I want - port
forwarding. Clicking the Advanced button along the top got me there:
may notice that I'd already set port forwarding to allow me to access
my Slingbox device so that I can remotely view my cable TV.
probably don't have a Slingbox. To enable screen sharing, however, I've
added port forwarding for two ports: 3283 and 5900, setting them to
forward an application named Apple Remote Desktop (the name doesn't
really matter - this is just a convenience for the user so they will
know what it is when checking here later) to the IP address of my iMac
- the computer whose screen I want to share.
Note at the
right-hand side of the window, there's a field for 'Traffic Type'; I've
selected TCP. As well, further down, in a part of the window not
visible in the screen shot, I've repeated those same ports application
name, and IP address, this time setting Traffic Type to UDP. (There's
also a potential setting of 'Any' - that might have let me avoid the
duplication. Feel free to experiment.)
After making those
changes, I logged out, saving my changes. That should have applied the
saved changes to my router, but just to be sure, I reset it by pulling
out the power cable, plugging it back in, and waiting a few moments to
let it reconnect to the Internet.
But we're still
not ready - we need to know what IP address your home network gets from
your Internet Service Provider. That's the address you'll need to
connect to in order to access your Mac's screen remotely.
One way to find that out is to open your browser (assuming you're at
home, within your network) and point to: www.whatismyip.com
. That will
quickly report the IP address you're using to connect.
couldn't use that IP to address to connect to my iMac from my PowerBook
when both were connected to my home network. But when I took my
PowerBook to work and typed that address in using the Finder's
Go/Connect to Server menu, it worked just fine. It's a bit slower than
connecting at home, but quite usable.
I've tried it from other remote sites, and it's worked without problem.
But it gets better.
Windows, too, Can Share
Your Mac's Screen
work, I've got a Windows XP system on my desk. Windows does not include
VNC screen sharing as a built-in feature (though Microsoft includes its
own proprietary screen sharing for remote access). But because VNC is
an open-source protocol, there are a variety of utilities available for
download and installation on Windows systems. I've got TightVNC
installed - I use it in my school's computer lab to see what students
are doing on their computers out of my sight, and to access my school's
servers for administration.
Typing my home network's IP address
into TightVNC and entering my password opens my home iMac in a window
on my XP system at work. It's got more configuration options to fiddle
with, though the default settings worked okay for me.
updates are slower in my tests than Mac to Mac using Leopard's Screen
Sharing - though it may be that fiddling with the TightVNC options
could improve this. Nevertheless, it's usable and will prove to be
useful from time to time. (Below you can see me starting to edit this
article on my iMac - in a window on my Windows Vista laptop.)
But How Can I Use This
with My Mom?
can't imagine getting my mom to set up port forwarding on her router,
even with me on the phone. I would need to have screen sharing up and
running in order to try to do this for her. And since I want to be able
to share screens with her in order to help with her computer, that's
not going to be much help.
But Apple has added another screen
sharing feature to Leopard. This one isn't much use when I'm trying to
get at my home computer from work, but it's pretty much perfect for
using one Mac to share the screen of another Mac when both users are
sitting at their Macs.
It uses iChat. (And you thought that iChat was just for chat!)
In order to make use of iChat screen sharing, a number of things need
to be in place:
- Both users need to have accounts that work with
iChat. These could be .mac accounts, AOL Instant Messenger accounts, or Google Talk
accounts. (Unlike .mac, AIM and Google Talk accounts are free. Google
Talk uses the open source Jabber protocol - it's possible that other
Jabber-based accounts may work as well.)
- Users should be on each others' Buddy lists within
users need to have OS X 10.5 Leopard installed on their Macs; this is a
Leopard-to-Leopard feature, unlike the screen sharing described above,
which can connect any computers (Mac, Windows, whatever) with a
VNC-compatible protocol in place.
- Users need to enable screen
sharing - both in the Sharing system preference (as described above)
and in iChat; in iChat's Video menu (or the Audio menu on my
camera-less PowerBook), just click the Screen Sharing Enabled menu item.
all these are true, both users just need to open iChat. Either should
start a chat with the other. At the bottom of the little window showing
buddies there is a series of icons- for text chatting, audio chatting,
video chatting, and last an icon with an overlapping pair of rectangles
for screen sharing.
on it let's you choose to ask the person with whom you're chatting to
either let you share his/her screen or to agree to share your screen.
Pick one, and they'll see something like this:
the other person clicks on the message to agree to it, you'll see large
text pop up on your screen noting that this person is now sharing your
screen. (This disappeared too quickly for me to be able to capture the
If you're sharing another user's screen, you can will see
their screen in a large window (and share control of their mouse and
keyboard) and see your screen in a small window. Clicking in that small
window brings it to the foreground, reducing their screen to the small
window - and removing your control of their mouse and keyboard.
way, while you're sharing screens, you also have audio chat
automatically enabled. If you're doing informal tech support, you can
be explaining what you're doing while you work with the remote user's
mouse and keyboard.
Very nicely implemented, easy to get up and
running, and easy to use. A good way for one Leopard user to be able to
help another Leopard user remotely.