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Hack 59 Make Servers Always Available by Mapping a Hostname to a Dynamic IP Address

Make sure that the web site or other kind of
Internet server you run at home is always available to the
world.

If you run your own web server, mail
server, or other kind of server at home and are connected to the
Internet via a cable modem or DSL modem, people frequently may not be
able to connect to your server. That's because,
typically, broadband ISPs assign you a dynamic IP address that
changes regularly, even if you don't turn off your
PC. Because your IP address constantly changes, there is no way for
people to connect to you. One day its IP address might be
66.31.42.96, the next it might be 66.41.42.136, and if people
don't know your server's current IP
address they won't be able to find it. You
won't be able to solve the problem by getting your
own domain (such as www.gralla.com) and
publishing that, because DNS servers won't be able
to keep track of your changing IP address either. If people type in
your domain name, the servers won't be able to
report on your IP addressand again, your server
won't be able to be reached.

There is a way to solve the problem, however: you can map your
server's hostname to a dynamic IP address. When you
do this, it doesn't matter that your IP address
changes; when people type in your web site's URL,
they will be forwarded to your new IP address automatically.

You can do this for free by signing up with a service that provides
automatic mapping. A number of services will do it for free, such as
No-IP.com
(http://www). When you
sign up for the service, you choose a hostname for your server and
give that hostname out to people who want to connect to the server.
Whatever name you choose will end in residential gateway at
home to share Internet access among several PCs, you may run into
problems using the service. Many gateways use
Network Address
Translation (NAT), in which all PCs on the network share a single
external Internet address but are assigned internal network
addresses. The No-IP.com client will track your external address, but
because that single address is used by all PCs on the network, not
just the server, incoming traffic won't be routed to
your server. You can fix the problem by using the port forwarding
feature of your route to send the incoming traffic to the
server[Hack #49].

You may run into another problem as well: when you try to test your
server by connecting to it from a PC inside your network, you might
not be able to connect to it. That's because you
might not be able to connect to the external IP address from inside
the network. If this happens, the only solution is to connect to the
site from a PC outside of your network or ask a friend to connect to
it.

One more thing to watch out for: if you're behind a
firewall, the No-IP.com
client may have trouble connecting back to the No-IP.com site to
report on your changing IP address. If you're using
a firewall like ZoneAlarm [Hack #48] or
a similar one that blocks outbound connections, tell it to allow the
client to make outbound connections. Also, depending on the firewall
you use, you may need to configure it to open TCP port 8245, because
that's the port the client uses to contact No-IP.com
with your new IP address.

5.19.1 See Also

[Hack #40]