Re: BBC TV 4 - Hawkwind: Do not panic

Rowland McDonnell <real-address-in-sig@xxxxxxxxxxxxxxx> wrote:

But do you have any idea how do I find out what a port *is* (I've never
got to the bottom of it), what `forwarding a port' means, or any idea
how I find out how to make the required changes to my router's setup?
The `helpful' BT leaflet explains that I don't need to touch my router
settings unless told to by the helpdesk - so, erm?

By default, routers only let in data that's been requested by you. If,
however, you're running a server then there will be requests to connect
from third parties as well. In that event you will need to 'forward' the
port on the router.

Let's take an example of a web server. The web works on TCP port 80.
Let's say you run a web server off your Mac, which has a local IP
address of 192.168.1.1

What you need to do is go to the port forwarding section of your router
(sometimes called 'Virtual Servers') and create an entry. Typically the
fields you fill in are source and destination port (both 80 in this
case), data type (TCP, UDP or both - choose both) and destination IP
address (192.168.1.1 in this case). Then, whenever someone types in your
external IP address into browser (212.159.71.78 say) the request to
connect gets sent to that IP (which is your router), the router says
"ah, incoming traffic on port 80 - I've got to pass that on to
192.168.1.1" and does so. In effect you're telling the router that
traffic on a certain port needs to be passed on to a certain IP address
on your local network unmolested.

The text file '/etc/services' contains a list of port numbers/services.
Typing "cat /etc/services|grep http" into Terminal.app would list the
entries that contain 'http'. There's actually rather more of them that I
expected, but 80 is the first entry.

For ftp you need to forward both ports 20 and 21, TCP and UDP to be safe
(because I can never remember what ftp uses - surely TCP?). FTP can be
tricky though because there's two kinds, 'active' and 'passive', and
20&21 only apple to 'active'...I think.


That's probably not helped much. Sorry.

Jim
--
Find me at http://www.ursaminorbeta.co.uk
AIM/iChatAV: JCAndrew2
Skype: greyarea
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