TCP/IP, Keeping us connected. PDF Print E-mail
Written by Uan Spike   
Sunday, 06 July 2008 20:52
I had several ideas for this weeks column, but I thought I 'd explain a little of something I hinted about during my DNS column.  TCP/IP.   I was configuring another radio in my office yesterday and showing my two new techies a little about how this is done.  I realised during this conversation that I really am a Geek.  It wasn't a passing, “me, sure I like computers” it was a passionaite explaination of OSPF routing and how I love the way it's made my life easier routing packets around my network. 

What is TCP/IP. TCP/IP stands for Transmission Control Protocol / Internet Protocol.  We touched briefly on the fact that it was a form of phone number for your comptuer and a way of identifying a network adapter easier than a MAC Address.  Oh yes, it gets more complex.  A MAC address is the physical address assigned to your Network Adapter or Wireless Card, it stands for Media Access Control, but we won't get into MAC addresses right now.

Instead of giving you the whole history of TCP/IP and the details about Subnet Masking and IANA IP Address assigning. (IANA is the Internet Assigned Numbers Association) that controls who gets “real” IP addresses.  I'm going to give you some hints on how having no IP Address can make your network experience non-existant.

Please note that I'm talking about a network that provides plug and play access here, most DSL routers provide dynamic network addressing, also if you're in a corporate network environment I'm sure you also have dynamic addressing as static IP addressing is a real pain to manage.

When you connect to a network your NIC (Network Interface Card) will broadcast a request along the ether (Wireless or Wired) for an IP address.  This IP Address is assigned to your NIC by a DHCP (Dynamic Host Configuration Protocol) server.  Basically you computer walks into a network and shouts “Yo, I need a number over here”.  The DHCP server responds by saying “Hey, not so loud, this one is free.  Go forth and communicate”.  

The DHCP server is configured to give this computer all the relevant information it needs to talk to, not only computers on your own network, but how to get out to the internet or other networks beyond yours.  Lets check out your IP address, go to START, RUN, and type CMD then press enter.  If you're on Windows ME or 98 (I hope not) then type COMMAND and press enter.  This will take you to a dos box, don't worry, we're not going to far down the rabbit hole.

At the command prompt type IPCONFIG and press enter.  This will display your basic IP address information.   You should see now a list of numbers called IP Addresses and Subnet Masks.  I'll give you an example of a PC on my network if you're not currently behind a computer.  

Ethernet Adapter Local Area Connection
IP Address..............................192.168.1.57
Subnet Mask..........................255.255.255.0
Gateway.................................192.168.1.1

Excellent.  I'm not sure how this will be displayed in my column, but this should be a nice little list.  Now we know your IP address, your Subnet Mask (mine is class C) and the gateway.  What use is this you ask me?  Well.. this is the fun part.
If you know the IP address of another computer on your network, you can see if they have open file shares by typing START – RUN - \\192.168.1.57 (Their IP Address) and pressing enter.   If you're not getting out to the internet  you can run the PING command at the dos prompt (That little black entrance to the rabbit hole).  Ping is named after the sonar ping you see submarines using, it's to get to a destination and respond.  Ping is the foremost useful command in network troubleshooting I have ever used and should be your first stop to solving connectivity problems.

You run ping by typing the command and then a space and the destination you want to ping.  For example, your Internet isn't working. Get to the command prompt, run IPCONFIG.  Ping yourself.  ping 192.168.1.57  You should get four ping responses.  Your network card is ok, try pinging your gateway address  ping 192.168.1.1  If you don't get a response reset your DSL modem.  Problem solved. Or if your do, try pinging google.  ping www.google.com  This will do a DNS lookup, find the ip of google.com and then ping it.  Also, keep an external IP address on hold so you can see if your DNS server is down, so if ping www.google.com doesn't work but ping 203.97.33.1 (a external ip address) is up. Then you probably need to change your DNS settings.  

That's a start, ping and modified versions can be used for not so good Kung Foo like the Ping of Death, DDOS attacks.  TCP/IP gets us places, but also allows intruders to get to us, make sure you have a firewall to help filter out unwanted IP packets.  I'll try and discuss this another time.
 

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