Addressing: IP and DNS
IP Addressing
Every device connected to the Internet has a unqiue (IP) address that identifies it on the network. This is a numerical address that is expressed as 4 sets of numbers in the range 0.0.0.0 -> 255.255.255.255. No two devices on the network can have the same address, otherwise there will be confusion as to which machine the information is to be routed to. This numbering scheme is referred to as IPv4.
In order to co-ordinate this number assignment, the Internet body, RIPE, co-ordinates the allocation of these unique addresses to various organizations and ISPs, which then in turn manage their block of addresses for individual assignment to devices under their control.
The present IP system allows for up to 4,228,250,625 (255 x 255 x 255 x 255) unique addresses. However big that number may seem, we are running out of them. Any device that needs to connect to the Internet needs a unique address - this includes desktop computers, network routers, mobile phones, PDA's and even some vending machines.
A new Internet Protocol is currently being introduced known as IPv6. This builds on the older addressing scheme (IPv4) by adding an extra pair of addressing digits. So the new format is 0.0.0.0.0.0, yielding over 1,162,523,670,191,533,212,890,625 unique addresses. This new addressing scheme has been designed to cope with even interplanetary networking. In other words, Mars and Jupiter now have their own IP address range!
DHCP (Dynamic Host Configuration Protocol)
It was quickly realized that not all machines needed an IP address all the time. Only when they were connected to the Internet was an IP address required. In response to this, a new protocol was designed that would allow a machine to ask for an address to use and once they were finished, the address would be returned to the pool of available addresses. This was particular useful for dialup users who would find themselves on the Internet for only a few hours a day. This protocol is known as DHCP. In addition to assigning an IP address, it can also give the machine all the other network type of information it requires.
This solved a number of problems in one swoop. It solved the shortage of IP addresses, by allowing machines to borrow addresses. It also solved the complicated setup for non-computer literate users. It was all done for them. Many ISPs use DHCP for their clients to connect to the network, for example AOL and BT are two classic users of DHCP.
DNS (Domain Name Server)
Human beings are notoriously unreliable machines that have a tendency to forget details. To stop people from having to remember "ugly" 12 digit numbers, domain naming was invented. This was a system that would map a given name onto an IP address. This way people didn't have to remember the IP address. It was a shortcut to the real underlying address. The DNS system was invented in 1981 (some 10 years prior to the introduction of the World Wide Web) as a way to make routing email much easier.
Every time your machine makes a request to a website, for example www.google.com, the browser doesn't know which IP address to connect to. It has to ask the DNS server which IP address www.google.com points to. For this example the DNS server would return 216.239.37.101 as the real IP address in which the browser must make a connection to. This all happens behind the scenes and very quickly. The DNS system was designed to be as fast as possible, so the lookup delay is minimised as much as possible.
Basic IP tools
Most computer systems give you access to a couple of special IP utilities; pingand tracert. To run these utilities you must open up a Command Prompt in Microsoft Windows or a Console if on Linux. The ping utility (shown below) acts very much like the submarine sonar-ping that it is named from; it pings a machine to see if its responding.
C:\>ping www.google.com
Pinging www.google.com [216.239.37.101] with 32 bytes of data:
Reply from 216.239.37.101: bytes=32 time=157ms TTL=52
Reply from 216.239.37.101: bytes=32 time=172ms TTL=52Ping statistics for 216.239.37.101:
Packets: Sent = 2, Received = 2, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 125ms, Maximum = 172ms, Average = 144ms
We ping Google's main site and we can see that even the ping utility has to resolve the name to an IP address before it can connect to it. The ping utility then sends a small packet of data (32bytes) to the machine and records the amount of time it takes to come back (in milliseconds). Generally a machine that is considered alive will return the packet.
The Internet is a series of interconnected nodes that forward and relay packets of information. You can trace this route using the tracert utility. Running this on our google address we have the following output:
C:\>tracert www.google.com
Tracing route to www.google.com [216.239.37.101]
over a maximum of 30 hops:1 62 ms 125 ms 47 ms bthg501-hg2.ealing.broadband.bt.net [217.32.137.73]
2 62 ms 79 ms 93 ms 217.32.137.1
3 109 ms 94 ms 63 ms host217-32-137-106.webport.bt.net [217.32.137.106]
4 62 ms 94 ms 78 ms inh3cs01-500.imsnet3.btopenworld.com [213.1.119.61]
5 63 ms 62 ms 47 ms btfl03-gig8-7.imsnet3.btopenworld.com [213.1.119.153]
6 * * 78 ms core2-pos12-1.ealing.ukcore.bt.net [194.72.9.201]
7 156 ms 157 ms 109 ms transit1-pos4-0.ealing.ukcore.bt.net [194.72.9.238]
8 187 ms 204 ms 187 ms transit2-pos9-0.washington.ukcore.bt.net [194.72.9.30]
9 172 ms 328 ms 172 ms eqixva-google-gige.google.com [206.223.115.21]
10 218 ms * 172 ms 216.239.48.193
11 203 ms 234 ms 188 ms 216.239.48.89
12 125 ms 125 ms 125 ms 216.239.48.94
13 125 ms 125 ms 141 ms www.google.com [216.239.37.101]Trace complete.
When this was run, there was only 13 hops between the client and the Google server. As you can see, traffic was routed from London, over to Washington and then over to Google, which is located in San Francisco. You can also see all the individual IP addresses of each node along the way.
Thetracert utility is very handy to use if you suddenly experience a slow download speed. You can tracert to the server you are connecting with and see which hop has the slowest response time. The overall speed of your download is only as fast as the slowest hop. This utility will pinpoint that for you.
Apple Mac Specifics
On a Mac running OSX there are 2 ways of accessing network tools. Within the Grapic User Interface (GUI) you will find the Network Utility in the Utilities folder within the ApplicationsPing
and Traceroute
In addition to the Network Utility those familiar with the Command Line Interface (CLI) can apply the same commands using the Terminal(/Applications/Utilities)The Terminal application uses mainly standard BSD commands with some Mac add-ons. Hence in this instance the Unix commands Ping and Traceroute will provide the same information as above in the Network Utility. To find the secondary commands and necessary suffixes look at the man pages for each command within the Terminal. The following demonstrates from the initial command at the Unix prompt
$ traceroute www.apple.com
traceroute to www.apple.com.akadns.net (17.112.152.32), 64 hops max, 40 byte packets
1 192.168.0.1 (192.168.0.1) 3.815 ms 1.814 ms 1.930 ms
2 loopback1.ar1.he1.systems.pipex.net (62.241.161.241) 48.274 ms 58.069 ms 44.091 ms
3 ge-1-0-0.cr1.he1.systems.pipex.net (62.241.161.118) 22.171 ms 21.227 ms 22.411 ms
4 ldn-b2-geth6-0-12.telia.net (213.248.100.97) 20.828 ms 20.449 ms 21.661 ms
5 ldn-bb1-pos0-2-0.telia.net (213.248.64.77) 105.027 ms 44.304 ms 36.548 ms
6 nyk-bb1-pos0-2-0.telia.net (213.248.65.90) 92.072 ms 89.751 ms 90.547 ms
7 chi-bb1-pos6-0-0-0.telia.net (213.248.80.153) 111.519 ms 112.131 ms 111.439 ms
8 sjo-bb1-pos1-0-0.telia.net (213.248.80.26) 167.308 ms 155.347 ms 156.153 ms
9 att-sjo-bb1.telia.net (213.248.86.62) 160.005 ms 158.533 ms 156.774 ms
10 gbr2-a90s44.sffca.ip.att.net (12.123.12.6) 163.698 ms 174.469 ms 167.903 ms
11 12.122.80.177 (12.122.80.177) 165.508 ms 163.202 ms 163.459 ms
12 12.124.34.38 (12.124.34.38) 164.294 ms !X * 163.545 ms !X
For Macs using systems from OS 7.5.3 up to OS 9.22 there are 3rd party utilities such as MacPing available which you can use to perform these functions.
For more information: