The Internet: routing and name resolution

The topology of the internet is a mix of , and fully networks.

For example, connects most colleges in Ireland while connects most colleges in the UK.

They key aim of the internet is that it should ideally be possible to reach any on it from .

For routing to work, IP addresses must be (i.e. having . This is comparable to the first letter of room numbers). tables () must be established.

The is the simplest routing table of all: it sends all traffic to a specific on the , and lets the deal with it from there.

The internet and the world wide web are not the same thing! The web is a particular that runs over the internet.

From early stages in its development, users preferred to refer to other hosts by rather than . This means we need a way to resolve a name into an .

When a host needs to be contacted by , the process is in order: firstly, it must be checked if the /IP mapping is from before.

The is read on to see if there's a matching entry.

The configured is then checked for the IP.

Once the name is known, packets are either or is done and packets are sent directly as before. On most operating systems, the or commands can be used to directly query an IP address for a hostname.

What does the acronym DNS stand for: .

The provides a way to look up any host on the internet by it's fully qualified domain name. Only the of a DNS server is needed, which is usually on our .

So that the DNS system could be , it was decided that each host would have a unique within a given name. For example: printstaff01.ad.dkit.ie means that the hostname is and the domain name is

The acronym TLD stands for .

An example of a TLD is or

Using the previous example of printstaff01.ad.dkit.ie, is a subdomain of which is a subdomain of the domain.

When a local DNS server on a network is asked by a client to resolve a , it go through the subdomains, starting with the and the on the right. For each subdomain, it will get the of the DNS server for that subdomain, which it will then .

Ports allow us to identify to a what service a packet should be sent to when it gets there. Each packet is tagged with the port so that the receiving computer knows .

Common internet port numbers include for DNS lookup, for Windows Remote Desktop and for Secure Shell.