IP Protocol, Routers, and Routing

If you have been reading all the posts, you are ready to get deeper into what happens behind the scenes on the Internet.  We are going to dig into certain protocols starting with the Internet Protocol (IP).  We will discuss how IP works to allow the transfer of information between computers on the Internet.

In our prior post, we talked about the IP address but how does the Internet Protocol itself work?  As an address system, it is used to route data to the right computers and servers.  An important concept to understand IP is to understand how data is sent.

IP Packets

Data across the Internet are sent in packets of data.  We won't get into the details until another post but let's cover the basic concept with a mail example again.  The US Postal system for example will only take packages and envelopes of certain sizes.  The Internet is a bit more strict about its envelope as in general there are not different sizes supported.

So, let's say the US Postal system only takes a single envelope with a single sheet of paper of a standard size inserted into it.  If you have a lot to say or a big book to send, you will end up using a lot of envelopes to send the entire communication through.  With the Internet, these "envelopes" are network packets which contain data.  These are more specifically, IP packets.  When downloading a web page there are multiple IP packets that must be sent to download the entire page.

Just like the US Postal system, IP requires a "to" and "from" address to know where to send the letter and from where the letter originated from.  As already discussed, this is the IP address for IP packets.  We will get into details of the IP packet later but just know that it contains the "to" and "from" IP addresses along with the data (limited in size) that you need to send.

Routers

Routers are the specialized devices that send these IP packets to the right destination.  They basically route the packet from you browser to Google's web server for example.  You can see examples of Cisco routers below (hopefully not too dated by the time you read this) though in data centers, there would be a lot of cables plugged into each.

Examples of Cisco routers

Across the Internet, there are routers.  For example, your Internet provider has routers within its network which in turn are connected to other routers which will eventually be connected to the router connected to Google's web server.  This is how computers all over the world are connected through this web of routers.

When a router is put into the Internet, it needs to be connected to other routers but in order to know how to route IP packets, it needs to be configured.  Each router will have a routing table.  The router will use this table to inspect the destination IP address and either send it to a server it is directly connected to OR to forward the packet to the next router to get closer to the final destination.  The following is a simple diagram.

Routers on the Internet forward data from your browser to destination servers and vice versa.  Grey arrows represent possible "next router" that packets can be forwarded to.  Green arrow shows the path that routers actually chose based on their routing table (note there are typically many more router "hops" between your browser and a web server).

Summary

Data sent across the Internet are done via IP packets which have both a source and destination IP address which routers utilize along with their routing tables to send the packet to the proper destination server.  For those who are more technical, I know a lot of detail is missing which we will dig into as we get more sophisticated.  

In our next posts, we will likely cover the TCP protocol.