How the Internet Works

Before we dive into, how the Internet works, we first need to understand the infrastructure behind it.

Lets first learn about the Submarine Cables!

Even in the age of cloud computing, the world of the internet is connected by Fiber Optic cables that are also known as the Submarine Cables.

These Submarine Cables are huge Fiber Optic Cable Wires that run across the ocean, interconnecting countries together with the internet.

• The following map shows the submarine cable which connects the world via the Internet.

While most modern countries have multiple submarine cable’s running across their territories, smaller island nations often have a single submarine cable running into their territory. 

Having multiple submarine cables running into your country means you have a failover redundancy in place, in the case that one of the submarine cables goes down for any major reasons.

Example : If my company has 2 ISPs that use both the same submarine cable, it could cause a problem. Recommended using 2 different ISPs, using 2 different submarine Cable.

Real Life Example:

An Island Country called “Tonga” was impacted due to damaged submarine cable. Because there was only one submarine cable going into the country, when a volcanic eruption destroyed the only fiber that connects the country to the internet, Country of Tonga was isolated from the Internet for nearly a month.

https://www.bbc.com/news/world-asia-46968752

We talked about what submarine cables are, now lets talk about Landing Point.

This is the point where the Fiber Optic Cable that runs via submarine are coming into the Land, where Fiber Optic Cable’s will be available for ISP or 3rd party to lease. At this point, an ISP entity will purchase or lease these optical fiber cables, which will then connect back to their data centers.

Generally, these fiber optic cables will connect back to ISP Data Center’s core routers and which will traffic across the entire world.

A powerful device is generally needed, to send traffic one way to another. And this is why core router is generally preferred.

• A core routers job is simple, to send traffic one way to another fastest as possible.

From the one large optical fiber cable that derives from the landing point, there are smaller derivations of cables, which we connect back to our ISP’s.

Refer to the picture below

Lets assume that the optical fiber cable pipe is 100Gbps. This capacity can be distributed into smaller portions for ISP to use, in accordance with their needs.

We covered some of the Big Key Players in how the internet works so far

• Submarine Cable

• Landing Point

• ISP Role

 Now I would like to show you how it connects back to our corporate environment.

• Routing (BGP)

• DNS

• NAT

Lets start!

Before we dive into what a BGP is, we first need to talk about the Edge Device.

What is an Edge Device?

Simply put, an Edge Device usually refers to the Edge router which is a device that is used to connect to other networks outside of our domain.

• Its usually the last internally managed routing device that separates one network to another

The Exterior Routing Protocol that is used, to connect to other networks outside of our domain is called the BGP.

• Although we can use Interior Routing protocols to communicate to our outside domain, we prefer to use BGP because of its scalability.

BGP Is most widely used when dealing with ISP or any big companies.

• Using BGP, companies are easily able to manage hundreds of different subnets.

• Routing Protocols such as OSPF, simply does not have the level of scalability as BGP and thus generally used to route internal traffics which consist of smaller set of connected networks.

Now the fun question, so how does BGP actually helps us to communicate with the outside world?

• Through something called a BGP Peering, Through BGP Peering we can form a neighbor-ship with the ISP Router or other organizations.

  • Direct exchange of traffic via the internet.

• Also Through BGP Peering, we have availability to other networks IP Addresses and we use DNS instead of IP Addressing to address them.

  • For visibility purposes and instead of relying on IP Addressing which is harder to tell, if something ever goes down

Now that we talked about, how corporations connect to the Internet, we need to know something about IPv4 and its Exhaustion

• What is IPv4 Exhaustion? And why should we care?

History Lesson:

• Back in the days, your home devices consisted of multiple Public IP addresses, because originally 4 billion IPv4 Addresses were thought to be enough for human kind. (Clearly not). Thus, IPv6 was invented but I will not get into that this blog post.

• In order to conserve quickly depleting public IP addresses, we use a protocol called NAT which converts public IP Address into a private IP Address.

• IANA (Internet Assigned Numbers Authority) also Reserved what is known as “RFC 1918” which ensures that, the address allocation for private internets use the following reserves.

  • Reserve 10.0.0.0/8 | 172.16.0.0/12 | 192.168.0.0/16

• Basically means, No ISP will ever advertise these IP Address schemes as a Public IP Address. These are strictly for use of Private & Within an Organization.

• IANA = One of the Internet’s oldest institution and they own database that stores all internet domain names.

Now Lets talk about the difference between Public IP Address and Private IP Address

• Public IP Address : Can either be provided by an ISP or alternatively, you can purchase an IP Block from the Internet Gods also known as IANA.

• When talking about private IP address, we need to address something called a NAT.

• The rule of thumb, is that that the ISP will provide a public IP Address to first establish communications with our network. This is where we use something called “NAT” which is also known as Network Address Translation. Simply put, it translates a public IP Address to a Private IP Address.

• To conserve IP address spaces, we use different type of NAT protocols.

• NAT Overload (PAT) Port Address Translations– Takes 1 Public IP Address, and using private ports you can assign many private IP Address, as long as the private ports are not in use.

• NAT Pool – Sort of like how a DHCP works, you can setup rules to translate our private IP to the public IP address. 

Example:

• If you have 2 ISP, and you want to use Active / Standby System, you can use NAT Rules that are translating your private IP into the first primary Public IP and If something happens to the primary ISP, than you can have another NAT Rule setup that will translate our private IP to the public IP Address that was provided by our 2nd ISP. (In this case, there is 2 NAT rule in placed – Active / Standby Sate)

Alternatively, SD-Wan is the latest technology, that can be an alternative solution where the network can use multiple connectivity options including ISP circuits etc.

Thank you for reading!

- Chris