Posts Tagged Networking

How DNS Works?

DNS = Domain Name System or Service or Server

DNS resolves/maps a Name to an IP address

The diagram below describes the functionality of DNS. It also elaborates on what goes on behind the scenes once you type in a certain URL (Uniform Resource Locator) or a web address in your browser. The whole DNS process is based on the following 2 components:

  • DNS Query (Question)
  • DNS Reply (Answer)

(Click on the Picture Below to Enlarge)


, ,

1 Comment

Most Common TCP/UDP – Transport Layer Ports!!!


, ,

No Comments

What is MPLS & Why is BGP required with MPLS Implementation?

FYI… The below-mentioned explanation is a very high-level overview of how MPLS & BGP work in conjunction. This post, by no means, contain detailed information regarding MPLS & BGP. If you need more information check out Cisco’s site (search keyword: MPLS, BGP) & you will find tons of material with great explanations.

MPLS (Multi-Protocol Label Switching) is basically a WAN technology that allows Routing on Layer2. Now I know, this sounds crazy but just hang in there for moment & I will explain myself. Review the below-mentioned diagram while keeping the OSI Model in mind & it will give you an idea:


As you can see, MPLS is stuffed between Layer2 (Data-Link) & Layer3 (Network), therefore its considered “Layer 2.5” Protocol. Do understand the underlying WAN mechanism or infrastructure is still based of off Layer 2 technologies such as Frame Relay, ATM, PPP, HDLC, etc. MPLS essentially adds the concept of Labels, which makes it a lot quicker to deliver packets to its destination since the Layer3 lookup is not required.

Now where does BGP come into play? Why is BGP required with MPLS Implementation? These questions come to mind because with Frame Relay, ATM, PPP, HDLC we did not need a Layer3 routing protocol. Well, here is the answer:

With strictly Layer2 WAN protocols provided by the service provider or carrier, we only need Layer2 information since we (customers) need to communicate to the provider on Layer2. With MPLS however, things are a bit different. The provider now communicates via BGP. In other words, in the old days provider would only care about Layer2 stuff & the upper layers were our responsibility as far as routing. But with MPLS, the provider now participates in the Routing process & is running BGP on their router. Hence we also have to use BGP on our router for the MPLS to work.

The following WAN Designs will further clarify the above explanation:


, ,

1 Comment

How do Packets Travel? What’s the Force behind the Internet or WAN?

A mystery-seeking mind often wonders how does the internet work? What causes the packets to travel? What is it that pushes the packets or causes the spark, if you will?

Well the answer lies in the basics of Network Communications & the depths of Laws of Physics. Here is a scenario: you open up an internet browser & type in a URL. Here is what happens from Network/Physics perspective –>

As soon as you open the browser & type in the URL, a slue of network packets travel from your PC to the Local Area Network or LAN. Here it is piece by piece, in terms of what happens:

  • Application Layer (Layer 5, 6 & 7) sends a request to Transport Layer i.e. Layer4 of the OSI Model (
  • Layer4 creates a network socket by combining source ip, destination ip and a TCP or UDP Port # associated with the request. (
  • Layer3 on the LAN segment gets the request from Layer4 & sends the IP information down to the LAN device (switch).
  • LAN Switch grabs the info & processes the data by forwarding it to the WAN device i.e. Router (could be DSL modem, cable modem, t1 etc.)
  • Router grabs the Layer3 info & forwards the request over to Layer2 device i.e. WAN device on the provider network. It could be an ATM or a Frame Relay switch.
  • The provider then forwards the request to the requested host on the internet i.e. a server you are trying to access. That’s the server you requested to connect to when you typed in the URL in your browser.
  • The server replies back to the provider, then the provider forwards the reply back to you.
  • The Router (WAN device) in your network forwards the information back based on the network socket info & eventually you get to see the site you requested.

Now the above-mentioned explanation is a very high-level overview of basic internet (WAN) communication. However, there is a big mystery about Layer1 that typically remains un-explained. I will try to address this here to the best of my knowledge:

There you go. Here is an answer to the mystery force causing the information to flow through wires across the globe. If you want to dig even deeper & zoom into each electron to get a sub-atomic picture, go for it. Here is the link:

If you grab a magnifying glass & zoom into each sub-atomic particle (like Electron) you will find out that there is something called “energy flakes or strings” that compose the Electron to define its physical characteristics. Everything in this world that physically exists on a super-microscopic level is made up of these energy strings. Here is the link for the curios:

Good Luck!