What is TCP?

TCP (Transmission Control Protocol)

Transmission Control Protocol (TCP) is a communication standard, one of the first internet protocols (TCP/IP). It is connection-oriented, for all kind of devices and applications to exchange messages through a particular network. 

Data is organized in a specific way by TCP to be transmitted between client and server. The purpose is to protect the data on their trip around the network from the sending to the delivery.

TCP is a very popular protocol in network communications. 

How does it work?

Transmission Control Protocol (TCP) was created for sending packets on the Internet, making sure the proper data and messages’ are delivered through networks. It works through a process that involves different steps. 

As mentioned previously, TCP is connection-oriented. This means it has to make sure the connection between source and destination is not only set, but also kept until the whole exchange of data (sending and receiving of messages) is completed.

Thus, the first step is TCP sets the connection needed by a source and its destination. During this period, there’s a connection, but there’s not data transmission yet. 

Then communication starts. TCP gets messages from the sender (server or application) and split them up into packets. TCP organizes the chopped data with numbers to have control over all the packets and protect messages’ integrity. 

Already chopped and numbered, messages will go to the IP layer for transporting. They will be sent and re-sent by the different devices involved in the network (gateways, routers, etc.) until they reach their destination. All packets belonging to a message have the same destination. But they all can travel following a different route. 

As soon as they arrive, they are rebuilding. Yes, through the numbers assigned to every message’s packet, it puts all packets together again. 

Once messages are built, they are delivered to their recipient. 

You know that network congestion, traffic load balancing maneuvers, and other factors can affect networks’ performance. TCP can solve those problems if such causes affect packets and get duplicated, disordered, delivered, or lost. The protocol can identify the specific issue, then request the lost data to be transmitted again, and reorganize in the proper order, disordered packets.

If, after fixing problems, messages still don’t get delivered, the source is informed about the failure.

Without a doubt, Transmission Control Protocol (TCP) is a reliable standard and a key for the Internet to work better and more precisely. 

There are different protocols, but if you need accuracy and you can’t afford the loss of data (packets), TCP is ideal for you. That is why it is widely used by very well-known Internet applications like SSH (secure shell), FTP (file transfer protocol) or IMAP (message access protocol), SMTP (simple mail transfer protocol), HTTP (hypertext transfer protocol).

Advantages of TCP

  • It guarantees accurate end-to-end data delivery. The bytes received will be the exact ones (same order) originally sent. 
  • Its functionality includes not only issues’ detection (duplicated, lost packets, etc.), but also the ability to fix them.
  • It operates with network congestion avoidance, an algorithm that includes different mechanisms to control congestion problems (AIMD, congestion window, slow start…).

Disadvantages of TCP

  • It is focused on accurate delivery, and that takes time. TCP’s process and additional fixing of problems, in case they occur, can cause delays. We talk about seconds or milliseconds, but in the context of a demanding world (Internet), that can mean much.
  • It’s not a choice for real-time applications like voice-over IP or streaming media. The reason is TCP’s process doesn’t have a fast transmission as a goal.

Conclusion

TCP is a reliable tool, very popular on networks. If it is about accuracy for delivering data, no doubt TCP is the choice. 

DNS TXT record explained

DNS TXT record

There are a lot of DNS record types, at least 50 out there! One of them is called DNS TXT record, and it has a variety of purposes. Yes, it is one simple text record, but it is widely used, so let us explain the TXT record.

TXT record explained

TXT record is a DNS record type that has text information designed for external to the domain sources. The text could be written for people, so it would be easy to read, has enough information and logically organized, or made for computers, and has a more technical format.

Usually, you will see, inside the TXT record, a piece of general information about the domain and an additional part for a particular type of validation.

What’s inside a DNS TXT record?

There are just a few fields that you can manage:

  • Host: Hostname/ domain name, for which we are creating the TXT record.
  • Type: TXT – the DNS record type.
  • TTL: Time, that this record is cached on the recursive server.
  • Points to: Here, you can put a different value, depending on the purpose you decide.

Why do you need a TXT record?

The TXT DNS record has multiple purposes and can work with different software, including various email verification methods for incoming and outgoing email servers:

  • SPF – Sender Policy Framework is a method for authentication of emails, checking which of the servers has the right to send emails for a domain and has different mechanisms in case of wrong sender parameters.
  • DKIM – DomainKeys Identified Mail. It is a cryptographic authentication method for signing mails and proving that they are coming from a particular domain.
  • DMARC – Domain-based Message Authentication Reporting and Conformance is a security mechanism that proves who the sender of an email is and lowers the number of spam messages.
  • Verification for software – Big companies like Microsoft (Office 365), Google and more, need you to add a TXT record in your DNS zone to prove it is yours. It combines the SPF and DKIM authentication and works with them.

How to probe TXT records

We will use Wikipedia.org for checking their TXT records, but you can just replace it with your domain name and see your TXT records.

Check TXT record on Windows

Open the Command Prompt. Press “Windows key + R”, the Run application will start, and there you can type “cmd”, and press the Enter button. Inside the Command Prompt, we will use the nslookup command.

nslookup -type=txt wikipedia.org

Check TXT record on Linux and macOS

On Linux and macOS, there are many ways that you can check the TXT DNS record. All of them will involve using the Terminal application, so please start it. 

Dig command on Linux and macOS

Dig command is one of the most powerful tools for performing dns queries and debug your dns configuration, for example – what are your current TXT records. Here are some examples how to check the TXT record for a domain name:

dig wikipedia.org TXT

or you can use a specific one to check the DMARC record:

dig _dmarc.wikipedia.org TXT

Host command on Linux and macOS

host -t txt wikipedia.org

Conclusion:

After this article, you should know what the TXT DNS record is, why does TXT record exist, how to check the TXT record so we can easily say, TXT record explained! 

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