What is an IP Header?

IP headers play an essential role on the Internet. They ensure the data sent to the destination and received from it is complete, correct, and in order.

Cisco defines an IP header as something that “contains the information required to route data on the Internet and has the same format regardless of the type of data being sent.”

This article will cover everything you need to know about an IP header. Read on.

Understanding IP Header and How It Works

An IP header refers to the information included at the beginning of an IP packet. 

This information includes details such as:

• IP version
• Packet length
• IP addresses (Source and Destination)
• Time-to-live

If you're unfamiliar with IP packets, they are the tiniest messages exchanged on the web. 

You can think of these packets as actual packages. A package contains two things: the content inside and the label outside.

The contents inside are the data you receive and send to another server. Meanwhile, the label outside is the header. 

An IP packet header gives information to describe the data in the packet for accurate receiving, processing, and returning. 

With the details, you can ensure proper and efficient sending and delivery.

IP Header Fields

You'll find several header fields depending on the version of IP. Each header field includes essential information about the transferred data. 

Since IPv4 and IPv6 have different headers, take a closer look at each one:

IPv4 Header Field

You can find 13 fields in an IPv4 header. Here's what the IP address header format looks like on an IPV4:

To better understand IPv4 header fields, check out the table below:

IPv6 Header Field

An IPv6 header only has 8 fields. The address size in this header is four times bigger than IPv4, but the header itself is only two times bigger.

Here's what an IP address header format looks like on an IPV6:

Check out how each field works using the table below:

IPv4 and IPv6 Header

The headers for the two IP types differ in many ways. For a better comparison, here's a side-by-side comparison between IPv4 and IPv6 headers:

Here's a breakdown of their differences in every comparable aspect:

Field Number

An IPv4 header includes 13 fields, while an IPv6 header only has 8. 

Some fields, like the identification field in IP headers, are only available in an IPv4 header.

Size

Despite having more fields, IPv4 headers are smaller—at around 20 to 60 bytes. It will only be more massive if you use the options field, which rarely happens.

Meanwhile, IPv6 headers are twice as big as IPV4 at around 40 bytes. Unlike the expandable IPv4 header, this one has a fixed size.

Address Size

The main difference between the two headers is the space for the IP address size.

An IPv4 header has a 32-bit field, covering 4.29* 10^9 addresses. On the contrary, an IPv6 header has a 128-bit field, which can cover 3.4 * 10^38 addresses.

Use of checksums or flags

The IPv4 header has a field for flags or checksums, while the IPv6 header has none. It means IPv6 does not use such fields.

Here’s a table to summarize the differences between the headers of the two versions of IP: 

TCP Header vs. IP Header

Transmission Control Protocol (TCP) works with IP to show how data exchange happens on the web. 

With different tasks and purposes, the headers of TCP and IP differ from each other. 

To understand their difference, here's a comparison:

 

Here are the main differences between the TCP and IP headers:

Field Number

A TCP header includes only 10 fields (with one optional field), while an IP header has 13. 

However, when compared with an IPv6 header, a TCP has more fields since IP’s latest version only has 8.

Header Size

TCP and IPv4 headers have the same size of 20 to 60 bytes. 

Comparing a TCP header to an IPv6 header, TCP is smaller because IPv6 has 40 bytes.

Purpose

The IP sends each packet to its destination. Meanwhile, TCP ensures the transmission is correct, complete, and orderly. 

When combined, they work as TCP/IP.

Options Field

TCP has a higher capacity in its options field, up to 320 bits. 

Meanwhile, IPv4's options field can only have up to 32 bits. Moreover, IPv6 has no optional field.

Below is a table to sum up the distinctions between the two headers: 

Conclusion

IP headers contain details ensuring efficient, correct, and orderly data exchange. 

With these, every piece of data you send and receive will be detailed and accurate. 

As a result, the servers can understand the data, its source, and the process it needs. These headers have different layouts depending on the versions. 

Nonetheless, every type of header shares the same purpose. It ensures the data exchange will be smooth, error-free, fast, and orderly.