When looking into the field of Ip packet headers, you will find a section titled Upper Layer Protocol. In this section, there is a field labeled UDP and TCP. These are two of the most common upper layer protocols that are identified.
UDP stands for User Datagram Protocol, and TCP stands for Transmission Control Protocol. These names stem from how they were developed.
How were these protocols developed? What do they do and what is their value? This article will explore these questions and more as we dive into what UDP and TCP do, and how they work.
Both UDP and TCP are used to send information across networks from one device to another. Because of this, both play an important role in transmitting information across networks.
IP version 4
The next field in the IP packet header is the IP version 4 field. This field identifies which version of the IP protocol this packet uses.
Versions of the Internet Protocol have been updated over the years as new features are added and to address security concerns. The most recent version, IPv4, is the standard used across the world today.
All devices that interact via IP use a specific version of the protocol. For instance, devices such as computers, phones, and routers use IPv4. Domain name servers (DNS) use IPv6 instead.
By checking this field, the receiving device can determine what actions to take based on what protocol it uses. If it is an older protocol, it can switch to older protocols so that it can properly handle and send back the data contained in the packet.
IP version 6
The next field in the IP packet header is the IP version 6 field. This field indicates whether the packet contains data pertaining to the IPv6 or IPv4 protocol.
If the data contained in the packet is encoded in IPv6 format, then this field will read IPv6. If the data is encoded in IPv4 format, then this field will read IPv4.
Because of how pervasive IP addresses have become, most applications no longer check this field. If an application is looking for a certain type of data and does not find it, it may throw an error or perform other actions as a result.
Checking for errors like this can be helpful when trying to solve problems with your computer. If your computer is having issues connecting to places on the internet, checking if this error is due to an incorrect protocol on the computer side or if it is due to an incorrect protocol on the outside source can help solve it.
Fragmentation and coalescing
Another key feature in the IP header is the fragmentation and coalescing field. This field is located just before the destination IP address, in the header.
When a router receives a packet, if the packet is too large for the network pipe it must pass through to get to its destination, it will fragment the packet.
A smaller packet will be created, with some metadata added that identifies which original packet this new packet is a part of. The router then sends this fragmented packet out onto the network.
When a device receives a fragmented packet, it must reassemble all of the parts into the original wholepacket so that it can then send it onward to its final destination. Devices on the network that can do this are called routers.
The value in the upper layer protocol field identifies what kind of protocol is located in the payload ofthe IP datagram.
Header validation
Another function of the IP layer is header validation. When an IP packet is received, the receiving device checks the source and destination IP addresses and verifies that the packet was sent by a trusted source and was intended for its receiver.
If the source or destination IP address is not recognized, then the packet is discarded. If the data within the packet does not match what is expected (i.e. correct data format), then it is also discarded.
This prevents unauthorized sources from sending data to a receiver for processing, as well as ensuring that only intended data is processed. For example, if a malicious user wanted to send false information to a computer processing weather data, header validation would prevent this misinformation from being processed as accurate data.
This protocol also checks that the length of the IP packet matched what was expected based on other protocols in the upper-layer protocol field. If it does not match, then it is invalid.
Source address
A source address is what IP addresses your device uses to contact or “send” something to another device. This can be in the form of a phone call, text message, email, or in this case, a packet.
The source address identifies the device that is sending the packet and its location. All devices that send packets must have an IP address, making this field very important.
When you send a packet, your device looks at the destination address (who it is going to) and then assigns its own IP address as the source address. This makes sense because the device needs to send it from somewhere, doesn’t it?
All devices use their own internal IP addresses to function; they just show different ones on the outside depending on what type of device they are. Devices like phones and tablets use mobile devices as their internal IP addresses.
Destination address
The next field in the IP header is the destination address. This field identifies the destination device that the packet is being sent to. This can be a computer, a server, or another electronic device.
The destination address is a combination of numbers called an IP address. An IP address is structured in different ways depending on the protocol used to assign them.
They can be structured as hexadecimal values or decimal values between 1 and 255. Both of these are 8-digit numbers that represent a unique device.
They can also be structured as quad-octet values, where each octet is a group of 8 digits. These are all combined to make a 32-digit number that represents a unique device.
An IP packet does not require a destination address, but it must have one if it is being sent to another device.
Protocol type
A protocol is a set of rules that both computers and programs use to communicate with each other. These rules are developed and adjusted by computer programmers across the world.
Many different types of protocols exist, some more important than others. Some common internet protocols include TCP, UDP, ICMP, and HTTP.
The way you identify a protocol is by the name in the upper layer protocol field in the IP packet header. This field identifies what type of data is being transmitted.
ICMP is one of the core internet protocols and it communicates messages such as destination unreachable or echo reply. TCP and UDP both transfer data from one place to another, but they have different identifying characteristics.
Header length
The next field in the IP header is the header length field. This field indicates the length of the IP header. It also indicates how many more headers are included in the packet.
This is important information for both decoding and encoding of packets. Decoding packets needs to know how many headers are in the packet so that it can read and interpret all of them correctly.
Encoders need to make sure they add enough space for all of the headers so that none of the data in the rest of the packet is damaged or corrupted.
The length of the IP header is set to 5 bytes. This makes it a 20-byte header, including all of the fields within it. It only takes up a small portion of the total packet size, making it easy to identify.
