ICMP Packet Format
ICMP header comes after IPv4 and IPv6 packet header.
ICMPv4 Packet Format
In the ICMP packet format, the first 32 bits of the packet contain three fields:
Type (8-bit): The initial 8-bit of the packet is for message type, it provides a brief description of the message so that receiving network would know what kind of message it is receiving and how to respond to it. Some common message types are as follows:
- Type 0 – Echo reply
- Type 3 – Destination unreachable
- Type 5 – Redirect Message
- Type 8 – Echo Request
- Type 11 – Time Exceeded
- Type 12 – Parameter problem
Code (8-bit): Code is the next 8 bits of the ICMP packet format, this field carries some additional information about the error message and type.
Checksum (16-bit): Last 16 bits are for the checksum field in the ICMP packet header. The checksum is used to check the number of bits of the complete message and enable the ICMP tool to ensure that complete data is delivered.
The next 32 bits of the ICMP Header are Extended Header which has the work of pointing out the problem in IP Message. Byte locations are identified by the pointer which causes the problem message and receiving device looks here for pointing to the problem.
The last part of the ICMP packet is Data or Payload of variable length. The bytes included in IPv4 are 576 bytes and in IPv6, 1280 bytes.
Internet Control Message Protocol (ICMP)
Internet Control Message Protocol is known as ICMP. The protocol is at the network layer. It is mostly utilized on network equipment like routers and is utilized for error handling at the network layer. Since there are various kinds of network layer faults, ICMP can be utilized to report and troubleshoot these errors.
Since IP does not have an inbuilt mechanism for sending error and control messages. It depends on Internet Control Message Protocol(ICMP) to provide error control. In this article, we are going to discuss ICMP in detail along with their uses, messages, etc.