ICMP - cysec-all-in-one(A.R)

Here’s a concise cheat sheet for the Internet Control Message Protocol (ICMP), including information about its types, error handling, and queries presented in tabular format for clarity.

ICMP Cheat Sheet

Overview

ICMP (Internet Control Message Protocol) is a network layer protocol used by network devices to send error messages and operational information indicating success or failure during communication.

Common Uses

Error Reporting: Notify hosts of issues in communications.
Diagnostics: Used in tools like ping and traceroute.

ICMP Types Table

ICMP Type	Description	Code	Common Usage
0	Echo Reply	0	Respond to ping requests
3	Destination Unreachable	0-15	Indicate unreachable hosts/ports
4	Source Quench	0	Request sender to decrease transmission rate
5	Redirect	0-1	Notify hosts of better routes
8	Echo Request	0	Initiate ping requests
11	Time Exceeded	0-1	Indicate packet hop limit exceeded
12	Parameter Problem	0-1	Indicate an issue with header parameters
13	Timestamp Request	0	Request timestamp from the destination
14	Timestamp Reply	0	Respond to timestamp requests
15	Information Reply	0	Not commonly used

ICMP Error Handling Table

In the context of ICMP (Internet Control Message Protocol), the numbers 3 and 0 refer to specific fields in the ICMP message that indicate the type of error and the code associated with that type.

ICMP Error Message Structure

ICMP messages typically have the following header fields:

Type (8 bits): Indicates the type of the message (e.g., error message or echo request).
Code (8 bits): Provides additional context for the type (gives more specific information about the error).
Checksum (16 bits): Used for error-checking the header and data.
Unused (32 bits): Usually set to zero, used in some ICMP types for future use.
Identifier (16 bits): An identifier used for matching requests with replies (used in echo requests/replies).
Sequence Number (16 bits): A sequence number for the echo requests/replies to track multiple messages (used in echo requests/replies).

Specific Example

For the ICMP message type you provided:

Type = 3: This indicates Destination Unreachable, which is the type of the ICMP message.
Code = 0: This indicates Network Unreachable.

The Type and Code together can help pinpoint exactly what the issue is within the broader category of destination unreachable messages.

ICMP Error Handling Table (Detailed)

Here’s the modified error handling table with specified headers, illustrating the connection between Type and Code:

ICMP Type	ICMP Code	Meaning	Recommended Action
3	0	Network Unreachable	Check routing configuration
3	1	Host Unreachable	Verify that the target host is operational
3	2	Protocol Unreachable	Check routing configuration or application protocol support
3	3	Port Unreachable	Ensure that the service is running on the target
11	0	Time to Live Exceeded	Examine routing paths for loops
11	1	Fragment Reassembly Time Exceeded	Investigate maximum transmission unit (MTU) settings

Summary

3: ICMP Type for “Destination Unreachable”
0: ICMP Code for “Network Unreachable”

This table provides a clear understanding of the relationship between ICMP types and codes, helping network engineers and administrators troubleshoot issues effectively.

ICMP Queries Table

ICMP Type	Description	Common Tools	Example Command
8	Echo Request	`ping`	`ping [destination]`
0	Echo Reply	`ping`	(Automatically received upon ping)
13	Timestamp Request	Custom Tools	`ping -t [destination]` (with timestamp option)
14	Timestamp Reply	Custom Tools	(Automatically received upon timestamp request)

Key Characteristics

Transport Protocol: ICMP operates at the network layer (Layer 3) of the OSI model.
Connectionless: It does not establish a connection before sending messages.
Error Handling: Allows hosts to communicate error and status information back to the sender.

Ping (Echo Request):
- To check the reachability of a host:
```
ping [hostname or IP]
```

Traceroute (Trace Route):

To track the path packets take to reach a destination:

traceroute [hostname or IP]  (Linux/Unix)

tracert [hostname or IP]  (Windows)

This cheat sheet summarizes the key aspects of ICMP, including its function, types, error handling, and common queries. The tabular format provides easy reference to critical information, making it straightforward to understand ICMP’s role in network communications.