🔻The Internet Control Message Protocol (ICMP) is a network layer protocol used by network devices to diagnose network communication issues.
🔻ICMP is mainly used to determine whether or not data is reaching its intended destination in a timely manner.
🔻Internet Control Message Protocol (ICMP) is a layer 3, Network Layer protocol.
🔻Internet Protocol (IP) provides connectionless datagram delivery.
📌error-reporting and error-correcting mechanism.
🔻ICMP provides a way to handle errors in data transmission.
🔻It is also used for network diagnostics.
📌ICMP only reports error, error correction is done by higher layer protocols.
🔻It always reports errors to the original source/sender.
🔻ICMP messages are broadly divided
into two types:
📌 1. Error reporting messages
📌 2. Query messages
🔻Error reporting messages reports problem that a router or host encounters while processing IP packet.
🔻Query messages are used to get routing information in a network. It helps the host to get the specific information about another host.
🎯🔶ICMP can handle following types of errors:
🔻1. Destination Unreachable
🔻2. Source quench
🔻3. Time exceeded
🔻4. Parameter Problems
🔻5. Redirection
📌🔶1. Destination Unreachable:
🔻This error occurs when packet does not reach to the destination.
🔻 When a router is not able to route the packet to the destination, it discard the packet and sends destination unreachable message to original source.
🔻This message is either generated by router or by the destination host.
📌🔶2. Source Quench:
🔻IP does not provide any flow control or congestion control mechanism. Sender only sends data without knowing the receiving capacity of destination.
🔻Also it never knows if router or destination host has been flooded by packets.
🔻This may create congestion in network.
🔻When a router or destination host is not able to receive packets on the speed as they are sent by sender, it simply discards packets due to congestion.
🔻Then it sends source quench message to original sender. The sender then decrease the data transmission speed.
🔻When a congestion router is far away from original source, the ICMP sends source quench message hop by hop so that each intermediate hop may slow down the speed.
📌🔶3. Time Exceeded:
🔻Sometimes it may happen that a network consists of many routers.
🔻If any of the routers fail to locate next hop then a packet may route in a loop.
🔻This looping may cause TTL value reach to 0.
🔻When TTL value reaches to 0, the data packet is discarded by router and time exceeded message is sent to original sender.
🔻This message is also generated when destination has not received all fragments of one IP packet in certain time.
🔶📌4. Parameter Problem:
This message is generated when router or destination host finds some incorrect or missing information in IP packet.
🔶📌5. Redirection:
🔻This message is sent by router to sender to notify about best available route for transmission when number of routing paths are available between source & destination.
🔻Router may also change the path if congestion occurs in a network.
🔻Then it notifies the sender about changed path.
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