Question

explain the importance of internet control management protocol (ICMP) in delivery of internet protocol (IP) best-effort service and discuss the categories of icmp message.

Answer 1

Solution:

Part 1:

ICMP stands for Internet Control Message Protocol. It is a network layer protocol but its messages are not directly passed to the Data Link Layer .Instead the messages are encapsulated in a IP datagram before going to the lower layer. It is designed to overcome the following two problems of Internet Protocol :

(1) No Error Reporting/ Correctness Mechanism

(2) Lacks a mechanism for Queries.

Since the IP protocol has no error reporting or error correcting mechanism . . So if a router or host sends a packet acroos routers and there occurs an error which causes the packet to be lost in between . The sender will assume that the packet has been received. So the sent packet is lost.This is why IP is a best-effort service So to inform the sender about the status of the packet IP uses ICMP protocol to send messages between routers or host at network layer. Given below is a diagram of position of ICMP in Network Layer. Best-effor service

Part 2:

There are two different types of messages produced by ICMP , one is for Error Reporting and other is for handling the Query known as ICMP Query messages

Error Reporting : The Error Reporting messages report problem that the Router or Host may encounter while processing of IP packet. ICMP reports error message to the original source. ICMP does not correct errors. Below we see the types of error reporting messages.

1) Destination Unreachable : Whenever a Route to the destination is not found , datagram is discarded and Router/Host sends Destination Unreachable message back to the source.

2) Source Quench : This message informs the Source that a datagram has been discarded due to congestion.

3) Time Exceeded : This message is generated in the follwoing cases :

Case 1: Whenever a Router decrements a datagram with Time To Live(TTL) value to zero it discards the datagram and sends a time exceeded message to original source.

Case 2: When the final destination doesn't all fragments in a set time, it discards the received fragments and sends a time-exceeded message to the priginal source.

4) Parameter Problem : If router /host discovers an ambiguous or missing value in any field of the datagram , it discards datagram and sends a Parameter Problem message back to the source.

5) Redirection:  It is sent from a router to a host on same local Network. To understand this look at the diagram below:

Here R1,R2 are routers and A and B are host. Suppose wants to send a packet to B . So the shortest path would be via R2 but it sends it to R1 . Now R1 checks its routing table and sends it to R2. And also sends a redirection message to source that is A so that A knows that the packet is sent to B through R2.

ICMP Query Messages : Query messages are used to fetch important or specific messages from a router or host. It is used to dianose some network problems .The different types of ICMP query messages are:

1) Echo Request and Reply : Designed for diagnostic purpose These message are used to determine whether two systems can comunicate with each other. Here is a diagram where A and B are two systems or two hosts.

Echo Request and Reply

  

2) Timestamp Request And Reply : Two machines uses these messages to determine the Round Trip time needed for a IP datagram to travel between them.

So these are the types of messages in a ICM protocol.

Hope you understood the answer. For any queries please write in the comment section.