IP has no mechanism for error reporting or error-correcting. ICMPv4 was created to overcome this. a) What is ICMPv4? b) How do we use ICMPv4 with the TCP/IP Suite? c) How does it overcome the limitations in IP? Solution What is ICMP? ICMP stands for Internet Control Message Protocol. It is an error reporting protocol network device like routers used to generate error messages to the source IP addresses when network problem prevent delivery of IP Packets. ICMP creates and sends messages to the source IP address indicating that a gateway to the router, host and service cannot be reached for packet delivery. Any Network IP device has the capability to send, receive or process ICMP messages. How do we use ICMPv4 with the TCP/IP Suite? Various message types are defined in ICMP that allow different types of information to be exchanged. These are usually either generated for the purpose of reporting errors, or for exchanging important information of different sorts that is needed to keep IP operating smoothly. ICMP itself doesn\'t define how all the different ICMP messages are used; this is done by the protocols that use the messages. In this manner, ICMP describes a simple message-passing service to other protocols. ICMP is not like most other TCP/IP protocols in that it does not perform a specific task. It defines a mechanism by which various control messages can be transmitted and received to implement a variety of functions. ICMP is considered an integral part of IP, even though it uses IP to sends its messages. The operation of ICMP involves some portion of the TCP/IP protocol software on a machine detecting a condition that causes it to generate an ICMP message. This is often the IP layer itself, though it may be some other part of the software. The message is then encapsulated and transmitted like any other TCP/IP message, and is given no special treatment compared to other IP datagrams. The message is sent over the internetwork to the IP layer at the receiving device. Again, since many of the ICMP messages are actually intended to convey information to a device\'s IP software, the IP layer itself may be the “ultimate destination” of an ICMP message once a recipient gets it. In other cases, the ultimate destination may be some other part of the TCP/IP protocol software, which is determined by the type of message received. ICMP does not use ports like UDP or TCP to direct its messages to different applications on a host; the software recognizes the message type and directs it accordingly within the software How does it overcome the limitation in IP? IP is an unreliable method for the delivery of network data. It is known as a best effort delivery mechanism. It has no built-in process to ensure that data is delivered. If an intermediary device such as a router fails, data cannot be delivered. Additionally, nothing in its basic design allows IP to notify the sender that a data transmission has failed. ICMP is the component of the TCP/IP protocol.

1. IP has no mechanism for error reporting or error-correcting. ICMPv4 was created to overcome
this.
a) What is ICMPv4?
b) How do we use ICMPv4 with the TCP/IP Suite?
c) How does it overcome the limitations in IP?
Solution
What is ICMP?
ICMP stands for Internet Control Message Protocol. It is an error reporting protocol network
device like routers used to generate error messages to the source IP addresses when network
problem prevent delivery of IP Packets. ICMP creates and sends messages to the source IP
address indicating that a gateway to the router, host and service cannot be reached for packet
delivery. Any Network IP device has the capability to send, receive or process ICMP messages.
How do we use ICMPv4 with the TCP/IP Suite?
Various message types are defined in ICMP that allow different types of information to be
exchanged. These are usually either generated for the purpose of reporting errors, or for
exchanging important information of different sorts that is needed to keep IP operating smoothly.
ICMP itself doesn't define how all the different ICMP messages are used; this is done by the
protocols that use the messages. In this manner, ICMP describes a simple message-passing
service to other protocols.
ICMP is not like most other TCP/IP protocols in that it does not perform a specific task. It
defines a mechanism by which various control messages can be transmitted and received to
implement a variety of functions.
ICMP is considered an integral part of IP, even though it uses IP to sends its messages. The
operation of ICMP involves some portion of the TCP/IP protocol software on a machine
detecting a condition that causes it to generate an ICMP message. This is often the IP layer itself,
though it may be some other part of the software. The message is then encapsulated and
transmitted like any other TCP/IP message, and is given no special treatment compared to other
IP datagrams. The message is sent over the internetwork to the IP layer at the receiving device.
Again, since many of the ICMP messages are actually intended to convey information to a
device's IP software, the IP layer itself may be the “ultimate destination” of an ICMP message
once a recipient gets it. In other cases, the ultimate destination may be some other part of the
TCP/IP protocol software, which is determined by the type of message received. ICMP does not
use ports like UDP or TCP to direct its messages to different applications on a host; the software

2. recognizes the message type and directs it accordingly within the software
How does it overcome the limitation in IP?
IP is an unreliable method for the delivery of network data. It is known as a best effort delivery
mechanism. It has no built-in process to ensure that data is delivered.
If an intermediary device such as a router fails, data cannot be delivered. Additionally, nothing in
its basic design allows IP to notify the sender that a data transmission has failed. ICMP is the
component of the TCP/IP protocol stack that addresses this basic limitation of IP.
ICMP does not overcome the unreliability issues in IP. Reliability is provided by upper layer
protocols.
When datagram delivery errors occur, ICMP is used to report these errors back to the source of
the datagram. ICMP does not correct any network problems that it encounters, it only reports
them. ICMP reports on the status of the delivered packet only to the source device. It does not
send information about network changes to other routers.
Difference in Message Delivery of ICMP and IP :
ICMP messages are encapsulated into datagrams in the same way any other data is delivered
when IP is used. Since ICMP messages are transmitted in the same way as any other data, they
are subject to the same delivery failures. This creates a scenario where error reports could
generate more error reports and cause increased congestion on a network. For this reason, errors
created by ICMP messages do not generate their own ICMP messages. Therefore, it is possible
to have a datagram delivery error that is never reported back to the sender of the data.
ECHO messages used by ICMP:
Echo messages generally starts with PING command to check the destination reachability. All
ICMP message formats start with the same three fields:
The type field indicates the type of ICMP message being sent. The code field includes further
information specific to the message type. The checksum field, as in other types of packets, is
used to verify the integrity of the data.
Importance of ICMP while sending Control messages:
The reasons for this are simple. Since IP does not guarantee delivery, it cannot inform hosts
when errors occur. Second, IP has no built-in method to provide control messages to hosts.
Control messages are used to inform hosts of conditions such as network congestion or the
existence of a better gateway to a remote network. ICMP uses the basic IP header to travel
through multiple networks.