ICMP in Cisco packet tracer and how it is used?

What is the role of ICMP in Cisco packet tracer and how it can be used for testing and troubleshooting?

Internet control message protocol is used to check the connectivity within the network. ICMP is one of those protocols used most often by network administrators while troubleshooting network issues.

In the Cisco packet tracer, the ICMP protocol request is sent to the destination when we use the ping command and if the proper connectivity is established then we will get the ICMP reply back from the destination address.

While creating a network in the packet tracer, it is essential to check the connectivity at every step because it is easy to find our issue at the earliest otherwise, it becomes hard if we have already created the network and there is no proper connectivity.

Ping command is supported by most of the devices in packet tracer so we can use this command in various types of devices added to the network.

We can also enable the simulation mode in the packet tracer while pinging other devices to see how the ICMP traffic travels in the network. If any device is not sending the ping replies then we can see which address is giving us a reply back and that can help us to troubleshoot the network.

 

Check the above image to see how the simulation mode track packets at every step. We have generated the ICMP traffic to test and you can see the ICMP packets captured in this mode.

Traffic generator can also be used in a packet tracer to generate ICMP traffic. This generator is helpful while experimenting with different types of traffic.

ICMP traffic can be blocked in packet tracer using the standard and extended access list.

To use the ICMP protocol, we must have the IP address assigned to the source and destination as ICMP protocol uses an IP address to travel in the network.

In the real world, many companies block ICMP traffic as this poses the threat to security. In a highly secured environment, firewalls are used to block any unnecessary traffic to the servers or other devices.

When the ICMP is blocked then we see request timed out error on the computer screen. Although the destination is receiving the ICMP traffic, however, they are denied sending the replies back to the source. Access list, firewall, and other high-security devices can be configured to drop the traffic from the unknown source however; it may be possible that the ICMP traffic is allowed within the local area network.

As ICMP traffic usually uses very small size of packets, it does not overload the network and does not overload the network resources.

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