Some network protocols can be used as a way to attack networks and you should understand how they work
to enhance your cybersecurity abilities ICMP is one of the most well-known protocols and is widely used
for network monitoring and discovery ICMP requests also known as pings can be sent to a network host
or range of IP addresses to verify connectivity.
Hackers can maliciously use the ICMP protocol for reconnaissance and denial of service attacks known
as ICMP floods.
So even though the ICMP protocol is very useful for troubleshooting and monitoring to prevent this protocol
from helping attackers it should be blocked on internet adds devices.
Pings can be sent from any network device
by using the command P and then your destination IP address or hostname.
You can verify now were connectivity.
So here for my computer I'm pinging my default gateway routers IP address.
And here I can see that my ping was successful and I received ICMP replies from the destination host.
If you were to ping something that was unreachable on your network you would get request time.
As you can see here the destination IP address I am sending a ICMP request to is not reachable on the
network.
So I'm getting a request timed out so you can see a packet capture of an ICMP request in response.
I have wireshark running filtered to only capture ICMP messages and I'm going to just ping something
on the Internet
beacon see pretty simple my source IP address is sending a ping request to my destination IP and then
they're responding with a Ping reply which is what we're seeing here in our command line output in the
next video we're going to talk about.
R which maps layer to to layer 3 addresses for IP version 4 addresses or doesn't feel right to and the
ICMP video without talking about ICMP version 6 which is used for Layer 2 to layer 3 mappings for IP
version 6 addressing.
So just like learn the next video when hosts need to communicate to other host something not work or
routers they need layer 2 and layer 3 information by default of a host wants to communicate with a network
device it knows what the destination layer 3 address is going to be.
The hard part is how to figure out what the layer 2 addresses for its destination.
Earlier in this course we talked about MAC addresses which are the layer 2 addresses on networking devices
with IP version 6.
This is referenced as being the link layer address and host need to discover their neighbors link layer
addresses so they can communicate with them and that's what brings me back to ICMP.
Version 6 ICMP version 6 messages can be sent between hosts to help discover link layer address saying
among other things you're really not expected to know anything about IP version 6 for the exam but you
should at least know about ICMP version 6 and how it can be used to discover link layer addresses.
OK in the next video you'll learn how IPV for hosts learn the same type of layer to layer 3 mapping
but instead using the ARP network protocol.