Another special type of address is the Local Loopback Address
which is very useful for testing, a device can send a message
to itself and this helps verify or make sure that
the TCP/IP stack is installed correctly on that machine
A typical Loopback IP Address is 127.0.0.1 but remember please
that anything in the 127 range is deemed a Loopback Address
This is often seen as one of the big mistakes by the designers
of IPv4, a 127 address is a Class A Address
Class A Addresses have 16 million odd host addresses
and by chossing this address range for the Loopback Address
we lost the use of potentially 16 million IP Addresses
Host Addresses cannot be allocated as Public IP Addresses
on the Internet thus making the IPv4 Address space smaller than
it may have been, in IPv6 a different addresses used for the
loopback ::1 and they made sure that they didn't make
the same mistake again
So here's an example, I can type ipconfig on my PC
and this will give me the IP Address of my machine
In this example it's 10.0.0.6 that's the Local IPv4 Address
on my PC, so I could ping 10.0.0.6
and as you can see the ping succeeds
I can also however ping my Loopback Address
So I could ping 127.0.0.1
and notice the ping also succeeds
but don't forget anything in this ranges supported
so 127.127.127.127 is also a Loopback Address
What about 127.1.2.3?
it also works, so anything in the range 127.x.x.x
is also a Loopback Address and anyone of those addresses
could be used to test the TCP/IP Stack
Now this machine has both IPv4 and IPv6 installed
So here's my PC's IPv6 Address
So I could ping 2001:20::2 which is my Local PCs IP Address
but I could also ping ::1 which is my IPv6 Loopback Address
Now this video doesn't discuss IPv6 in any detail
But it's worth fighting out that we have both an IPv4 Loopback
such as 127.0.0.1 as well as an IPv6 Loopback such as ::1
IPv6 Addresses are not wasted or to be more politically correct
IPv6 Addresses are optimized more than they are in IPv4
Please also note that routers and switches
also have Loopback Addresses and that's not the same concept
as the Loopback Address that we're discussing here
So be aware that in the field or in the real world
Engineers will often refer to a routers Loopback Address
and that's not the same as what we're discussing here
You've got the Local Loopback which is the Class A Address
127.0.0.1 but routers and switches can also be configured
with valid IP Addresses on what's called a Loopback interface
So a router or switch may have a Loopback Interface such as
Interface Loopback 0, configured with an IP Address
of 10.1.1.1/32, so in other words we have a Class A Address
10.1.1.1 with a /32 mask configured on a Loopback Interface
but Network Engineers may refer to the router's Loopback
IP Address and they are referring to this IP Address
and not 127.0.0.1, I will explain as I've mentioned in a moment
what a Network mask does but what I'd like to point out here
is that routers and switches have separate Loopback Addresses
which are different to the Local Loopback Address
that we're discussing now, routers and switches do support the
Loopback Address of 127.x.x.x which allows us to verify
the TCP/IP Stack but Loopback interfaces
on routers and switches are very useful for other things
and are used by routing protocols such as OSPF