All language subtitles for 9. Local Loopback Address

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