welcome back in a recent video we discussed how addresses are important devices need them so they
know where to send their data IP addressing is a good example of this not only does it include
the address of the device but the address of the network that the device is in that means with one
simple address we can find a device on our local network or on the other side of the world IP
addresses come in two different flavors these are called ipv4 and ipv6 and they look quite different
ipv6 is newer but ipv4 is still more common so we're going to focus our attention entirely on
ipv4 for now firstly this is what an IP address looks like it's four numbers separated by dots
each of these numbers is called an octet as each number is an 8-bit value we break it up into four
separate octet to make it easier for us humans oh and if you're having trouble remembering one
octet is think of an octopus an octopus is eight tentacles and octet has eight bits eight bits
means that these numbers can range from 0 to 255 that means that an IP address starts at 0 0 0 0
and ends at 255 dot 255 dot 255 dot 255 we call a range of addresses the IP space straight away you
can see that knowing how binary works is important for IP addressing if you don't know a binary or if
you need a refresher I have a video to help I'll add it to the description IP addresses
are actually two addresses in one the IP address is the address of the device but it's also the
address of the network that the device is in two addresses in one how is this possible let's take a
look at this sample IP address here 172 dot 16 dot 0 dot 1 the first part 1 7 2 dot 16 refers to the
network the second part 0.1 is the host address don't worry I'll get to explaining how we know the
difference between the two soon all the hosts here that start with 1:7 2.16 are in the same network
if we add more hosts and the IP addresses start with 1:7 2.17 then this is a different network if
hosts in different IP networks need to communicate then then we'll need to be a router between them
you're probably wondering is it always the first half of the address that represents the network
short answer no how then do we know which part of the IP addresses the network and which part
is the host the answer to this question strangely has changed over time so let's start back at the
beginning and we'll work along from there when the Internet Protocol was first created the
first octet always represented the network and the following three octet were used for hosts
the largest value that we can get out of a single octet is 255 that means that there was only room
for 255 different networks on the other hand three octets meant that there could be over 16 million
hosts IPS in each network this sounds a little unbalanced but in the beginning the internet
was not international and there were only a few organizations using it but as the internet started
to grow it became obvious that this wouldn't work for very long 255 networks just wasn't enough so
back in 1981 a new method was introduced this broke the entire IP space into five classes
that's Class A through to E Class A B and C were used to address devices Class D is for multicast
and we'll touch on that a little in the next video Class E is reserved for special purposes so Class
A B and C are the ones we need to think about right now there are a small number of Class A
networks but each network supports a large number of hosts Class A works a bit like the old method
the first octet is the network and the remaining three octet are for hosts however the first bit of
the network is always 0 that leaves seven bits for us to allocate to our networks that means there
are 128 Class A networks with more than 16 million host IPS per Network the Class A address base then
is 0.000 through to one 27000 there is a small catch with this though networks starting with 0
and 127 are reserved so the usable class a space is really 1.000 to 120 6.000 Class B networks are
used for a medium number of hosts the first two octets are used for the network and the second
two are used for host addresses the first two bits of the network are always 1 0 which leaves 14 bits
or 16384 possible networks each network can have over 65,000 hosts the total Class B IP space is
from 1 28000 to 191 to 5500 Class C are small networks but there are a lot of them the first
3 octets are just for the network the first three bits are always 1 1 0 leaving 21 Network bits or
a little over 2 million networks with only 1 octet left though we can have only 256 hosts
ip's per Class C Network the address space ranges from 190 to 0 0 0 2 223 255 255 0 so to summarize
Class A uses 1 octet - 1 bit for networks Class B uses two octets - 2 bits and finally Class C uses
3 octet - 3 bits addresses outside of this our classes D and E which are reserved for special
uses if you're the kind of person that likes the math we can show this as an equation the number of
networks is 2 to the power of n and is the number of network bits so Class B has 14 network bits to
the power of 14 years 16384 the same is true for hosts B has 16 bits four hosts two to the power
of 16 is about 65,000 ready for some practice take a look at these IP addresses which classes
are they in time to look at an example if device 170 2.16 dot zero dot one wants to send a packet
to 172 1602 it starts by looking at the first few bits of the destination IP address as the first
two bits are 1 0 it knows that this is a Class B address it can then assume that the first 2 octet
are the network and the last two are the host it sees that the destination network is 172 dot
16 which is the same as its own as they're in the same network it can send traffic directly
to the destination now what if it wants to send a packet to 172 dot 17.0 to 1 it does the same
thing and it determines that the destination is on the 170 2.17 network this is different to its
own network so it can't send traffic directly it needs to send traffic to a router first take the
practice session from before a step further tell me which part of each address is the host address
as the internet started to grow we started using up IP addresses faster and faster and we started
running low on IP addresses again so in 1993 yet another new method was introduced it is called
classless inter-domain routing or cider previously we could identify IP address class by looking at
the first few bits knowing the class we then knew which parts of the IP were for the network and
which parts were for the hosts but now we throw all that away and we introduce something new the
subnet mask the subnet mask is also made up of four octet s-- this lines up with the IP address
bit for bit the bits set to one tell us which part of the IP address is the network the zero bits are
used for hosts it's important to notice that all the ones go on the left and all the zeros go on
the right we never mix up the ones and zeros in a subnet mask take a Class A address for an example
we know eight bits are used in the network so the subnet mask would look like this eight one
bits for the network the remaining 24 bits set to zero for hosts a Class B address follows the same
rules sixteen bits for the network set to 1 and the host bits set to zero and finally Class C well
you get the idea by now is this making sense so far the subnet mask tells us which part of
the IP is for the network and which party's for the hosts but this hasn't really addressed our
original problem yet has it so far we've just seen a different way to show Class A B and C
addresses so far we haven't seen anything on how to save IP addresses the real power of cider is
the ability to break a large network into small ones we call this subnetting let's say that you
have the classful network of 170 to 1600 this would have the subnet mask of 255 255 0 0 this
allows for about 65,000 hosts that's a lot of hosts that might be fine if we have one massive
office but what if we have several smaller offices do we want to allocate 65,000 IPS to each office
that seems like overkill to me so instead what we can do is we can break the Class B Network using
our subnet mask we may decide to use 255 255 255 dot 0 instead now our large office network has
been broken into 256 different subnets why 256 well our subnet mask is now using an additional
8 bits for the network the largest 8-bit value is 256 now we can allocate 256 host IPS per network
which is far more reasonable when we have a few small offices if we want to communicate between
our subnets just like before we will need a router let me take a moment to make sure that I'm clear
on this devices in the same subnet must be in the same IP network if not they will not be able
to communicate likewise if devices in the same subnet are separated by a router they will also
not be able to communicate I'd like to challenge you to think this through for yourself take the
172 dot 1600 network with a subnet mask 255 255 0 0 if we broke that network up by using the subnet
mask of 255 255 to 40.0 how many subnets do we have how many host IPS per subnet are there
if you're taking notes you've probably noticed that's a pain to write down the subnet masks all
the time to make things simple we have what's known as cider notation take 1 7 2 dot 16 dot
one dot 0 / 24 as an example the slash 24 is the subnet mask written inside a notation this means
that the first 24 bits of the subnet mask are turned on it's that easy we will be using side
of notation more and more from here on so try to get more comfortable with it see if you understand
by testing yourself with this example we have to slash 24 networks these are joined together by a
small slash 30 network a device in network a is unable to communicate with a device in network
B why are they unable to communicate classful is an older method of networking and subnetting is
newer so why are we even talking about classful networking hasn't it been replaced yes it has
been replaced but for one if you're doing an exam you may still find exam questions that refer to
class for addressing we also have some remnants of classes in everyday networking think of when
you set an IP address in Windows for example if you configure an IP of 10.8 62 windows will
automatically give you the subnet to 55000 it's assuming classful networking and what we're mostly
classless now a lot of people tend to think of subnetting are starting with a classful network
and breaking it up from there which is not always strictly true sometimes we may have a few small
networks and we decide to join them together this is called super netting for example it may have
one nine two one six eight zero zero slash 24 and one nine two one six eight one zero slash
24 if we want we can join these into a single network 192.168.0.0 slash twenty-three in my
opinion we shouldn't really worry about class all networks in the real world use subnetting
all the way but what do you think tell me if you agree or disagree in the comments I would
love to hear your opinion join me the next video and we'll dive deeper into IP addressing concepts