IP Address Classes and Subnet Mask: Network vs Host Portions Explained

welcome to the part two of class full addressing we will start with the outcomes in today's session we have

three outcomes let's see what are they upon the completion of this session the learner will be able to outcome number

one we will recall the various classes of ipv4 address outcome number two we will understand the purpose of subnet

mask and outcome number three we will identify whether the nodes belonging to the same network or different network

let's recall the various classes of ipv4 address we know basically there are five classes of ipv4 address class a b c d

and e and we know ipv4 addresses have four octane and if the first octet is between 0 and 127 it is obviously class

a if it is between 128 and 191 it is class b if it is between 192 and 223 it is class c

if it is between 224 and 239 it is class d class d addresses are multicast addresses

and if the first octet of ipv4 is between 240 and 255 then it is class e class e is for experimental and research

purpose and we have already seen what is this in the previous lecture now i am going to introduce a very important term

called the subnet mask ip addresses are just the identity of the device in the network if i say there is a device with

ip address 10.5.6.8 we don't know more about the network with the help of ip address we can just

know what is the identity of the device but if we want to know who are all in the network then ip addresses must be

accompanied with another parameter and that parameter is the subnet mask this subnet mask will be usually accompanied

by an ip address and this subnet mask only says who are all in the network ip address says what's the identity of a

device in the network subnet mask says who are all our neighbors in the network in a classful

world of ipv4 address class a class b and class c are accompanied with the subnet mask that is the default subnet

mask i already told you that class a b and c are mainly for general purpose that we can use for our computers

we have public ip addresses and private ip addresses falling in the class a b and c i'm not going to talk about that

public and private ip addresses in this lecture let's just have these classes that is class a b and c are general

purpose ip addresses class d addresses are multicast addresses and class e is for experimental and even research

purpose in a classful world class esip address will always be accompanied with the

default mask which is 255.0.0.0 so 255 means all bits are one right all bits are won in the first octet whenever

all bits are won in the first octet in binary in other words whenever there is a 255 in an octet it means that is the

network portion so in class a the default mask the default subnet mask this is the default subnet mask in

decimal if the default subnet mask is 255.0.0.0 it means this is class a subnet mask so

when it is 255.0.0.0 it means the first octet is the network portion then the remaining three octets

are the host portion basically ip addresses contain two important parts one is the network

portion and the other one is the host portion without subnet mask we can't say which is the network portion and which

is the host portion so every ip address is normally accompanied by the subnet mask this subnet mask is required to say

which part is the host portion and which part is the network portion so in this example the first octet alone is the

network portion and the remaining three octets are host version let's take an example class a address which is

10.5.5.6 in this case 10 is the network portion and the remaining octets are host

portion if the first octet matches for any different ip addresses then it do belong to the same network such a big

network it is just see let's take the same class a example that starts with the value 10 so anything that starts

with 10 will do belong to the same network the starting ip address will be 10.0.0.0

and the last the ending ip address will be 10.255.255.250 in class a the first octet can be 0 or 1

or 2 or 3 or up to 127. so a total of 128 networks are possible in class a so such a big

network right so in this network we can have a maximum of one crore 67 lakh 77 214 hosts that are possible per network

that is since only one octet is reserved for the network portion we can have a maximum of two power seven networks

because this octet alone is the network portion how many bits are there in this network portion we have a total of eight

bits because this is the first doctor and we know one bit is reserved right this is for identifying the class so we

can have a maximum of seven bits only so these seven bits only defines the network portion so two power seven

networks that are possible it means 128 networks are possible and in each network how many hosts can be there

we have a total of 32 bits whereas this portion is 8 bit so we are taking this for identifying the class as well as

identifying the network so 8 bits gone so we have remaining 24 bits so these 24 bits that is 2 power 24 host can be

possible per network and out of 2 power 24 host only 2 power 24 minus 2 are usable so always we need to reduce two

ip addresses one is reserved for identifying the network and the other one is for knowing the broadcast address

of that network we will be elaborately dealing about this network address or the network id and the broadcast address

in the classless addressing part for time being you just know the maximum number of host minus 2 will be the

usable host in class a we have lesser number of networks that is 128 networks but where

we have more number of hots in each network coming to class b class b means these two portions will be the network

portion and these two octets will be the host portion so in a class b if there is an ip address the first two octets will

be the network portion and the remaining two octets will be the host portion the default mask for class b in class full

world is 255.255.0.0 so any ip address the first two octet should match because the first

two octets are the network portion and it doesn't care about the next two octets that is the last two octanes so

these last two updates are reserved for hosts so how many networks that are possible we know ip addresses are 32

bits long we have 16 bits here and we have 16 bits here out of these 16 bits we need two bits for identifying the

class because 1 0 is the starting right so this 16 minus 2 which is 14 we have 2 power 14 networks possible in class b

that is 16 384 networks possible and in each network how many hosts can be possible so 2 power 16 2 power 16 is 65

536 where we need to subtract two why one is for the network address another one is

for the broadcast address so 2 power 16 minus 2 will be 65 534 hosts possible per network

that is we can use 65 534 ip addresses when we go for class b let's take a class b address which is

172.15.150.1 so in this case 172.15 should be fixed

any computer that starts with the ip address 172.15 will be belonging to this network why

because the first two octets are network portion let's say there is a computer with 172.100.100.100

and another computer with 172.5.5.5 these two computers do not belong to the same network why the first octet is

matching but not the second octet so when we go for class b the first two octet should match because the default

mask says the first two octet should match and coming to class c the first three portions is the network portion

and the last portion the last octet is the first question so if there is an ip address the first three octet represents

the network and the last octet alone represents the host so in class c the default subnet mask is 255.255.255.0

and these three octet should match and this is only the host portion so this host portion just observed there is only

one octet one octet means eight bits eight bits means the starting value can be zero and the last value can be 255 so

a maximum of 256 values can be possible out of 256 only 254 are usable why the first ip address should be reserved for

the network and the last ip address should be reserved for the broadcast address so out of 256 hosts that are

possible we can use only 254 so how many bits here for host portion it's only 2 power 8 minus 2 and what about the bits

for the number of network the number of bits for network is 24 out of these 24 bits 3 bits are reserved for identifying

the class so 24 minus 3 is 21 so 2 power 21 networks are possible with class c and in each network we can have a

maximum of 254 usable hosts for class d and class e we don't have the default subnet mask let's see more

about the subnet mask this subnet mask can be represented in decimal like this this is for each class

if we convert this into binary we will be having all ones in the first octet and remaining zeros in other three

octane when we go for class b it's two five five two five five zero zero so we'll be having all ones in the first

two octaves and zeros in the next two octets when we go for class c we have all ones that is two five five in first

three octets that is all ones in the first three octane and zero in the last octet so we need not write the subnet

mask as a lengthy one so we can go for a slash notation how many number of ones in this it's

255.0.0.0 for class here right how many ones we have so we have eight ones so we can represent the class a subnet mask as

slash eight for class b subnet mask we have 16 ones so we can represent this as slash 16 so we can represent class c

subnet mask as slash 24 because we have 24 ones here so subnet mask can be represented either in the decimal format

or in the binary format or simply slash notation let's see more about the subnet mask we know ip address will be always

accompanied with the subnet mask let's take an example this example says that the ip address is 192.168.10.10

and we are given with the subnet mask 255.255.255.0 so when the subnet mask is given it says

that three portions are 255 right all bits are one in these three portions or in these three octaves so when these

three octets are 255 so the first three octets in an ip address that is the first three octets in an ip address is

the network portion and the last octet alone is the host portion so any ip address that starts with 192.168.10

they belong to the same network for example if a device is having an ip address 192.168.20

so the device which is having this ip address and the device which is having the ip address

192.168.20. something will not belong to the same network so the communication cannot be established between these two

devices with the help of a switch because a switch is a local area network device it can make communication

possible between the same network or among the devices in the same network if we want to make the communication to

happen for two different networks then a router is needed so in this case any ip that starts with 192.168.10

they do belong to the same network so 192.168 192.168.10.255 is the maximum where

192.168.10.0 cannot be used for the host and similarly the last ip address which is

192.168.10.255 cannot be used it is for broadcast purpose i hope now you can understand the role of subnet mask to

define the network and the host portions of an ip address or simply an address a device use a separate 32-bit pattern

called a subnet mask this subnet mask defines the network portion and the host portion so the subnet mask does not

actually contain the network or the host portion so the subnet mask is not carrying anything with it it doesn't

know what is the network and what is the host with the help of ip address only we can come to know what is the network

portion and what is the host portion so it just says where to look for these portions that is the network portion and

the host portion in a given ipv4 address i hope you are clear with this we have recalled the various classes of ipv4

address we understood the purpose of subnet mask and we identified whether the nodes belonging to the same network

or different network with the help of subnet mask i hope you guys enjoyed the lecture and thank you for watching

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