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7. IP Addressing – Part 2

7. IP Addressing – Part 2

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IP Addressing – Part 2 – Transcript:

Network Mask

Every ip device having address works inside some network segment. This segment has also own address called netwrok address. All devices having addresses within the network address in the range. To specify the range of addresses in particular network some kind of delimiter is needed and this is network mask. Look at the given example: we have IP address of and mask of , logical and between address and maks gives us the network address. This excelent example for binary notation bacues the and is between bits of address and bits of mask in the same order. 1 and 1 give 1 , 1 and 0 gives logicaly 0. Thus the network address after the logical multiplication is and this is address of netowkr that describes whole range of IP space for given subnets. Out is of course within the range

Network Mask 2

In networking the mask is inherent of the address. The notation of mask can be full dotted decimal or just the numer of ones counting from the left of the mask. So 16 is the numer of ones from the left of the mask.


Lets take look at the example. Tha network address is the mask is 16. From those factors we can designate the network portion and host portion. Network portion is portion of ip address that is on the left side of mask . The host portion is the right side of mask.  Host porition is the addressing space for host withing partciular network. In our example the host portion is 16 bit tha makes 2 ttp of 16 addresses. This means that for /16 network we have space for 65535 addresses.

Network Mask Example 2

In another examle we have mask of 24 bits. Counting from the left we have 8 bit space left for the hosts space. Tha makes 2 ttp 8 256 potential addresses. However not all addresses from the space can be used for devices.

Addressing Design Network Host

Now if you now the crucial terms like address space, network adderss and network mask we can take a look at the addressing planning subjecct. Given following topology we can see network devided by router to 3 networks segments. Netwok A has address space for 256 addresses but there only 3 host inside, networks B and C have also  /24 mask so 256 addressgin space. This might sometimes not optimal to loose the address. Lets Focus on addressing optimization, usable addresses counting.

Usable Addresses

When having 24 bit mask we have 1 octet free for host space. Hta makes 2 ttp of 8 possibilites so its 256 but first possible address is always reserved for the network address itself, in our case first address will be and this is network address or sometimes called network prefix. Last address within the network is reserver for broadcast used typically in one to any communication. So usable address for devices are from 1 to 254. You can also make quick formula from described rule. Usable addreses for host equals space – 2. one for network and one for bcasty.

Addressing Example 1

Having example lets try to count yourself. 192….

Addressing Example 2

And again example numer 2.

Classful Networks

In 1981 there was an efort of systemize addressing scheme. The introuduction of Classull network defined the address ranges that fit into particular address class. There were 5 classes class, a,b,c,d,e. The mask length had only 3 options: 8 bits for class a, 16 bits for class b and 24 bits for class c. class d was used for multicast type of traffic only and class e was reserved for special purpose. If you had to address your private network you had to use addresses from class a b or c with specified mask.

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