Subentting, Supernetting and VLSM presentation on Networking.

1. Welcome to presentation
on Subnetting,
Supernetting, VLSM

2. Classfull Addressing
• IP addresses, when started a few decades
ago, used the concept of classes.
• This architecture is called classful
addressing.

3. Type of Classes and ranges
• Class A = 0 - 127
• Class B = 128 - 191
• Class C = 192 - 223
• Class D = 224 - 239
• Class E = 240 - ∞

4. Subnet Mask
• Subnet mask is a 32 bits long address used to
distinguish between network address and host address
in IP address.
• For example how will we figure out network partition
and host partition from IP address 192.168.1.10 ?
Here we need subnet mask to get details about
network address and host address.

5. In decimal notation
• In decimal notation subnet mask value 1 to 255
represent network address and value 0 [Zero]
represent host address.
IP address 192.168.1.10
Subnet mask 255.255.255.0
• Network address is 192.168.1 and host address
is 10.

6. In binary notation
• In binary notation subnet mask ON bit [ 1] represent
network address while OFF bit[0] represent host
address.
IP address
11000000.10101000.00000001.00001010
Subnet mask
11111111.11111111.11111111.00000000
• Network address is 11000000.10101000.00000001
and host address is 00001010

7. Supernetting
• Supernetting is the opposite of subnetting
• In subnetting you borrow bits from the host
part
• Supernetting is done by borrowing bits from
the network side.
• And combine a group of networks into one
large supernetwork.

8. Example
• A company needs 600 addresses. Which of the
following set of class C blocks can be used to form a
supernet for this company?
• 1. 198.47.32.0 198.47.33.0198.47.34.0
• 2. 198.47.32.0198.47.42.0 198.47.52.0 198.47.62.0
• 3. 198.47.31.0198.47.32.0 198.47.33.0 198.47.34.0
• 4. 198.47.32.0 198.47.33.0 198.47.34.0 198.47.35.0

9. Solution
• 1: No, there are only three blocks.
• 2: No, the blocks are not contiguous.
• 3: No, 31 in the first block is not divisible by 4.
• 4: Yes, all three requirements are fulfilled.

10. CIDR
• Classless Inter Domain Routing
• CIDR is a way to allow more flexible
allocation of Internet Protocol (IP) addresses
than was possible with the original system of
IP address classes.

11. CIDR representation
a.b.c.d/n
(like: 192.168.10.1/27)

12. Rules of CIDR blocks
• All IP address are should be contiguous
• Block size always 2n
• First IP addrees in the block should be evenly
divisable by size of the block

13. VLSM
• VLSM: Variable Length Subnet
Masking.
• Any prefix length is allowed in the
network at any point.
• Q: You have 4 subnets with the
following numbers of hosts: 58, 29,
14, 3 and the address is
192.168.10.0/24
• Determine what subnets you could
use to fit these hosts into it and the
address.
10.1.1.0/24
10.1.2.0/25
10.1.2.128/26
10.1.2.192/27
All of these are valid
in the same network!

14. Working with VLSM
• We have 58, 29, 14, 3 Hosts.
Start with 58.
• Smallest number larger than
(58+2) is 64. 64 is 2 bits.
• 24 bits of prefix length in the
address space given, add 2 for
26.
• First network is 192.168.10.0/26.
• The next network is
192.168.10.0+64, so we start the
next “round” at 192.168.10.64
8 7 6 5 4 3 2 1
1 2 4 8 16 32 64 128
32 < (58+2) < 64
So, 192.168.10.0/26 takes
care of the first 58 hosts
24 + 2 = 26
Start the next block at
192.168.10.64

15. Working with VLSM
• Now this block has 29 hosts.
• Smallest number larger than
(29+2) is 32. 32 is 3 bits.
• 24 bits of prefix length in the
address space given, add 3 for
27.
• We start this block at
192.168.10.64, so network is
10.1.1.64/27
• The next network is
192.168.10.64+32, so we start
the next “round” at
192.168.10.96
8 7 6 5 4 3 2 1
1 2 4 8 16 32 64 128
16 < (29+2) < 32
So, 10.1.1.64/27 takes care
of the first 29 hosts
24 + 3 = 27
Start the next block at
10.1.1.96

16. Working with VLSM
So, the subnets for -
58 host: 192.168.10.0/26
29 host: 192.168.10.64/27
14 host: 192.168.10.96/28
3 host: 192.168.10.112/29

17. Any Question...

18. Zakaria
Hossain