Subnetting
What was that masked address?
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Subnetting in Computer Network, Schemes and Mind Maps of Computer Networks
**Subnetting Notes – Description** Subnetting is the process of dividing a large IP network into smaller, manageable subnetworks called subnets. It helps improve network performance, enhances security, and ensures efficient utilization of IP addresses. By borrowing bits from the host portion of an IP address, subnetting creates multiple logical networks within a single network. It is commonly used in computer networks to reduce broadcast traffic, simplify network management, and organize devices into separate network segments. Understanding subnet masks, network addresses, broadcast addresses, and host ranges is essential for performing subnetting calculations and designing efficient networks.
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Subnetting
What was that masked address?
IP Address
Unique Identifier (^) 32 bit binary number Represented as 4 decimal values (^) Representing 8 bits, in the range 0 – 255 (known as Octets) Example: 140.179.220. Binary form: 10001100.10110011.11011100.
Why Subnet?
To break the network down into pieces, each of which can be addressed separately. Controls network traffic Reduces broadcasts Can provide low level security with access lists on the router Organization of IP addresses
Subnetting a Default Class C
Network Address: 200.129.41.
Default Class C address is divided into network and host portions as follows: N. N. N. H (^) To subnet we “borrow” bits from the host portion of the address (8 bits for Class C) N. N. N. x x x x x x x x (^) Borrowing n bits yields 2 n^ – 2 subnets. (^) Leaving m bits yields 2 m^ – 2 hosts ( m = 8 - n ) (^) For a class C, we can borrow from 2 to 6 bits.
Subnetting a Default Class C
Network Address: 200.129.41.
(^) Write it with the network octet in binary: 200.129.41. 0000 0000 break here (^) Borrowing 4 bits yields 14 usable subnets (^) How many usable hosts per subnet? (^) Same formula as subnets (2 m^ – 2 ) 4 host bits ( m = 8 – n = 8 – 4 = 4) (^24) – 2 = 16 – 2 = 14 usable hosts per subnet subnet bits host bits
Subnetting a Default Class C
Network Address: 200.129.41.
(^) Examples: 1 st usable subnet address: 200.129.41. 0001 ^ 0000 200.129.41. 16 1 st^ usable host on 1 st^ subnet: 200.129.41. 0001 ^ 0001 200.129.41. 17 2 nd^ usable host on 1 st^ subnet: 200.129.41. 0001 ^ 0010 200.129.41. 18 . . . Last usable host on 1 st subnet: 200.129.41. 0001 ^ 1110 200.129.41. 30 Broadcast Add. on 1 st subnet: 200.129.41. (^0001) ^ 1111 200.129.41. 31
The Subnet Mask: How the
Router Determines the Subnet
The subnet mask (in binary) has: all ones in the network and subnet portion of the address all zeros in the host potion of the address (^) The subnet mask for the previous example is: 255.255.255. 240 255.255.255. 1111 ^ 0000 (128 + 64 + 32 + 16 =240) ANDing this mask with any valid host address on the network will always yield the subnet address for that host.
The Subnet Mask: How the
Router Determines the Subnet
(^) Example (our subnet mask is 255.255.255. 240 ) IP host address: 200.129. 41. Last octet to binary: 200.129. 41. 0001 0111 AND subnet mask: 255.255.255. 1111 0000 200.129. 41.0001 0000 Subnet Address: 200.129. 41. 16 So the host address 200.129. 41.23 is on the 200.129.41.16 subnet.
Subnetting a Default Class B
Network Address: 132.178.0.
(^) Suppose we need 80 usable subnets, how many bits do we borrow? Remember, borrowing n bits give us: 2 n
- 2 subnets Try borrowing 6 bits ( n = 6) : 2 6
- 2 = 64 – 2 = 62 usable subnets (not enough) (^) Try borrowing 7 bits 2 7
- 2 = 128 – 2 = 126 usable subnets (enough)
Subnetting a Default Class B
Network Address: 132.178.0.
(^) Write it with the network octets in binary: 132.178.0000000 0. 00000000 break here (^) Borrowing 7 bits yields 126 usable subnets (^) How many usable hosts per subnet? (^) Same formula as subnets (2 n^ – 2 ) 9 host bits ( n = 9) (^29) – 2 = 512 – 2 = 510 usable hosts per subnet subnet bits host bits
Subnetting a Default Class B
Network Address: 132.178.0.
(^) Examples: Second usable 132.178. (^0000010) ^ 0. 00000000 subnet address: 132.178. 4. 0 Third usable 132.178. (^0000011) ^ 0. 00000000 subnet address: 132.178. 6. 0 . . . Ninety-first usable 132.178. (^1011011) ^ 0. 00000000 subnet address: 132.178. 182. 0 . . . Last usable 132.178. 1111110 ^
- 00000000 subnet address: 132.178. 252. 0
Subnetting a Default Class B
Network Address: 132.178.0.
(^) The subnet mask for this example is: 255.255. 254. 0 255.255. 1111111 ^
(^) ANDing this mask with any valid host address on this network will always yield the subnet address.