IP subnet

#defs_ccna

IP Subnet

IP Subnets are boundaries between logical networks in the IP space.

IPv4 Subnet masks can be written in dotted-decimal (e.g., 255.255.0.0), or in CIDR/slash notation (e.g., /16).
The first address in a subnet range is reserved for the Network Address, and the last address is reserved for the Broadcast Address
- Therefore, the number of host address is the size of the subnet range minus 2
It is the opposite of a Wildcard mask.

Shortcuts for Subnet Masks and Network Classes

**n = prefix multiple of 8 (/0, /8, /16, /24, /32)
Subnet Masks - Octet Divisions
1. 128 - /n+1
2. 192 - /n+2
3. 224 - /n+3
4. 240 - /n+4
5. 248 - /n+5
6. 252 - /n+6
7. 254 - /n+7
8. 255 - /n+8
Subnet Masks - Octet Increments
1. 128 - /n+1
2. 64 - /n+2
3. 32 - /n+3
4. 16 - /n+4
5. 8 - /n+5
6. 4 - /n+6
7. 2 - /n+7
8. 1 - /n+8
Network Class Divisions
- FORGET CLASS DIVISIONS; JUST REMEMBER HOW TO DO IT
1. Class A: 128 (0.0-127.255)
  1. Class A Private: (10.0-10.255) /8
2. Class B: 64 (128.0-191.255)
  1. Class B Private: (172.16.0-172.31.255) /12
3. Class C: 32 (192.0-223.255)
  1. Class C Private: (192.168.0-192.168.255) /16
4. Class D: 16 (224.0-239.255)
5. Class E: 16 (240.0-255.255)
Network classes
1. Valid Network Class C range is 192.0.0.0 to 223.255.255.0/24
2. Valid Network Class B range is 128.0.0.0 to 191.255.0.0/16
  1. Private range is 172.16.0.0 172.31.0.0 /12
3. Class A valid network addresses range from 1.0.0.0 to 126.0.0.0/8
  1. 0.0.0.0/8 is reserved by RFC to mean "this network"
4. Class D addresses range from 224.0.0.0 to 239.255.255.255

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OSI or TCP/IP Layer

CCNA Exam Topic

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