VLSM TABLE & SUBNETTING (important) - Dleifnesor/NET-150 GitHub Wiki
The subnet mask uses 1s and 0s to indicate that the corresponding bits on the ip address are reserved for the network id and the rest for the host id range.
Network prefixes The address is followed by a number that represents the number of bits beginning fom the left that apply to a network a slash (/) is used to separate the address and the prefix length
Subnetting is the practice of dividing a network into smaller logical subnetworks (subnets). It improves routing efficiency, enhances security, and better utilizes IP address space.
IPv4 addresses are 32-bit numbers, typically written in dotted-decimal notation (e.g., 192.168.1.1).
| CIDR Notation | Subnet Mask | Number of Hosts | Number of Subnets |
|---|---|---|---|
| /8 | 255.0.0.0 | 16,777,214 | 1 |
| /16 | 255.255.0.0 | 65,534 | 256 |
| /24 | 255.255.255.0 | 254 | 65,536 |
| /30 | 255.255.255.252 | 2 | 1,073,741,824 |
Subnetting is the practice of dividing a network into smaller logical subnetworks (subnets). It improves routing efficiency, enhances security, and better utilizes IP address space.
IPv4 addresses are 32-bit numbers, typically written in dotted-decimal notation (e.g., 192.168.1.1).
| CIDR Notation | Subnet Mask | Number of Hosts | Number of Subnets |
|---|---|---|---|
| /8 | 255.0.0.0 | 16,777,214 | 1 |
| /16 | 255.255.0.0 | 65,534 | 256 |
| /24 | 255.255.255.0 | 254 | 65,536 |
| /30 | 255.255.255.252 | 2 | 1,073,741,824 |
- Identify Network and Host Portions: Use the subnet mask to distinguish.
- Determine Subnet Increment: Based on borrowed bits.
- Calculate Range of IP Addresses: Start from network address, increment by subnet size.
- IP Address:
192.168.10.0/24 - Subnet Mask:
255.255.255.0 - Subnets if divided further into /26:
| Subnet Address | First Host | Last Host | Broadcast Address |
|---|---|---|---|
| 192.168.10.0/26 | 192.168.10.1 | 192.168.10.62 | 192.168.10.63 |
| 192.168.10.64/26 | 192.168.10.65 | 192.168.10.126 | 192.168.10.127 |
IPv6 addresses are 128-bit numbers, written in hexadecimal colon-separated notation (e.g., 2001:0db8:85a3::8a2e:0370:7334).
| Prefix Length | Typical Use Case | Number of Subnets | Hosts per Subnet |
|---|---|---|---|
| /48 | Site (Large Organization) | 65,536 | ~1.2x10^24 |
| /56 | ISP allocation to a customer | 256 | ~4.7x10^21 |
| /64 | Standard single LAN segment | 1 | ~1.8x10^19 |
- Focus on the Network Portion: Often /48 or /64 boundaries.
- Borrow Bits to Subnet: Extend beyond default prefix (e.g., /64 to /68).
- Simplified Calculations: Each nibble (4 bits) aligns with a hexadecimal digit.
- IPv6 Address:
2001:db8:abcd::/48 - Dividing into /52 subnets:
| Subnet Address | Notes |
|---|---|
| 2001:db8:abcd:0::/52 | First subnet |
| 2001:db8:abcd:1000::/52 | Second subnet |
| 2001:db8:abcd:2000::/52 | Third subnet |
| Feature | IPv4 | IPv6 |
|---|---|---|
| Address Size | 32 bits | 128 bits |
| Subnetting Purpose | Maximize address efficiency | Facilitate efficient routing |
| Address Allocation | Scarce, careful assignment | Abundant, easier assignment |
| CIDR Flexibility | High | Moderate (commonly /64) |
- [RFC 4632 - Classless Inter-domain Routing (CIDR) for IPv4](https://datatracker.ietf.org/doc/html/rfc4632)
- [RFC 4291 - IPv6 Addressing Architecture](https://datatracker.ietf.org/doc/html/rfc4291)
- [Subnetting Practice Sites](https://www.subnettingpractice.com/)
Tip: Practice makes perfect. Regularly work through subnetting problems to build speed and accuracy.