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Subnetting is a fundamental skill for network administrators and cybersecurity professionals. Understanding IPv4 and IPv6 subnet masks helps in efficient IP address allocation, network segmentation, and security enforcement. Below is a detailed cheat sheet along with practical commands and examples.
IPv4 Subnet Mask Cheat Sheet
| CIDR | Subnet Mask | Number of Hosts |
||-|–|
| /32 | 255.255.255.255 | 1 |
| /24 | 255.255.255.0 | 254 |
| /16 | 255.255.0.0 | 65,534 |
| /8 | 255.0.0.0 | 16,777,214 |
IPv6 Subnet Mask Cheat Sheet
| Prefix Length | Example IPv6 Subnet | Hosts Available |
|||–|
| /64 | 2001:db8::/64 | 18,446,744,073,709,551,616 |
| /56 | 2001:db8::/56 | 4,722,366,482,869,645,000 |
| /48 | 2001:db8::/48 | 1,208,925,819,614,629,000 |
You Should Know:
1. Calculating Subnets in Linux
Use `ipcalc` to determine subnet ranges:
ipcalc 192.168.1.0/24
Output:
Address: 192.168.1.0 Netmask: 255.255.255.0 Network: 192.168.1.0/24 HostMin: 192.168.1.1 HostMax: 192.168.1.254
2. Configuring IPv6 on Linux
Assign an IPv6 address:
ip -6 addr add 2001:db8::1/64 dev eth0
Verify:
ip -6 addr show eth0
3. Windows Subnet Commands
Check subnet mask in Windows:
ipconfig /all
Add a static route:
route add 192.168.2.0 mask 255.255.255.0 192.168.1.1
4. Subnetting for Security
Restrict SSH access to a subnet:
sudo ufw allow from 192.168.1.0/24 to any port 22
5. IPv6 Firewall Rule (Linux)
Allow ICMPv6 (essential for IPv6):
sudo ip6tables -A INPUT -p icmpv6 -j ACCEPT
6. Network Scanning with Nmap
Scan a subnet for live hosts:
nmap -sn 192.168.1.0/24
7. Convert CIDR to Subnet Mask (Python)
import ipaddress
net = ipaddress.IPv4Network("192.168.1.0/24")
print("Subnet Mask:", net.netmask)
What Undercode Say
Subnetting is crucial for optimizing network performance and security. By mastering IPv4 and IPv6 subnet masks, you can:
– Reduce broadcast traffic
– Implement Zero Trust segmentation
– Detect unauthorized IP ranges
– Prevent lateral movement in cyber attacks
Advanced Commands:
- List all IPv6 neighbors:
ip -6 neighbor show
- Check IPv6 routing table:
ip -6 route show
- Test IPv6 connectivity:
ping6 2001:db8::1
Expected Output:
Address: 192.168.1.0 Netmask: 255.255.255.0 Network: 192.168.1.0/24 HostMin: 192.168.1.1 HostMax: 192.168.1.254
References:
Reported By: Https: – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
