📖 What is Subnet Mask?
A 32-bit number that masks an IP address, dividing the IP address into network address and host address portions.
🥋
Sensei Says:
"The / notation (CIDR) is essential. If you see /27, you should instantly know the mask is 255.255.255.224 and provides 30 usable host addresses per subnet."
📚 Certification: Certified Network Associate (200-301)
🔑 What are the Key Concepts of Subnet Mask?
- ▸ Contiguous 1s followed by contiguous 0s in binary.
- ▸ Determines network and host boundaries.
- ▸ CIDR notation (e.g., /24) as shorthand.
🎯 How does Subnet Mask appear on the 200-301 Exam?
Determine the correct subnet mask to satisfy a specific requirement for number of hosts.
Identify if two IP addresses are on the same subnet based on their subnet mask.
❓ Frequently Asked Questions
Can a subnet mask have alternating 1s and 0s?
No, a valid subnet mask must consist of consecutive 1s followed by consecutive 0s.
What is a /30 subnet used for?
It provides exactly 2 usable host addresses, making it perfect for point-to-point serial links or router interconnects.
Related Terms from Certified Network Associate
Root Bridge
VLAN (Virtual Local Area Network)
MAC Address Table
Link Aggregation Control Protocol (LACP)
Directly Connected Static Route
OSPF Router ID (RID)