Subnet Mask

• Subnet mask is a 32 bits long address used to distinguish between network address and host address in IP address.
• Subnet mask is always used with IP address. Subnet mask has only one purpose, to identify which part of an IP address is network address and which part is host address.

Default Subnet Masks
Address Class	Subnet Mask length	# of networks	# of hosts	Subnet Mask
Class A	8	126	16,777,214	255.0.0.0
Class B	16	16,382	65,534	255.255.0.0
Class C	24	2,097,150	254	255.255.255.0

What is subnet

• Subnetting is the process of dividing a network and it's IP address into segments, each of which is called a subnetwork or subnet.

Advantages

• Reduced network traffic.
• Optimized network performance.
• Simplified management.
• Facilitated spanning of large geographical distances.

Disadvantages

• Costs – Reliable network equipment such as routers, switches, hubs, bridges, etc are very pricey.
• Support – Sub-netting and network management in general requires an experienced network administrator.