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Chapter 6. Subnetting Basicsl. Summary of the Three Classes of Networks. Subnetting. Benefits Reduce Network Traffic Routers breakup Broadcast Domains Optimal Performance Simplified Management Subnets Allow you to break large networks into smaller ones
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Chapter 6 Subnetting Basicsl
Subnetting • Benefits • Reduce Network Traffic • Routers breakup Broadcast Domains • Optimal Performance • Simplified Management • Subnets • Allow you to break large networks into smaller ones • Must take bits from the hostid part of the address • Always take from the left most hostid bits
Subnetting • Process of subdividing a single class of network into multiple, smaller networks FIGURE 11-2 IP address before and after subnets
Subnetting • Extended network prefix • The combination of an address’s network and subnet information • (netid,subnetid,hostid) • Subnet mask • Special 32-bit number • Only used within Internally • Used to determine (netid, subnetid – portion of an address
Subnetting IP Address and Subnet Mask are logically ANDed to determine the network/subnet portion of an IP address
Subnetting FIGURE 11-4 Subnetted network connected to the Internet
Subnetting Given: IP Address : 128.12.34.71 Subnet Mask: 255.255.240.0How many subnets? What is the Subnet Number? How many hosts? What is the Host Number? 11111111.11111111.11110000.00000000 14 32 4094 2.71
First Things First • Determine the number of networks needed • One for each subnetwork • One for each WAN segment • Determine the number of hosts required • One for each TCP/IP host • One for each Router interface • Create the following • A subnet mask for the entire network • A subnet id for each network segment • A range of host ids for each subnet segment
Subnetting Class C Addresses • Class C address = 8 host bits • Possible Subnet Mask Bits • 10000000 = 128 • 11000000 = 192 • 11100000 = 224 • 11110000 = 240 • 11111000 = 248 • 11111100 = 252 • 11111110 = 254 • Rules • Cannot have only 1 bit for subnetting or hostid • Subnets 128 & 254 are illegal
The Alternate Method 1. How many subnets does the subnet mask produce? • 2x x=number of bits for subnet 2. How many valid hosts per subnet? 2y • y=number of bits for host ids 3. What are the valid subnets? • 256 – subnet = first subnetwork (block) • add the block to subnetwork • stop when subnet mask is reached 4. What is the broadcast address of each subnet? • Next subnetwork – 1 5. What are the valid hosts in each subnet? • First Host = Subnetwork + 1 • Last Host = Broadcast - 1
Things to Know • Calculating subnet mask, host addresses, broadcast address • Understand the concept of VLSM • Four diagnostic steps