Subnetting

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Subnetting is the process of logically dividing an IP network into small subnets.

• works at layer 3
• each subnet has a unique address
• subnetting scheme can be applied to represent a VLAN

Example

• The subnet design allocates separate subnets:
  • 10.0.1.0 and 10.0.2.0 for two VLANs configured on switch A
• and for the serial WAN links configured between Router A and Routers B and C (10.0.3.0 and 10.0.4.0).
• Routers B and C also have a subnet each for their local networks (10.0.5.0, 10.0.6.0)

• VLANs and subnets can be used for various design goals:
  • Organizations with multiple sites have WAN links as separate subnets
  • divide a network into logically distinct zones for security and administrative control
    • VLANs isolate a group of hosts, allowing incoming and outgoing traffic for the group to easily be filtered at the router
  • used to group hosts with similar performance to optimize network performance