determine the home subnetwork for individual nodes. This process is referred to as logical ANDing. ANDing is a binary process by which the router calculates the subnetwork ID for an incoming packet. ANDing is similar to multiplication. This process is handled at the binary level. Therefore, it is necessary to view the IP address and mask in binary. The IP address and the subnetwork address are ANDed with the result being the subnetwork ID. The router then uses that information to forward the packet across the correct interface. Subnetting is a learned skill. It will take many hours performing practice exercises to gain a development of flexible and workable schemes. A variety of subnet calculators are available on the web. However, a network administrator must know how to manually calculate subnets in order to effectively design the network scheme and assure the validity of the results from a subnet calculator. The subnet calculator will not provide the initial scheme, only the final addressing. Also, no calculators, of any kind, are permitted during the certification exam. Web Links IP Addressing Subnetting Tutorial http://www.ralphb.net/IPSubnet

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Content Summary An understanding of the following key points should have been achieved:

• Routed or routable protocol characteristics
• The steps of data encapsulation in an internetwork as data is routed to one or more Layer 3 devices
• Connectionless and connection-oriented delivery
• The IP packet fields
• Routers operate at the network layer. Initially, the router receives a Layer 2 frame with a Layer 3 packet encapsulated within it. The router must strip off the Layer 2 frame and examine the Layer 3 packet. When the router is ready to transmit the packet, the router then must encapsulate the Layer 3 packet in a new Layer 2 frame.
• Routed protocols define the format and use of the fields within a packet. Packets generally are conveyed from end system to end system.
• LAN switching occurs at Layer 2 of the OSI reference model, and routing occurs at Layer 3.
• Routing protocols are used between routers to determine paths and maintain routing tables. Routed protocols are used to direct user traffic.
• Routing involves two basic activities: determining the best routing paths and transporting packets through an internetwork.
• Routing algorithms process routing updates and populate the routing table with the best routes.
• Routing tables contain the best routes to all known networks. These routes can be either static routes, which are entered manually, or dynamic routes, which are learned through routing protocols.
• Convergence describes the speed at which all routers agree on a change in the network.
• Interior routing protocols route data within autonomous systems, while exterior routing protocols route data between autonomous systems.
• Routers using distance-vector routing protocols periodically send routing updates consisting of all or part of its routing table. Routers using link-state routing protocols use link-state advertisements (LSAs) to send updates only when topological changes occur in the network, and send complete routing tables much less frequently.
• The uses for subnetting
• How to determine the appropriate subnet mask for a given situation
• How to subnet Class A, B, and C networks
• How to use a subnet mask to determine the subnet ID