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Objectives Routed protocol IP routing protocols The mechanics of subnetting
Routable and RoutedProtocolsA routed protocol allows the router to forwarddata between nodes on different networks.In order for a protocol to be routable, it mustprovide the ability to assign a network numberand a host number to each individual device.These protocols also require a network maskin order to differentiate the two numbers.The reason that a network mask is used is toallow groups of sequential IP addresses to betreated as a single unit.
IP as a Routed ProtocolIP is aconnectionless,unreliable, best-effortdelivery protocol.As information flowsdown the layers of theOSI model; the datais processed at eachlayer.IP accepts whateverdata is passed downto it from the upperlayers.
Packet Propagation andSwitching Within a Router
Packet Propagation andSwitching Within a RouterAs a frame is received at a router interface.The MAC address is checked to see if theframe is directly addressed to the routerinterface, or a broadcast.The frame header and trailer are removedand the packet is passed up to Layer 3.The destination IP address is compared tothe routing table to find a match.The packet is switched to the outgoinginterface and given the proper frame header.The frame is then transmitted.
Internet Protocol (IP): ConnectionlessThe Internet is a gigantic, connectionless networkin which all packet deliveries are handled by IP.TCP adds Layer 4, connection-oriented reliabilityservices to IP.
Telephone Calls: Connection-orientedA connection is established between thesender and the recipient before any data istransferred.
Anatomy of an IP PacketWhile the IP source and destinationaddresses are important, the other headerfields have made IP very flexible.The header fields are the information thatis provided to the upper layer protocolsdefining the data in the packet.
Routing OverviewA router is a network layer device that uses one ormore routing metrics to determine the optimal path.Routing metrics are values used in determining theadvantage of one route over another.Routing protocols use various combinations ofmetrics for determining the best path for data.
Routing Versus SwitchingThis distinction is routing and switchinguse different information in the process ofmoving data from source to destination.
Routed Versus RoutingA routed protocol: Includes any network protocol suite that provides enough information in its network layer address to allow a router to forward it to the next device and ultimately to its destination. Defines the format and use of the fields within a packet.A routing protocol: Provides processes for sharing route information. Allows routers to communicate with other routers to update and maintain the routing tables.
Path DeterminationPath determination enables a router to comparethe destination address to the available routes inits routing table, and to select the best path.
Routing TablesRouters keep track of the following: Protocol type Destination/next-hop associations Routing metric Outbound interfaces
Routing Algorithms andMetricsRouting protocols have one or more of thefollowing design goals: Optimization Simplicity and low overhead Robustness and stability Flexibility Rapid convergence
IGP and EGPIGPs route data within an autonomous system. RIP, RIPv2, IGRP, EIGRP, OSPF, IS-ISEGPs route data between autonomous systems Border Gateway Protocol (BGP)
Link State and DistanceVector Examples of distance-vector protocols: Routing Information Protocol (RIP) Interior Gateway Routing Protocol (IGRP) Enhanced IGRP (EIGRP) Examples of link-state protocols: Open Shortest Path First (OSPF) Intermediate System-to-Intermediate System (IS-IS)
Introduction to SubnettingHost bits mustare reassigned(or “borrowed”) 3 bits borrowed allows 23-2 or 6 subnetsas networkbits.The startingpoint is always 5 bits borrowed allows 25-2 or 30 subnetsthe leftmosthost bit. 12 bits borrowed allows 212-2 or 4094 subnets
Reasons for SubnettingProvides addressing flexibility for thenetwork administrator. Each LAN must have its own network or subnetwork address.Provides broadcast containment and low-level security on the LAN.Provides some security since access toother subnets is only available through theservices of a router.
Establishing the Subnet Mask AddressDetermines which part of an IP address is the networkfield and which part is the host field.Follow these steps to determine the subnet mask: 1. Express the subnetwork IP address in binary form. 2. Replace the network and subnet portion of the address with all 1s. 3. Replace the host portion of the address with all 0s. 4. Convert the binary expression back to dotted-decimal notation.
Establishing the Subnet MaskAddressTo determine the number of bits to be used, thenetwork designer needs to calculate how manyhosts the largest subnetwork requires and thenumber of subnetworks needed.The “slash format” is a shorter way ofrepresenting the subnet mask: /25 represents the 25 one bits in the subnet mask 255.255.255.128
Subnetting Class A and BNetworksThe available bits for assignment to thesubnet field in a Class A address is 22 bitswhile a Class B address has 14 bits.
Calculating the Subnetwork With ANDing ANDing is a binary process by which the router calculates the subnetwork ID for an incoming packet. 1 AND 1 = 1; 1 AND 0 = 0; 0 AND 0 = 0 The router then uses that information to forward the packet across the correct interface. 11000000.10101000.00001010.0Packet Address 192.168.10.65 00001 10 11111111.11111111.11111111.1Subnet Mask 255.255.255.224 00000 11 11000000.10101000.00001010.0Subnetwork Address 192.168.10.64 00000 10