*What the router does 1Ethernet frame received from PC1 through port Fa0/0Destination MAC address is routers address

*What the router does 2Strip off frame header and trailer (decapsulate)Read destination IP address 192.168.4.9

*What the router does 3Logical AND with IP address 192.168.4.9 and subnet mask 255.255.255.0 (/24) gives destination network address 192.168.4.0

*What the router does 4Look in routing table for network address 192.168.4.0Route found via 192.168.3.2 through S0/0

*What the router does 5S0/0 connects to a WAN link using PPPEncapsulate packet in PPP frameSend frame out through S0/0

*No route foundIf the destination network is not in the routing table:Use a default route if one existsOtherwise drop the packet and send an ICMP (Internet Control Message Protocol ) destination unreachable message to the source host.

*Show ip routeList of codesList of routes

*Routing tableC 192.168.1.0/24 is directly connected, FastEthernet0/0C 192.168.2.0/24 is directly connected, Serial0/0

S 192.168.3.0/24 [1/0] via 192.168.2.2R 192.168.4.0/24 [120/1] via 192.168.2.2, 00:00:20, Serial0/0Network and maskExit port

*Routing tableC 192.168.1.0/24 is directly connected, FastEthernet0/0C 192.168.2.0/24 is directly connected, Serial0/0

S 192.168.3.0/24 [1/0] via 192.168.2.2

R 192.168.4.0/24 [120/1] via 192.168.2.2, 00:00:20, Serial0/0Static routeNetwork and maskAdministrative distance and metricAddress of next hop router

*Routing tableC 192.168.1.0/24 is directly connected, FastEthernet0/0C 192.168.2.0/24 is directly connected, Serial0/0S 192.168.3.0/24 [1/0] via 192.168.2.2R 192.168.4.0/24 [120/1] via 192.168.2.2, 00:00:20, Serial0/0Dynamic route, RIPNetwork and maskAdministrative distance and metricAddress of next hop routerTime since last updateExit port

Static routes Dynamic routesEntered by administratorTime consuming, different for each routerMust be updated if routes changeLittle processingNo bandwidth usedLearned from other routersStart the protocol then it runs by itselfAutomatically updates when routes changeMore processingUses bandwidth

Routing protocolsInterior, used within an organisations networksExterior, used between different organisations networksBGPOSPFIS-ISDistance vectorLink stateRIP(IGRP) EIGRP

Routing Table Principles1. Every router makes its decision alone, based on the information it has in its own routing table. 2. The fact that one router has certain information in its routing table does not mean that other routers have the same information. 3. Routing information about a path from one network to another does not provide routing information about the reverse, or return, path.

MetricsA routing protocol may learn of several possible routes to a destination.It uses metrics to pick the best route.RIP uses hop count as its only metric.OSPF uses cost based on bandwidth.EIGRP uses bandwidth and delay and can use load and reliability as well.

MetricsRIP uses hop count. It picks this route as the best.OSPF uses cost based on bandwidth. It picks this route as the best.

Administrative distanceIs the measure used by Cisco routers to select the best path when there are two or more different routes to the same destination from two different routing protocolsThere may be more than one routing protocol running. There may also be static routes.Static routes have administrative distance 1 or 0 by default.RIP routes have administrative distance 120OSPF routes have administrative distance 110The route with the lowest administrative distance goes in the routing table

CDP show commandsShow cdp neighbors command-Displays the following information:Neighbor device IDLocal interfaceHoldtime value, in secondsNeighbor device capability codeNeighbor hardware platformNeighbor remote port IDShow cdp neighbors detail command -Useful in determining if an IP address configuration error

Purpose of a static routeA manually configured route used when routing from a network to a stub networkStub networknetworksStatic routeDefault route

Topology & Routing table

General Role of the RouterConnections of a Router for WAN -A router has a DB-60 port that can support 5 different cabling standardsConnections of a Router for Ethernet-2 types of connectors can be used: Straight through and Cross-over Straight through used to connect:-Switch-to-Router, Switch-to-PC, Router-to-Server, Hub-to-PC, Hub-to-ServerCross-over used to connect: -Switch-to-Switch, PC-to-PC, Switch-to-Hub, Hub-to-Hub, Router-to-Router

Examining Router Interfaces-Show IP route command used to view routing table-Show Interfaces command used to show status of an interface-Show IP Interface brief command used to show a portion of the interface information-Show running-config command used to show configuration file in RAM

IP route commandTo configure a static route use the following command: ip routeExample:-Router(config)# ip route network-address subnet-mask {ip-address | exit-interface }

Configuring routes to 2 or more remote networksUse the following commands for R1-R1(config)#ip route 192.168.1.0 255.255.255.0 172.16.2.2-R1(config)#ip route 192.168.2.0 255.255.255.0 172.16.2.2

Ethernet interfaces and ARP If a static route is configured on an Ethernet link-If the packet is sent to the next-hop router then the destination MAC address will be the address of the next hops Ethernet interfaceThis is found by the router consulting the ARP table. If an entry isnt found then an ARP request will be sent out

Static Routes with Exit InterfacesIP route commandTo configure a static route use the following command: ip routeExample:-Router(config)# ip route network-address subnet-mask {ip-address | exit-interface }

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