CCNA1_M10_Routing_Fundamentals_Subnets (1130709)
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CCNA – Semester1Module 10Routing Fundamentals and SubnetsObjectives• Routed protocol• IP routing protocols• The mechanics of subnettingInternet Protocol - RoutedRouted protocols• A routed protocol allows the router to forwarddata between 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.• The network address is obtained by ANDing theaddress with the network mask.Routed protocolsConnection oriented network services••A connection is established between the sender and therecipient before any data is transferred.All packets travel sequentially across the same circuit, ormore commonly, across the same virtual circuit.Connectionless network services••Each packet is treated separatelyWhen the packets pass from source to destination, they can:– Switch to different paths.– Arrive out of order.IP as a Routed Protocol• IP is a connectionless,unreliable, best-effortdelivery protocol.• IP does not verify thatthe data reached itsdestination.
Thisfunction is handled bythe upper layerprotocols.Packet PropagationProcess in RouterIP header format20bytesIP header format: Version••••44 bits.bits.IndicatesIndicates thethe versionversion ofofIPIP currentlycurrently used.used.––––IPv4IPv4::01000100IPv6IPv6::01100110IP header format: Header length••••44 bits.bits.IPIP headerheader lengthlength :: IndicatesIndicates thethedatagramdatagram headerheader lengthlength inin 3232 bitbitwordswords (4(4 bits),bits), andand thusthus pointspoints totothethe beginningbeginning ofof thethe data.data.IP header format: Service type••••88 bits.bits.SpecifiesSpecifies thethe levellevel ofof importanceimportancethatthat hashas beenbeen requestedrequested forfor thisthisdatagramdatagram byby anan upper-layerupper-layerprotocol.protocol.••••••Precedence.Precedence.Reliability.Reliability.Speed.Speed.IP header format: Total length••••1616 bits.bits.SpecifiesSpecifies thethe lengthlength ininbytesbytes ofofthethe entireentire IPIP packet,packet, includingincludingdatadata andand header.header.IP header format: Identification••••1616 bits.bits.ContainsContains anan integerinteger thatthat identifiesidentifiesthethe currentcurrent datagram.datagram.•• AssignedAssigned byby thethe sendersender toto aidaid ininassemblingassembling thethe fragmentsfragments ofof aadatagram.datagram.IP header format: Flags••••33 bits.bits.TheThe secondsecond bitbit specifyingspecifying whetherwhether thethepacketpacket cancan bebe fragmentedfragmented ..•• TheThe lastlast bitbit specifyingspecifying whetherwhether thethepacketpacket isis thethe lastlast fragmentfragment inin aa seriesseries ofoffragmentedfragmented packets.packets.IP header format: Fragment offset•• 1313 bits.bits.•• UsedUsedwithwithfragmentedfragmenteddatagrams,datagrams,totoaidaidininreassemblyreassemblyofofthethefullfulldatagram.datagram.•• IsIsthethenumbernumberofof64-bit64-bitpiecespieces(header(headerbytesbytesarenotcounted)thatarecontainedinare not counted) that are contained inearlierearlierfragments.fragments.•• InInthethefirstfirst(or(oronly)only)fragment,fragment,thisthisvaluevalueisisalwaysalwayszero.zero.IP header format: Time to Live•• 88bits,bits,specifiesspecifiesthethetimetimeandanddistancedistancethisthisdatagramdatagramisisallowedallowedtototravel.travel.•• EachEachrouterrouterroutingroutingthisthisdatagramdatagramsubtractssubtractsfromfromthisthisfieldfielditsitsprocessingprocessingtimetimeforforthisthisdatagram,whichgraduallydecreasesdatagram, which gradually decreasesit.it.•• ItIthelpshelpspreventpreventpacketspacketsfromfromloopingloopingendlessly.endlessly.IP header format: Protocol•• IndicatesIndicates whichwhich upperupper protocolprotocolreceivesreceives incomingincoming packetspackets afterafter IPIPprocessingprocessing hashas beenbeen completedcompleted••••••0606::TCPTCP1717::UDPUDP01:ICMP01: ICMPIP header format: Header checksum••••1616 bits.bits.AA checksumchecksum onon thethe headerheader only,only,helpshelps ensureensure IPIP headerheader integrity.integrity.IP header format: Addresses••••••3232 bitsbits each.each.SourceSource IPIP AddressAddressDestinationDestination IPIP AddressAddressIP header format: Options••••VariableVariable length.length.AllowsAllows IPIP toto supportsupport variousvariousoptions,options, suchsuch asas security,security, route,route,errorerror reportreport ......IP header format: Padding•• TheThe headerheader paddingpadding isis usedused totoensureensure thatthat thethe internetinternet headerheader endsendsonon aa 3232 bitbit boundary.boundary.IP header format: Padding•• ContainsContainsupper-protocolupper-protocolinformation,information,variablelengthupto64Kb.variable length up to 64 Kb.•www.ietf.org and RFC-760.IP Routing ProtocolRouting Overview•••Routing is an OSI Layer 3function.Routing is the process offinding the most efficient pathfrom one device to another.Two key functions of router:– maintain routing tables– use the routing table to forwardpacketsLayer 2 Switching and Layer 3 RoutingRouting vs.
SwitchingRouting Protocol•Routing protocols allowrouters to choose the bestpath for data from source todestination. A routingprotocol functions includesthe following:– Provides processes forsharing route information– Allows routers tocommunicate with otherrouters to update andmaintain the routing tables•Eg:RIP, IGRP, OSPF, EIGRP,BGPRouted vs. Routing protocolols edcotrot rou etspng how packituRo rmine routestede tocolproPath Determination• Path determination enables a router to compare thedestination address to the available routes in itsrouting table, and to select the best path.• The router uses path determination to decide whichport an incoming packet should be sent out of totravel on to its destination.Routing Tables• Routing tables contain the information of a route toforward data packets across connected networks :––––Protocol typeDestination/next-hop associationsRoute metric and routing protocol reliabilityOutbound interfacesRouting Algorithms• Routing protocols often have one or more of thefollowing design goals:–––––OptimizationSimplicity and low overheadRobustness and stabilityFlexibilityRapid convergenceRouting Metrics•Metrics can be based on a single characteristic of a path, orcan be calculated based on several characteristics.
Thefollowing are the metrics that are most commonly used byrouting protocols:–––––Bandwidth: The data capacity of a linkDelay: The length of time required to move a packet along each linkLoad: The amount of activity on a network resourceReliability: Usually a reference to the error rateHop count: The number of routers that a packet must travel throughbefore reaching its destination– Ticks: delay on a data link using IBM PC clock ticks. One tick isapproximately 1/18 second.– Cost: An arbitrary value, usually based on bandwidth, monetaryexpense, or other measurement, that is assigned by a networkadministrator.IGP and EGP• An autonomous system is a network or set of networksunder common administrative control.• Two families of routing protocols are:– Interior Gateway Protocols(IGPs): exchange routes within an autonomoussystem.
Eg: RIP, IGRP, OSPF, IS-IS…– Exterior Gateway Protocols(EGPs): exchange routes betweenautonomous systems. Eg: BGPLink state and distance vector• Distance-Vector Protocols (RIP, IGRP, EIGRP):––––View network topology from neighbor’s perspective.Add distance vectors from router to router.Frequent, periodic updates.Pass copy of routing tables to neighbor routers.• Link State Protocols (OSPF, IS - IS):––––Gets common view of entire network topology.Calculates the shortest path to other routers.Event-triggered updates, respond quickly to network changes .Passes link state advertisement, known as link-state refreshes,to other routers.Distance vector routingLink state routingThe Mechanics of SubnettingWhy we need to divide network?• Network administrators sometimes need to dividenetworks, especially large ones, into smaller networks:– Reduce the size of a broadcast domain.– Support basic network security.– Implement the hierarchical managements.• So we need more network addresses for your network.But I want the outside networks see our network as asingle network.Subnetting••Subnetworks are smaller divisions of network.To create a subnet address, a network administrator borrowsbits from the original host portion and designates them as thesubnet field.How ?By using subnetmaskSubnet mask• “Extended Network Prefix”.• Determines which part of an IP address is thenetwork field and which part is the host field.• 32 bits long.• Divided into four octets.• Network and Subnet portions all 1’s.• Host portions all 0’s.Default subnet mask: Example•••••192.168.2.100 / 255.255.255.0.11000000.10101000.00000010.01100100.11111111.11111111.11111111.00000000.11000000.10101000.00000010.01100100.Class C network:– 24 bits for network portion.– 0 bits for subnet portion.– 8 bits for host portion.• Subnet address: 192.168.2.0Subnet mask: Example•••••172.16.65.100 / 255.255.240.0.10101100.00010000.01000001.01100100.11111111.11111111.11110000.00000000.10101100.00010000.01000001.01100100.Class B network:– 16 bits for network portion.– 4 bits for subnet portion.– 12 bits for host portion.• Subnet address: 172.16.64.0.How many bits can I borrow?• All of subnet bits are:– 0 : reserved for network address.– 1 : reserved for broadcast address.• The minimum bits you can borrow is: 2 bits.• The maximum bits you can borrow is: Number of host bits -2 bits• Slash mask is the sum total of all bits assigned tothe subnet field plus the fixed network bits.
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