CCNA-Day3

Distance VectorLink StateHybridDistance Vector vs. Link StateRoute tableTopologyIncremental UpdatePeriodic UpdateRouting by rumorABCDXE

Distance Vector vs. Link StateDistance VectorUpdates frequentlyEach router is "aware" only of its immediate neighborsSlow convergenceProne to routing loopsEasy to configureLink StateUpdates are event triggeredEach router is "aware" of all other routers in the "area"Fast convergenceLess subject to routing loopsMore difficult to configure

Comparison ContinuedDistance VectorFewer router resources requiredUpdates require more bandwidthDoes not "understand" the topology of the networkLink StateMore router resource intensiveUpdates require less bandwidthHas detailed knowledge of distant networks and routers

Link State Routing

Link StateExampleOSPFIS-IS

OSPF is used for corporate networksIS-IS is used for ISPs

Open Shortest Path First (OSPF)OSPF is an open standards routing protocol This works by using the Dijkstra algorithmOSPF provides the following features:Minimizes routing update trafficAllows scalability (e.g. RIP is limited to 15 hops)Has unlimited hop countSupports VLSM/CIDRAllows multi-vendor deployment (open standard)

Link StateThere are two types of PacketsHelloLSAs

OSPF HelloWhen router A starts it send Hello packet uses 224.0.0.5Hello packets are received by all neighborsB will write As name in its neighbor tableC also process the same way

ABC

"Hello" PacketsSmall frequently issued packetsDiscover neighbours and negotiate "adjacencies"Verify continued availability of adjacent neighboursHello packets and Link State Advertisements (LSAs) build and maintain the topological databaseHello packets are addressed to 224.0.0.5.

Link State Advertisement(LSA)An OSPF data packet containing link state and routing information that is shared among OSPF routers

LSAs are shared only with routers with whom it has formed adjacencies

LSA packets are used to update and maintain the topology database.

Link StateThere are three type of tablesNeighborTopologyRouting

TablesNeighborContain information about the neighborsNeighbor is a router which shares a link on same networkAnother relationship is adjacencyNot necessarily all neighborsLSA updates are only when adjacency is established

TablesTopologyContain information about all network and path to reach any networkAll LSAs are entered in to topology tableWhen topology changes LSAs are generated and send new LSAsOn topology table an algorithm is run to create a shortest path, this algorithm is known as SPF or dijkstra algorithm

TablesRouting TableAlso knows as forwarding databaseGenerated when an algorithm is run on the topology databaseRouting table for each router is unique

OSPF TermsLinkRouter IDNeighboursAdjacencyOSPF AreaBackbone areaInternal routersArea Border Router (ABR)Autonomous System Boundary Router (ASBR)

LinkA network or router interface assigned to a given networkLink (interface) will have "state" information associated with itStatus (up or down)IP AddressNetwork type (e.g. Fast Ethernet)BandwidthAddresses of other routers attached to this interface

OSPF Term: LinkA link is a network or router interface assigned to any given network This link, or interface, will have state information associated with it (up or down) as well as one or more IP addresses

OSPF Term: Link StateStatus of a link between two routersInformation is shared between directly connected routers. This information propagates throughout the network unchanged and is also used to create a shortest path first (SPF) tree.

Router IDThe Router ID (RID) is an IP address used to identify the router

Cisco chooses the Router ID by using the highest IP address of all configured loopback interfaces

If no loopback interfaces are configured with addresses, OSPF will choose the highest IP address of all active physical interfaces.

You can manually assign the router ID.

The RID interface MUST always be up, therefore loopbacks are preferred

NeighboursNeighbours are two or more routers that have an interface on a common networkE.g. two routers connected on a serial linkE.g. several routers connected on a common Ethernet or Frame relay networkCommunication takes place between / among neighboursneighbours form "adjacencies"

AdjacencyA relationship between two routers that permits the direct exchange of route updatesNot all neighbours will form adjacenciesThis is done for reasons of efficiency more later

OSPF DesignEach router connects to the backbone called area 0, or the backbone area.

Routers that connect other areas to the backbone within an AS are called Area Border Routers (ABRs). One interface must be in area 0.

OSPF runs inside an autonomous system, but can also connect multiple autonomous systems together. The router that connects these ASes together is called an Autonomous System Boundary Router (ASBR).

OSPF AreasAn OSPF area is a grouping of contiguous networks and routersShare a common area IDA router can be a member of more than one area (area border router)All routers in the same area have the same topology databaseWhen multiple areas exist, there must always be an area 0 (the backbone) to which other areas connect

Why areas?Decreases routing overheadCompare to multiple smaller broadcast domains instead of one large one

Speeds convergence

Confines network instability (e.g. route "flapping") to single area of the network

Adds considerably to the complexity of setting up OSPFCCNA certification deals only with single-area OSPF

Area Terminology

LSAs in AreaLSAs communicate with adjacent routers in the same OSPF area

Subsequently, a change in a link state is "flooded" to all area routers via LSAs

In larger networks, multiple areas may be createdLSAs are sent only to adjacent routers in the same area"Area border routers" connect areas, passing summarized route information between

Path CalculationChanges to the topological database of a router trigger a recalculation to re-establish the best route(s) to known networksUses the SPF (shortest path first) algorithm developed by a computer scientist named DijkstraThis is done by each individual router using its detailed "knowledge" of the whole networkLeads to rapid and accurate convergenceBased on detailed knowledge of every link in the area and the OSPF "cost" of eachbuilds an OSPF tree with itself at the route

Terminology: CostVarious criteria can be selected by the administrator to determine the metricUsually, OSPF cost=108/bandwidthDo not forget to configure the bandwidth` command on serial links to ensure correct default OSPF cost

Pros and ConsNote that OSPF is a more sophisticated routing protocolConverges rapidly and accuratelyCan use a metric calculation that effectively selects the "best" route(s) primarily based on bandwidth, although an OSPF cost can be administratively assignedUse of OSPF requiresMore powerful routing hardwareMore detailed knowledge by the administrator, especially when large multi-area networks are used

Types of NeighborsOSPF can be defined for three type of neighborsBroadcast Multi Access (BMA) ex- EthernetPoint to PointNon-Broadcast Multi Access (NBMA)

OSPF Network Types

AdjacenciesPoint to Point all routers form adjacenciesBMA & NBMA one router is elected as DRDR establish adjacency with every neighbor routerLSA updates are exchanged only to DRDR is the router which has highest priorityAll CISCO routers has priority 1If priority is same then router id is seenThe RID is highest IP address of all interfaces

Point-to-Point Links Usually a serial interface running either PPP or HDLC No DR or BDR election required OSPF autodetects this interface type OSPF packets are sent using multicast 224.0.0.5All routers form adjacencies

Multi-access Broadcast Network Generally LAN technologies like Ethernet and Token Ring DR and BDR selection required All neighbor routers form full adjacencies with the DR and BDR only Packets to the DR use 224.0.0.6 Packets from DR to all other routers use 224.0.0.5

Electing the DR and BDR Hello packets are exchanged via IP multicast. The router with the highest priority is selected as the DR.If Priority is same then Router ID is seen Use the OSPF router ID as the tie breaker.

Terminology: DRs and BDRsThe designated router (DR) is responsible for generating LSAs on behalf of all routers connected to the same segment

DR ResponsibilityWhen a router sees a new or changed link-state, it sends an LSA to its DR using a particular multicast address

The DR then forwards the LSA to all the other routers with whom it is adjacentMinimizes the number of formal adjacencies that must be formed and therefore the amount of LSU (link state update) packet traffic in a multi-router network

OSPF SummaryAD -100Hop count is unlimitedMetric = Cost 108/BWClassless, VLSMLoad balance up to SIX routersRequire more processing power

Basic OSPF ConfigurationRouter(config)# router ospf 1The number 1 in this example is a process-id # that begins an OSPF process in the routerMore than one process can be launched in a router, but this is rarely necessaryUsually the same process-id is used throughout the entire network, but this is not requiredThe process-id # can actually be any value from 1 to "very large integerThe process-id # cannot be ZEROThis is NOT the same as the AS# used in IGRP and EIGRP

Configuring OSPF Areas After identifying the OSPF process, you need to identify the interfaces that you want to activate OSPF communications Lab_A#config tLab_A(config)#router ospf 1Lab_A(config-router)#network 10.0.0.0 0.255.255.255area ? OSPF area ID as a decimal valueA.B.C.D OSPF area ID in IP address formatLab_A(config-router)#network 10.0.0.0 0.255.255.255area 0Every OSPF network must have an area 0 (the backbone area) to which other areas connectSo in a multiple area network, there must be an area 0The wildcard mask represents the set of hosts supported by the network and is really just the inverse of the subnet mask.

OSPF ConfigurationOSPF Process ID number is irrelevant. It can be the same on every router on the network The arguments of the network command are the network number (10.0.0.0) and the wildcard mask (0.255.255.255) Wildcards - A 0 octet in the wildcard mask indicates that the corresponding octet in the network must match exactly A 255 indicates that you dont care what the corresponding octet is in the network number A network and wildcard mask combination of 1.1.1.1 0.0.0.0 would match 1.1.1.1 only, and nothing else.The network and wildcard mask combination of 1.1.0.0 0.0.255.255 would match anything in the range 1.1.0.01.1.255.255

OSPF Configuration -110.0.0.120.0.0.120.0.0.230.0.0.130.0.0.240.0.0.110.0.0.240.0.0.2

OSPF Configuration -1R1#config tEnter configuration commands, one per line. End with CNTL/Z.R1(config)#router ospf 1R1(config-router)#network 10.0.0.0 0.255.255.255 area 0R1(config-router)#network 20.0.0.0 0.255.255.255 area 0 R1(config-router)#^Z

OSPF Configuration -2200.0.0.16/28200.0.0.8/30200.0.0.12/30200.0.0.32/27

OSPF Configuration -2200.0.0.17200.0.0.9200.0.0.10200.0.0.13200.0.0.14200.0.0.33200.0.0.18200.0.0.34255.255.255.240 255.255.255.252 255.255.255.252 255.255.255.224

OSPF Configuration -2200.0.0.17200.0.0.9200.0.0.10200.0.0.13200.0.0.14200.0.0.33200.0.0.18200.0.0.34255.255.255.240 255.255.255.252 255.255.255.252 255.255.255.224 R1#config tEnter configuration commands, one per line. End with CNTL/Z.R1(config)#router ospf 1R1(config-router)#network 200.0.0.16 0.0.0.15 area 0R1(config-router)#network 200.0.0. 8 0.0.0.3 area 0 R1(config-router)#^ZR3#config tEnter configuration commands, one per line. End with CNTL/Z.R3(config)#router ospf 1R3(config-router)#network 200.0.0. 32 0.0.0.31 area 0R3(config-router)#network 200.0.0. 12 0.0.0.3 area 0 R3(config-router)#^Z

OSPF and Loopback InterfacesConfiguring loopback interfaces when using the OSPF routing protocol is importantCisco suggests using them whenever you configure OSPF on a router Loopback interfaces are logical interfaces, which are virtual, software-only interfaces; they are not real router interfaces Using loopback interfaces with your OSPF configuration ensures that an interface is always active for OSPF processes.The highest IP address on a router will become that routers RID The RID is used to advertise the routes as well as elect the DR and BDR. If you configure serial interface of your router with highest IP Address this Address becomes RID of t is the RID of the router because e routerIf this interface goes down, then a re-election must occurIt can have an big impact when the above link is flapping

Configuring Loopback Interfaces R1#config tEnter configuration commands, one per line. End with CNTL/Z.R1(config)#int loopback 0R1(config-if)#ip address 172.16.10.1 255.255.255.255R1(config-if)#no shutR1(config-if)#^ZR1#

Verifying OSPF Operationshow ip protocols Router#Verifies the configured IP routing protocol processes, parameters and statisticsshow ip route ospfRouter#Displays all OSPF routes learned by the routershow ip ospf interface Router#Displays the OSPF router ID, area ID and adjacency information

Verifying OSPF Operation (Cont.)show ip ospf Router#Displays the OSPF router ID, timers, and statistics

show ip ospf neighbor [detail]Router#Displays information about the OSPF neighbors, including Designated Router (DR) and Backup Designated Router (BDR) information on broadcast networks

The show ip route ospf CommandRouterA# show ip route ospf Codes:C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP, D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area, E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP, i - IS-IS, L1 - IS-ISlevel-1, L2 - IS-IS level-2, * - candidate default

Gateway of last resort is not set10.0.0.0 255.255.255.0 is subnetted, 2 subnetsO 10.2.1.0 [110/10] via 10.64.0.2, 00:00:50, Ethernet0

The show ip ospf interface CommandRouterA# show ip ospf interface e0 Ethernet0 is up, line protocol is up Internet Address 10.64.0.1/24, Area 0 Process ID 1, Router ID 10.64.0.1, Network Type BROADCAST, Cost: 10 Transmit Delay is 1 sec, State DROTHER, Priority 1 Designated Router (ID) 10.64.0.2, Interface address 10.64.0.2 Backup Designated router (ID) 10.64.0.1, Interface address 10.64.0.1 Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 Hello due in 00:00:04 Neighbor Count is 1, Adjacent neighbor count is 1 Adjacent with neighbor 10.64.0.2 (Designated Router) Suppress hello for 0 neighbor(s)

The show ip ospf neighbor CommandRouterB# show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface10.64.1.1 1 FULL/BDR 00:00:31 10.64.1.1 Ethernet010.2.1.1 1 FULL/- 00:00:38 10.2.1.1 Serial0

show ip ospf neighbor detailshow ip ospf database

Setting Priority for DR Electionip ospf priority numberThis interface configuration command assigns the OSPF priority to an interface.Different interfaces on a router may be assigned different values.The default priority is 1. The range is from 0 to 255.0 means the router is a DROTHER; it cant be the DR or BDR.Router(config-if)#

EIGRPIGRPDVEasy to configureNeighborAdvanced MetricPeriodicBroadcastOSPFLSIncremental UpdatesMulticast Open StandardEIGRPHybridDUALTopology DatabaseRapid ConvergenceReliable

OverviewEnhanced Interior Gateway Routing Protocol (EIGRP) is a Cisco-proprietary routing protocol based on Interior Gateway Routing Protocol (IGRP).

Released in 1994, Unlike IGRP, which is a classful routing protocol, EIGRP supports CIDR and VLSM.

it is probably one of the two most popular routing protocols in use today.

Compared to IGRP, EIGRP boasts faster convergence times, improved scalability, and superior handling of routing loops.

EIGRP is often described as a hybrid routing protocol, offering the best of distance vector and link-state algorithms.

Comparing EIGRP with IGRPIGRP and EIGRP are compatible with each other. EIGRP offers multiprotocol support, but IGRP does not. Communication via Reliable Transport Protocol (RTP)Best path selection via Diffusing Update Algorithm (DUAL)Improved convergence timeReduced network overhead

Introducing EIGRPEIGRP supports:Rapid convergenceReduced bandwidth usageMultiple network-layer protocols

EIGRP TablesEIGRP maintains 3 tables

Neighbor table Topology table Routing table

Neighbor DiscoveryThere are three conditions that must be met for neighborship establishmentHello or ACK receivedAS numbers matchIdentical metrics (K values)

Hello? AS? KK1 BWK2- DelayK3-LoadK3-ReliabilityK5-MTU

Metric CalculationThe metrics used by EIGRP in making routing decisions are (lower the metric the better):bandwidthdelayloadReliabilityMTU

By default, EIGRP uses only:BandwidthDelay

Analogies:Think of bandwidth as the width of the pipe anddelay as the length of the pipe.

Bandwidth is the carrying capacityDelay is the end-to-end travel time.

Neighbor TableThe neighbor table is the most important table in EIGRP

Stores address and interface of neighbor

Topology TableGive me information about all routesNetwork

Topology TableThe topology table is made up of all the EIGRP routing tables in the autonomous system.

DUAL takes the information and calculates the lowest cost routes to each destination.

By tracking this information, EIGRP routers can identify and switch to alternate routes quickly.

The information that the router learns from the DUAL is used to determine the successor route, which is the term used to identify the primary or best route.

Every EIGRP router maintains a topology table. All learned routes to a destination are maintained in the topology table.

Routing TablesA successor is a route selected as the primary route to use to reach a destination.DUAL calculates Successor (Primary Route) and places it in the routing table (and topology table) Can have up to 4 successors of equal or unequal valueDUAL calculates Feasible Successor (Backup Route) and places it in the Topology Table.Promoted to successor if the route goes down if it has a lower cost than current successorIf no FS in Table - Send query Multiple feasible successors for a destination can be retained in the topology table although it is not mandatory

EIGRP Concepts & TerminologyEIGRP routers that belong to different autonomous systems (ASes) dont automatically share routing information

The only time EIGRP advertises its entire routing table is when it discovers a new neighbor and forms an adjacency with it through the exchange of Hello packets

When this happens, both neighbors advertise their entire routing tables to one another

After each has learned its neighbors routes, only changes to the routing table are propagated

172.16.100.01.544Mbps56Kbps1.544MbpsDist to 172.16.100.0 =100Dist to 172.16.100.0 =100Dist to 172.16.100.0 =35010Mbps10Mbps 1001,544Mbps 25056Kbps -1000Chennai receives an update from Mumbai with a cost of 100, which is Mumbai's cost to reach 172.16.100.0, This cost is referred to as the reported distance (RD)Bangalore will report its cost to reach 172.16.100.0. Bangalore's RD is 350Chennai will compute its cost to reach 172.16.100.0 via Mumbai and Bangalore and compare the metrics for the two pathsChennai's cost via Mumbai is 1100. Chennai's cost via Bangalore is 600. The lowest cost to reach a destination is referred to as the feasible distance (FD) for that destination Chennai's FD to 172.16.100.0 is 600. The next-hop router in the lowest-cost path to the destination is referred to as the successor. A feasible successor is a path whose reported distance is less than the feasible distance, and it is considered a backup route.

EIGRP TermsFeasible distance (FD) - This is the lowest calculated metric to reach destination. This is the route that you will find in the routing table, because it is considered the best path

Reported distance (RD) - The distance reported by an adjacent neighbor to a specific destination.

Interface information - The interface through which the destination can be reached.

Route status - The status of a route. Routes are identified as being either passive, which means that the route is stable and ready for use, or active, which means that the route is in the process of being recomputed by DUAL

EIGRP Terminology and OperationsSuccessor Current RouteA successor is a route selected as the primary route to use to reach a destination. Successors are the entries kept in the routing table.

Feasible Successor - A backup routeA feasible successor is a backup route. These routes are selected at the same time the successors are identified, but they are kept in the topology table. Multiple feasible successors for a destination can be retained in the topology table.

Reliable Transport Protocol (RTP)Used by EIGRP for its routing updates in place of TCPEIGRP can call on RTP to provide reliable or unreliable service EIGRP uses reliable service for route updatesUnreliable for Hellos

Reliable Transport Protocol (RTP) is a transport layer protocol that guarantees ordered delivery of EIGRP packets to all neighbors. On an IP network, hosts use TCP to sequence packets and ensure their timely delivery. RIP uses UDPHowever, EIGRP is protocol-independent and does not rely on TCP/IP to exchange routing information the way that RIP, IGRP, and OSPF do. EIGRP uses RTP as its own proprietary transport layer protocol to guarantee delivery of routing information.With RTP, EIGRP can multicast and unicast to different peers simultaneously.

Diffusing Update Algorithm (DUAL)All route computations in EIGRP are handled by DUALOne of DUAL's tasks is maintaining a table of loop-free paths to every destination. This table is referred to as the topology table DUAL saves all paths in the topology table The least-cost path(s) is copied from the topology table to the routing table In the event of a failure, the topology table allows for very quick convergence if another loop-free path is available If a loop-free path is not found in the topology table, a route recomputation must occur DUAL queries its neighbors, who, in turn, may query their neighbors, and so on... Hence the name "Diffusing" Update Algorithm

VLSM SupportEIGRP supports the use of Variable- Length Subnet Masks

Can use 30-bit subnet masks for point-to-point networks

Because the subnet mask is propagated with every route update, EIGRP also supports the use of discontiguous subnets

Discontiguous network is the one that has two or more subnetworks of a classful network connected together by different classful networks

Discontiguous Network

EIGRP & IGRP Metric Calculation

Configuring EIGRPRouter(config-router)#network network-numberSelects participating attached networksRouter(config)#router eigrp autonomous-systemDefines EIGRP as the IP routing protocol

EIGRP Configuration Example

EIGRP Configuration 200.0.0.17200.0.0.9200.0.0.10200.0.0.13200.0.0.14200.0.0.33200.0.0.18200.0.0.34255.255.255.240 255.255.255.252 255.255.255.252 255.255.255.224 R1#config tEnter configuration commands, one per line. End with CNTL/Z.R1(config)#router eigrp 10R1(config-router)#network 200.0.0.16R1(config-router)#network 200.0.0. 8R1(config-router)#^ZR3#config tEnter configuration commands, one per line. End with CNTL/Z.R3(config)#router eigrp 10R3(config-router)#network 200.0.0. 32 R3(config-router)#network 200.0.0. 12 R3(config-router)#^Z

Verifying the EIGRP ConfigurationTo verify the EIGRP configuration a number of show and debug commands are available.

These commands are shown on the next few slides.

show ip eigrp topologyshow ip eigrp topology[active | pending | successors]

show ip eigrp topologyall-linksshow ip eigrp traffic

Administrative Distances

TELNETGetting information about remote deviceCan connect to remote device and configure a devicePassword must be set R1(config)# line vty 0 4Password cisco login

2002, Cisco Systems, Inc. All rights reserved.*Discovering Neighbors on the Network

Cisco Discovery Protocol CDP is a proprietary utility that gives you a summary of directly connected switches, routers, and other Cisco devices. CDP discovers neighboring devices regardless of which protocol suite they are running.Runs on the Data link layerPhysical media must support the Subnetwork Access Protocol (SNAP) encapsulation.Only give directly connected deviceBy default enabled, you can enable or disable

Discovering Neighbors with CDPCDP runs on routers with Cisco IOS software Release 10.3 or later and on Cisco switches.Show CDP ?Summary information includes:Device IDLocal Interface Port IDCapabilities listPlatform

CDP CDP timer is how often CDP packets are transmitted to all active interfaces.

Router(config)#cdp timer 90

CDP holdtime is the amount of time that the device will hold packets received from neighbor devices.Router(config)#cdp holdtime 240

Using CDP

Using the show cdp neighbors CommandThe show cdp neighbor command (sh cdp nei for short) delivers information about directly connected devices.

CDPshow cdp neighbor detail

This command can be run on both routers and switches, and it displays detailed information about each device connected to the device

Using the show cdp entry CommandThe show cdp entry * command displays the same information as the show cdpneighbor details command.

Additional CDP CommandsThe show cdp traffic command displays information about interface traffic, including the number of CDP packets sent and received and the errors with CDP.

CDP CommandsTo disable the CDP on particular interface use the "no cdp enable" command

To disable CDP on the entire router use the "no cdp run" in global configuration mode.

SummaryCisco Discovery Protocol is an information-gathering tool used by network administrators to get information about directly connected devices.

CDP exchanges hardware and software device information with its directly connected CDP neighbors.

You can enable or disable CDP on a router as a whole or on a port-by-port basis.

The show cdp neighbors command displays information about a routers CDP neighbors.

The show cdp entry, show cdp traffic, and show cdp interface commands display detailed CDP information on a Cisco device.

Why Use Access Lists?Manage IP traffic as network access growsFilter packets as they pass through the router

What are ACLs?ACLs are lists of conditions that are applied to traffic traveling across a router's interface.

These lists tell the router what types of packets to accept or deny.

Acceptance and denial can be based on specified conditions.

ACLs can be configured at the router to control access to a network or subnet.

Some ACL decision points are source and destination addresses, protocols, and upper-layer port numbers.

Reasons to Create ACLsThe following are some of the primary reasons to create ACLs:

Limit network traffic and increase network performance. Provide traffic flow control. Provide a basic level of security for network access. Decide which types of traffic are forwarded or blocked at the router interfacesFor example: Permit e-mail traffic to be routed, but block all telnet traffic. If ACLs are not configured on the router, all packets passing through the router will be allowed onto all parts of the network.

ACLsDifferent access list for TelnetWhen configuring ISDN you need to use access listImplicit deny at bottomAll restricted statements should be on firstThere are two typesStandardExtended

NetworkN1N2N3N4N5N6192.168.12.0ABC192.168.34.0192.168.56.0192.168.12.2192.168.12.3

IP PacketSRC IP AddressDEST IP AddressProtocol typeSRC PortDEST PortThe first 2 bytes in the TCP/UDP header are the source port numberThe next 2 bytes in the TCP/UDP header are the Destination port number

StandardChecks source addressPermits or denies entire protocol suiteExtendedChecks source and destination addressGenerally permits or denies specific protocolsTypes of Access Lists

How to Identify Access ListsStandard IP lists (1-99) test conditions of all IP packets from source addresses.Extended IP lists (100-199) test conditions of source and destination addresses, specific TCP/IP protocols, and destination ports.Standard IP lists (1300-1999) (expanded range).Extended IP lists (2000-2699) (expanded range).

Standard ACLsThe full syntax of the standard ACL command is:

Router(config)#access-list access-list-number {deny | permit} source [source-wildcard ]

The no form of this command is used to remove a standard ACL. This is the syntax:Router(config)#no access-list access-list-numberConfig# Access-list 1 deny 192.168.1.0 0.0.0.255Config# access-list 1 permit any

Wildcard Mask Access-list 99 permit 192.168.1.1 wildcard maskAll 32 bits of an IP Address can be filteredWildcard inverse mask0=must match1= ignore

The ANY and HOST keywordAccess-list 1 permit 200.0.0.9 0.0.0.0Orpermit host 200.0.0.9Access-list 1 permit 0.0.0.0 255.255.255.255Orpermit any

Testing Packets with Standard Access Lists

Outbound ACL OperationIf no access list statement matches, then discard the packet.

Reading an ACLFirst Hit or Best Fit?Access-list 99 deny host 192.168.1.1 0.0.0.0access-list 99 permit any255.255.255.255

Access-list 99 permit 192.168.1.0 0.0.0.255Access-list 99 deny host 192.168.1.1access-list 99 permit any

Access-list 99 deny host 192.168.1.1

Implicit deny at the end of every ACL

Creating ACLsACLs are created in the global configuration mode. There are many different types of ACLs including standard, extended, IPX, AppleTalk, and others. When configuring ACLs on a router, each ACL must be uniquely identified by assigning a number to it. This number identifies the type of access list created and must fall within the specific range of numbers that is valid for that type of list. Since IP is by far the most popular routed protocol, addition ACL numbers have been added to newer router IOSs. Standard IP: 1300-1999Extended IP: 2000-2699

The ip access-group command

Exercise Standard Access ListAccount should be denied access to Sales

To steps to configureCreate a standard Access listApply ACL to proper interface inbound or outboundS0S0E0E0192.168.0.18255.255.255.248S0S1192.168.0.17255.255.255.248192.168.0.5255.255.255.252192.168.0.6255.255.255.252192.168.0.9255.255.255.252192.168.0.10255.255.255.252192.168.0.33255.255.255.240192.168.0.34255.255.255.240

Exercise Standard Access ListS0S0E0E0192.168.0.18255.255.255.248S0S1192.168.0.17255.255.255.248192.168.0.5255.255.255.252192.168.0.6255.255.255.252192.168.0.9255.255.255.252192.168.0.10255.255.255.252192.168.0.33255.255.255.240192.168.0.34255.255.255.240Config# Access-list 1 deny 192.168.0.18 0.0.0.7Config# access-list 1 permit any Config#int e 0 Config-if# ip access-group 1 out

Extended ACLsExtended ACLs are used more often than standard ACLs because they provide a greater range of control.

Extended ACLs check the source and destination packet addresses as well as being able to check for protocols and port numbers.

At the end of the extended ACL statement, additional precision is gained from a field that specifies the optional Transmission Control Protocol (TCP) or User Datagram Protocol (UDP) port number.

Logical operations may be specified such as, equal (eq), not equal (neq), greater than (gt), and less than (lt), that the extended ACL will perform on specific protocols.

Extended ACLs use an access-list-number in the range 100 to 199 (also from 2000 to 2699 in recent IOS).

ConfigurationAccess-list acl# {permit/Deny}ProtocolSrc IP src WCMDst IP dst WCMOpetrator portProtocolOSPFEIGRPICMPTCPUDPRPIf you need to Block a routing protocolIPOperatoreqgtltneq

Testing Packets with Extended Access Lists

Extended ACL Syntax

Extended ACL LABAccount should be denied Sales Web siteConfig# Access-list 100 deny tcp 200.0.0.10 0.0.0.7 200.0.0.18 0.0.0.15 eq wwwConfig# access-list 100 permit IP any anyConfig#int Fastethernet 0/0 Config-if# ip access-group 100 IN

Extended ACL LAB -2192.168.0.34 should be denied FTP of 192.168.0.18

On Router R1Config# Access-list 100 deny tcp 192.168.0.34 0.0.0.0 192.168.0.18 0.0.0.0 eq 21Config# access-list 100 permit IP any any

Config#int s0Config-if# ip access-group 100 INS0S0E0E0192.168.0.18 should be denied website of 192.168.0.34

On Router R3Config# Access-list 100 deny tcp 192.168. 0.18 0.0.0.0 192.168.0.34 0.0.0.0 eq 80Config# access-list 100 permit IP any any

Config#int s0Config-if# ip access-group 100 INS1S0192.168.0.18255.255.255.248192.168.0.17255.255.255.248192.168.0.5255.255.255.252192.168.0.6255.255.255.252192.168.0.9255.255.255.252192.168.0.10255.255.255.252192.168.0.33255.255.255.240192.168.0.34255.255.255.240

Deny FTPaccess-list 101 deny tcp any any eq 21

access-list 101 permit ip any any

or

access-list 101 deny tcp any any eq ftp

access-list 101 permit ip any any

RulesFor extended access list apply near to the sourceFor standard access list apply near to the destination

Named ACLsIP named ACLs were introduced in Cisco IOS Software Release 11.2, allowing standard and extended ACLs to be given names instead of numbers.

The characteristics of named accesslist: Identify an ACL using an alphanumeric name. You can delete individual statements in a named access list Named access lists must be specified as standard or extendedYou can use the ip access-list command to create named access lists.

Named ACLs are not compatible with Cisco IOS releases prior to Release 11.2.

The same name may not be used for multiple ACLs.

Named ACLsNumbered Access list did not give you any hint, What is filtered

Named ACLs are both basic and advanced filtering tool

Name cannot start with a number or !

Cannot have space in the name

Should not have ? Character anywhere in the name

Name is case sensitive

Named ACL ExampleR1(config)#ip access-list standard blocksalesR1(config-std-nacl)#deny 172.16.40.0 0.0.0.255R1(config-std-nacl)#permit anyR1(config-std-nacl)#exitR1(config)#^ZR1#

#Int e 0#Ip access-group blocksales out

Verify Access List

Basic Rules for ACLsStandard IP access lists should be applied closest to the destination. Extended IP access lists should be applied closest to the source. Use the inbound or outbound interface reference as if looking at the port from inside the router. Statements are processed sequentially from the top of list to the bottom until a match is found, if no match is found then the packet is denied. There is an implicit deny at the end of all access lists. This will not appear in the configuration listing. Access list entries should filter in the order from specific to general. Specific hosts should be denied first, and groups or general filters should come last. Never work with an access list that is actively applied. New lines are always added to the end of the access list. A no access-list x command will remove the whole list. It is not possible to selectively add and remove lines with numbered ACLs. Outbound filters do not affect traffic originating from the local router.

DV- the router D will tell C that I know network X, and C will tell B that I know network X and so on, route A does not know anything beyond its neighbor, so its routing by tumor. This also uses periodic update, it also sends the entire routing table, these protocls are based in the early days of internet and some of them are class based.Link state gives much more information, here the link is defined with its interface, IP address, Mask, the type of network its on and its neighbors SO Router A will tell My IP. This information is passed to router to router and maintain two databases.The topology table is important and its because of topology table the robustness comes. The topology table contains Link state advertisements and the router knows the network topology, any network fails the convergence is faster.

DV will send entire routing table will waste the bandwidth. Link states exchange updates about only Link statesSuitable for very large networksDraw diagram to explain router IDIf the two routers are the only routers on the network, an adjacency should form. If there are more than two routers on the network, adjacencies only form with the designated router (DR) and backup designated router (BDR). If the two routers have already formed adjacencies with the DR and the BDR, they cannot form adjacencies with each other Backbone Router: Has an interface connected to the backbone (Area 0). Area Border Router (ABR): Has interfaces in multiple areas with at lest one interface in area 0. Connects other areas to the backbone and maintains routing information for each connected area. Autonomous System Boundary Router (ASBR): Router located between OSPF autonomous system and a non-OSPF network. Used to redistribute routing information between networks. Must reside in a non-stub area. OSPF routers and links are grouped logically into areas that are identified by assigned numbers. All OSPF networks have at least one area with the default being area 0. If more than one area exists, area 0 is defined as the backbone area and is used to connect all other areas. Each area has its own link state databases. Area 0 should not have more than 30 routersIn order to ensure that a router will become the OSPF DR for any given segment, there are a number of options. One way is to manually configure the interface priority as described in option A above using the "ip ospf priority" interface configuration command. The second method is described in option C. OSPF routers will always use the loopback interface IP address as the router ID, when configured, and the router with the highest IPaddress will be chosen as the DR when the priorities are the same. The final method is to change the priority of the other routers in the segment to zero. When the OSPF priority is set to 0, the router is ineligible to become the DR or the BDR. Important Note: The OSPF DR/BDR election process is not pre-emptive, so any changes to the network regarding the DR/BDR election process will only occur when the routers are restarted.When the OSPF process starts, the Cisco IOS uses the highest local active IP address asits OSPF router ID. If there is no active interface, the OSPF process will not start. If theactive interface goes down, the OSPF process has no router ID and therefore ceases tofunction until the interface comes up again.

EIGRP scales the metric of IGRP by a factor of 256. That is because EIGRP uses a metric that is 32 bits long, and IGRP uses a 24-bit metric. EIGRP can multiply or divide by 256 to easily exchange information with IGRP

Purpose: The figure introduces the IGRP routing protocol. IGRP is a sophisticated distance vector routing protocol.Emphasize: The Interior Gateway Routing Protocol (IGRP) is a dynamic distance-vector routing protocol designed by Cisco in the mid-1980s for routing in an autonomous system that contains large, arbitrarily complex networks with diverse bandwidth and delay characteristics. Historically, IGRP became one of the success factors for the early Cisco IOS software capabilities because of its superiority to RIP version 1.The important IGRP characteristics are as follows:More scalability than RIP Fast response to network changesSophisticated metricMultiple-path support

EIGRP MetricsAnother really sweet thing about EIGRP is that unlike many other protocols that use a singlefactor to compare routes and select the best possible path, EIGRP can use a combination of four:

Bandwidth

Delay

Load

ReliabilityEIGRP routers that belong to different autonomous systems (ASes) dont automatically share routing information and they dont become neighbors. This behavior can be a real benefit when used in larger networks to reduce the amount of route information propagated through a specific AS. The only catch is that you might have to take care of redistribution between the different ASes manually.The only time EIGRP advertises its entire routing table is when it discovers a new neighbor and forms an adjacency with it through the exchange of Hello packets. When this happens, both neighbors advertise their entire routing tables to one another. After each has learned its neighbors routes, only changes to the routing table are propagated from then on.When EIGRP routers receive their neighbors updates, they store them in a local topology table. This table contains all known routes from all known neighbors, and serves as the raw material from which the best routes are selected and placed into the routing table.

EIGRP routers keep route and topology information readily available in RAM, so they can react quickly to changes.

Like OSPF, EIGRP saves this information in several tables and databases.

Route source - The identification number of the router that originally advertised that route. This field is populated only for routes learned externally from the EIGRP network.

Reliable Transport ProtocolThe EIGRP transport mechanism uses a mix of multicast and unicast packets, using reliable delivery when necessary. All transmissions use IP with the protocol type field set to 88. The IP multicast address used is 224.0.0.10. DUAL requires guaranteed and sequenced delivery for some transmissions. This is achieved using acknowledgments and sequence numbers. So, for example, update packets (containing routing table data) are delivered reliably (with sequence numbers) to all neighbors using multicast. Acknowledgment packets--with the correct sequence number--are expected from every neighbor. If the correct acknowledgment number is not received from a neighbor, the update is retransmitted as a unicast. The sequence number (seq num) in the last packet from the neighbor is recorded to ensure that packets are received in sequence. The number of packets in the queue that might need retransmission is shown as a queue count (QCnt), and the smoothed round trip time (SRTT) is used to estimate how long to wait before retransmitting to the neighbor. The retransmission timeout (RTO) is the time the router will wait for an acknowledgment before retransmitting the packet in the queue. Some transmissions do not require reliable delivery. For example, hello packets are multicast to all neighbors on an Ethernet segment, whereas acknowledgments are unicast. Neither hellos nor acknowledgments are sent reliably. EIGRP also uses queries and replies as part of DUAL. Queries are multicast or unicast using reliable delivery, whereas replies are always reliably unicast. Query and reply packets are discussed in more detail in the next section. All route computations in EIGRP are handled by DUAL. One of DUAL's tasks is maintaining a table of loop-free paths to every destination. This table is referred to as the topology table. Unlike traditional DV protocols that save only the best (least-cost) path for every destination, DUAL saves all paths in the topology table. The least-cost path(s) is copied from the topology table to the routing table. In the event of a failure, the topology table allows for very quick convergence if another loop-free path is available. If a loop-free path is not found in the topology table, a route recomputation must occur, during which DUAL queries its neighbors, who, in turn, may query their neighbors, and so on... hence the name "Diffusing" Update Algorithm. Slide 1 of 2Purpose: This figure explains how to use the router igrp and network commands to configure an IGRP process.Emphasize: Note that the AS keyword is required for IGRP.You can use multiple network commands to specify all networks that are to participate in the IGRP process. Only those networks specified will be published to other routers.

Purpose: The figure shows how the IGRP commands operate on the example network.Emphasize: An administrator only specifies directly connected networks that should be published to other routers.Without the network command, nothing is advertised. With a network command, the router will advertise every subnet within the Class A, B, or C network specified in the configuration.# Show users will show connected users# Clear line 1 will disconnect the session on line 1

Purpose: This chapter introduces the Cisco IOS CLI on the Catalyst 1900 switch and router. Timing: This chapter should take about 2 hours to present.Note: The Catalyst 1900 switch only has a subset of the router Cisco IOS commands available.Contents: Introduction to Cisco IOS. Explain to the student what is IOS?Cisco Device startup procedures in general. IOS configuration source.General introduction to the IOS CLI.Cat 1900 switch startup procedures.Intro to Cat 1900 CLI. This part covers the basic configuration on the switch, like setting the IP address and hostname. More details about the various Cat 1900 switch configuration commands are explained in Chapter 6 and 7. Router startup procedures. More details on the router startup process is discussed in chapter 5. Router IOS CLI. Note: CDP is sent using multicast frames with the MAC address 0100.0ccc.cccc.CDP is a Cisco proprietary data link layer protocol that operates over any medium that supports the Subnetwork Access Protocol (SNAP) encapsulation (LANs, most WANs, and ATM). It is important to understand that because CDP operates at Layer 2 (data link layer of the OSI model), it functions independently of the Layer 3 (network) protocol (IP or IPX). CDP is on by default, but it can be disabled. In many cases, CDP is disabled on dial backup links, such as ISDN, so as to not keep the link up constantly.

CDP One dependency, the media type at the physical layer must support SNAP. SNAP was created because all protocols does not work well for 802.3 Ethernet frame as 802.3 had no type filed any longer. The original Ethernet had type filed, But the 802.3 had replaced this with length field, so When we bring SNAP at layer 2 it brings back type field. Frame relay, Ethernet, ATM, Token ring all support SNAPDevice ID. The hostname of the neighboring deviceLocal Interface. The interface on which this router received information about the neighboring device. Holdtime. The amount of time the router will store this information before dropping it from memory, if additional CDP packets are not received. Capability. The type of device that announced itself using CDP.Platform. The hardware platform of the neighboring equipment.Port ID. The port from which the CDP packet was sent on the neighboring device.

Emphasize: CDP is media- and protocol-independent and runs on all Cisco-manufactured equipment including routers, access servers, switches, and some managed hubs. With CDP, network management applications can retrieve the device type and SNMP agent address of neighboring devices. This capability enables applications to send SNMP queries to neighboring devices. CDP allows network management applications to dynamically discover Cisco devices that are neighbors. CDP runs on all media that support the Subnetwork Access Protocol, including LAN and Frame Relay. CDP runs over the data link layer only, not the network layer. Therefore, two systems that support different network-layer protocols can learn about each other.Cached CDP information is available to network management applications. Cisco devices never forward a CDP packet. When new information is received, old information is discarded. The holdtime determines how long to keep existing information from a neighbor.

Note: Some of the CDP commands are not available on the Catalyst 1900 switch, like cdp run, show cdp traffic, and show cdp entry.

Its important to remember that CDP packets arent passed through a Ciscoswitch, and that you see only whats directly attached. So this means that if your router is connected to a switch, you wont see any of the devices hooked up to that switch.Emphasize: This graphic shows the show cdp neighbors command initiated from a router, which displays a summary of the capabilities and access details for the CDP neighbors. The show cdp neighbors detail command shows detailed information about the same devices. Note: If the neighbor is a Catalyst 1900 switch, the switch MAC address is also displayed. If the switch is a 2900xl, its MAC address is not displayed.Device ID. The hostname of the neighboring deviceLocal Interface. The interface on which this router received information about the neighboring device. Holdtime. The amount of time the router will store this information before dropping it from memory, if additional CDP packets are not received. Capability. The neighbors capability, such as router, switch, or repeater. The capability codes are listed at the top of the command output.Platform. The hardware platform of the neighboring equipment.(Cisco 2509, Cisco 2511, andCatalyst 5000)Port ID. The port from which the CDP packet was sent on the neighboring device.

Emphasize: The example shows what information can be obtained about RouterAs neighbor. CDP is one way to learn about other Cisco devices on the network.

Note: The holdtime indicates how long the neighbor information will be kept in the local CDP table. 181-37Purpose: This slide discuss the initial configurations on the routers and switches. Note: There is no setup mode on the Catalyst 1900 switch. Layer 2 of 2Emphasize: An access list is a mechanism for identifying particular traffic. One application of an access list is for filtering traffic into or out of a router interface.

Permission for routerManage IP TrafficFilter packet which pas thruEither can permit or DenyIf u want to permit only one from a network then permit shud be firstLayer 3 of 3Purpose: Describe an inbound versus outbound access list on an interface.Layer 3 of 3Emphasize: Layer 3Adds the Novell IPX access lists covered in Chapter 11, Configuring Novell IPX, and the number ranges for these types of access lists. As of Release 11.2.4(F), IPX also supports named access lists.Point out that number ranges generally allow 100 different access lists per type of protocol. When a given hundred-number range designates a standard access list, the rule is that the next hundred-number range is for extended access lists for that protocol. Exceptions to the numbering classification scheme include AppleTalk and DECnet, where the same number range can identify various access list types. For the most part, number ranges do not overlap between different protocols. Note: With Cisco IOS 12.0, the IP access-lists range has been expanded to also include: IP standard access list (expanded range) IP extended access list (expanded range) Purpose: This graphic gives an overview of the type of TCP/IP packet tests that standard access lists can filter. It uses the encapsulation graphic and diamond decision graphic to remind students of material presented earlier in this course.

Layer 3 of 3Purpose: Shows a deny result of the access list test. Emphasize: Now the packet is discarded into the packet discard bucket. The unwanted packet has been denied access to the outbound interface. The Notify Sender message shows a process like ICMP, returning an administratively prohibited message back to the sender.

Explain how the access list process, here there are three ACLS. Can give the example with a host IP address 192.168.1.1 and host 192.168.1.2 what happens on all the three ACLSPurpose: This graphic gives an overview of the type of TCP/IP packet tests that extended access lists can filter. It uses the encapsulation graphic and diamond decision graphic to remind students of material presented earlier in this course.

Named access lists allow you to use names to both create and apply either standard orextended access lists. There is nothing new or different about these access lists aside from beingable to refer to them in a way that makes sense to humans.