Introduction to Local and Wide Area Networks

Transcription

1 Introduction to Local and Wide Area Networks Lecturers Amnach Khawne Jirasak Sittigorn Chapter 1 1

2 Routing Protocols and Concepts Chapter 8 : The Routing Table: A Closer Look Chapter 9 : EIGRP Chapter 1 2

3 The Routing Table: A Closer Look Routing Protocols and Concepts Chapter 8 Chapter 1 3

4 Objectives Describe the various route types found in the routing table structure Describe the routing table lookup process. Describe routing behavior in routed networks. Chapter 1 4

5 Introduction Chapter Focus -Structure of the routing table -Lookup process of the routing table -Classless and classful routing behaviors Chapter 1 5

6 Routing Table Structure Lab Topology 3 router setup -R1 and R2 share a common /16 network with /24 subnets. -R2 and R3 are connected by the / network. -R3 also has a /24 subnet, which is disconnected, or discontiguous, from the network that R1 and R2 share. Chapter 1 6

7 Routing Table Structure Routing table entries come from the following sources -Directly connected networks -Static routes -Dynamic routing protocols Chapter 1 7

8 Routing Table Structure t Level 1 Routes As soon as the no shutdown command is issued the route is added to routing table Chapter 1 8

9 Routing Table Structure Cisco IP routing table is a hierarchical structure -The reason for this is to speed up lookup process Chapter 1 9

10 Routing Table Structure t Level 1 Routes -Have a subnet mask equal to or less than the classful mask of the network address. Level 1 route can function as -Default route -Supernet route -Network route Chapter 1 10

11 Routing Table Structure t Level 1 Routes -Ultimate Route Includes either: -A next-hop address OR -An exit interface Chapter 1 11

12 Routing Table Structure Parent and Child Routes -A parent route is a level e 1 route -A parent route does not contain any next- hop IP address or exit interface information Chapter 1 12

13 Routing Table Structure t Automatic creation of parent routes -Occurs any time a subnet is added to the routing table Child routes -Child routes are level 2 routes -Child routes are a subnet of a classful network address Chapter 1 13

14 Routing Table Structure t Level 2 child routes contain route source & the network address of the route Level 2 child routes are also considered ultimate routes Reason: they contain the next hop address &/or exit interface Chapter 1 14

15 Routing Table Structure Both child routes have the same subnet mask -This means the parent route maintains i the /24 mask 2 Chapter 1 15

16 Routing Table Structure Diagram illustrates 2 child networks belonging to the parent route / 24 Chapter 1 16

17 Routing Table Structure In classless networks, child routes do not have to share the same subnet mask Chapter 1 17

18 Routing Table Structure t Parent & Child Routes: Classless Networks Network Type Parent route s Classful mask is Displayed Term variably subnetted is seen in parent route in routing table Includes the # of different masks of child routes Subnet mask included with each child route entry Class- No No No No ful Class- Yes Yes Yes Yes less Chapter 1 18

19 Routing Table Structure Parent & Child Routes: Classless Networks Chapter 1 19

20 Routing Table Lookup Process The Route Lookup Process Examine level 1 routes -If best match a level 1 ultimate route and is not a parent route this route is used to forward packet Router examines level 2 (child) routes -If there is a match with level 2 child route then that subnet is used to forward packet -If no match then determine routing behavior type Router determines classful or classless routing behavior -If classful then packet is dropped -If classless then router searches level one supernet and default routes -If there exists a level 1 supernet or default route match then Packet is forwarded. If not packet is dropped Chapter 1 20

21 Routing Table Lookup Process Longest Match: Level 1 Network Routes Best match is also known as the longest match The best match is the one that has the most number of left most bits matching between the destination IP address and the route in the routing table. Chapter 1 21

22 Routing Table Lookup Process Finding the subnet mask used to determine the longest match Scenario: PC1 pings Router examines level 1 route for best match There exist a match between & / 24 Router forwards packets out s0/0/0 Chapter 1 22

23 Routing Table Lookup Process The process of matching -1st there must be a match made between the parent route & destination IP -If a match is made then an attempt at finding a match between the destination IP and the child route is made. Chapter 1 23

24 Routing Table Lookup Process Finding a match between packet s destination IP address and the next route in the routing table -The figure shows a match between the destination IP of and the level one IP of / 24 then packet forwarded out s0/0/0 Chapter 1 24

25 Routing Table Lookup Process Level 1 Parent & Level 2 Child Routes Before level 2 child routes are examined -There must be a match between classful level one parent route and destination IP address. Chapter 1 25

26 Routing Table Lookup Process After the match with parent route has been made Level 2 child routes will be examined for a match -Route lookup process searches for child routes with a match with destination IP Chapter 1 26

27 Routing Table Lookup Process Chapter 1 27

28 Routing Table Lookup Process How a router finds a match with one of the level 2 child routes -First router examines parent routes for a match -If a match exists then: Child routes are examined Child route chosen is the one with the longest match Chapter 1 28

29 Routing Table Lookup Process Example: Route Lookup Process with VLSM -The use of VLSM does not change the lookup process -If there is a match between destination IP address and the level 1 parent route then -Level 2 child routes will be searched Chapter 1 29

30 Routing Behavior Classful & classless routing gprotocols Influence how routing table is populated Classful & classless routing behaviors Determines how routing table is searched after it is filled Chapter 1 30

31 Routing Behavior Classful Routing Behavior: no ip classless What happens if there is not a match with any level l 2 child routes of the parent? -Router must determine if the routing behavior is classless or classful -If router is utilizing classful routing behavior then -Lookup process is terminated and packet is dropped Chapter 1 31

32 See Next Page Chapter 1 32 Routing Behavior Classful Routing Behavior Search Process An example of when classful routing behavior is in effect and why the router drops the Packet -The destination s subnet mask is a /24 and none of the child routes left most bits match the first 24 bits. This means packet is dropped

33 Chapter 1 33

34 Routing Behavior Classful Routing Behavior Search Process The reason why the router will not search beyond the child routes Originally networks were all classful This meant an organization could subnet a major network address and enlighten all the organization s routers about the subnetting Therefore, if the subnet was not in the routing table, the subnet did not exist and packet was dropped Chapter 1 34

35 Routing Behavior ip Classless Beginning with IOS 11.3, ip classless was configured by default Classless routing behavior works for -Discontiguous networks And -CIDR supernets Chapter 1 35

36 Routing Behavior Classless l Routing Behavior: ip classless l Route lookup pprocess when ip classless is in use -If classless routing behavior in effect then Search S h level l 1 routes Supernet routes Checked first -If a match exists then forward packet Default routes Checked second If there is no match or no default route then the Packet is dropped Chapter 1 36

37 Routing Behavior Classless Routing Behavior Search Process Router begins search process by finding a match between destination IP and parent route After finding the above mentioned match, then there is a search of the child route Chapter 1 37

38 Routing Behavior Classless Routing Behavior Search Process If no match is found in child routes of previous slide then Router continues to search the routing table for a match that may have fewer bits in the match Chapter 1 38

39 Routing Behavior Classful vs. Classless Routing Behavior -It is recommended to use classless routing behavior Reason: so supernet and default routes can be used whenever needed Chapter 1 39

40 Summary Content/structure of a routing table Routing table entries es -Directly connected networks -Static route -Dynamic routing protocols Routing tables are hierarchical -Level 1 route Have a subnet mask that is less than or equal to classful subnet mask for the network address -Level 2 route These are subnets of a network address Chapter 1 40

41 Summary Routing table lookup process Begins with examining level 1 routes for best match with packet s destination IP If the best match = an ultimate route then -Packet is forwarded -Else- -Parent route is examined If parent route & destination IP match then Level 2 (child) routes are examined Level 2 route examination If a match between destination IP and child route found then Packet forwarded d -Else If Router is using classful routing behavior then Packet is dropped -Else If router is using classless routing behavior then Router searches Level 1 supernet & default routes for a match If a match is found then Packet if forwarded -Else Packet is dropped Chapter 1 41

42 Summary Routing behaviors -This refers to how a routing table is searched Classful routing behavior -Indicated by the use of the no ip classless command -Router will not look beyond child routes for a lesser match Classless routing behavior -Indicated by the use of the ip classless command -Router will look beyond child routes for a lesser match Chapter 1 42

43 Chapter 1 43

44 EIGRP Routing Protocols and Concepts Chapter 9 Chapter 1 44

45 Objectives Describe the background and history of Enhanced Interior Gateway Routing Protocol (EIGRP). Examine the basic EIGRP configuration commands and identify their purposes. Calculate the composite metric used by EIGRP. Describe the concepts and operation of DUAL. Describe the uses of additional configuration commands in EIGRP. Chapter 1 45

46 Introduction ti Chapter 1 46

47 EIGRP Roots of EIGRP: IGRP -Developed in 1985 to overcome RIPv1 s limited hop count -Distance vector routing protocol -Metrics used by IGRP bandwidth b d (used by default) Delay (used by default) reliability load -Discontinued support starting with IOS 12.2(13)T & 12.2(R1s4)S Chapter 1 47

48 EIGRP EIGRP Message Format EIGRP Header Data link frame header - contains source and destination MAC address IP packet header - contains source & destination IP address EIGRP packet header - contains AS number Type/Length/Field - data portion of EIGRP message Chapter 1 48

49 EIGRP EIGRP packet header contains Opcode field Autonomous System number EIGRP Parameters contains Weights Hold time Chapter 1 49

50 EIGRP TLV: IP internal contains Metric field Subnet mask field Destination field TLV: IP external contains Fields used when external routes are imported into EIGRP routing process Chapter 1 50

51 EIGRP Protocol Dependent Modules (PDM) EIGRP uses PDM to route several different protocols i.e. IP, IPX & AppleTalk PDMs are responsible for the specific routing task for each network layer protocol Chapter 1 51

52 EIGRP Reliable Transport Protocol (RTP) Purpose of RTP Used by EIGRP to transmit and receive EIGRP packets Characteristics of RTP Involves both reliable & unreliable delivery of EIGRP packet Reliable delivery requires acknowledgment from destination Unreliable U delivery does not require an acknowledgement from destination Packets can be sent Unicast Multicast Using address Chapter 1 52

53 EIGRP EIGRP s 5 Packet Types Hello packets Used to discover & form adjacencies with neighbors Chapter 1 53

54 EIGRP Update packets Used to propagate routing information Acknowledgement packets Used to acknowledge receipt of update, query & reply packets Chapter 1 54

55 EIGRP Query & Reply packets Used by DUAL for searching for networks Query packets -Can use Unicast Multicast Reply pypacket -Use only unicast Chapter 1 55

56 EIGRP Purpose of Hello Protocol To discover & establish adjacencies with neighbor routers Characteristics of hello protocol Time interval for sending hello packet Most networks it is every 5 seconds Multipoint non broadcast multi-access networks Unicast every 60 seconds -Holdtime This is the maximum time router should wait before declaring a neighbor down Default holdtime 3 times hello interval Chapter 1 56

57 EIGRP EIGRP Bounded Updates EIGRP only sends update when there is a change in route status Partial update A partial update includes only the route information that t has changed the whole routing table is NOT sent Bounded update When a route changes, only those devices that are impacted will be notified of the change EIGRP s use of partial bounded updates minimizes use of bandwidth Chapter 1 57

58 EIGRP Diffusing Update Algorithm (DUAL) Purpose EIGRP s primary method for preventing routing loops Advantage of using DUAL Provides for fast convergence time by keeping a list of loop- free backup routes Chapter 1 58

59 EIGRP Administrative Distance (AD) Defined as the trustworthiness of the source route EIGRP default administrative distances Summary routes = 5 Internal routes = 90 Imported routes = 170 Chapter 1 59

60 EIGRP Authentication EIGRP can Encrypt routing information Authenticate routing information Chapter 1 60

61 EIGRP Network Topology Topology used is the same as previous chapters with the addition of an ISP router Chapter 1 61

62 EIGRP EIGRP will automatically summarize routes at classful boundaries Chapter 1 62

63 Basic EIGRP Configuration Autonomous System (AS) & Process IDs This is a collection of networks under the control of a single authority y( (reference RFC 1930) AS Numbers are assigned by IANA Entities needing AS numbers ISP Internet Backbone prodiers Institutions connecting to other institutions using AS numbers Chapter 1 63

64 Basic EIGRP Configuration EIGRP autonomous system number actually functions as a process ID Process ID represents an instance of the routing protocol running on a router Example Router(config)#router eigrp autonomous-system Chapter 1 64

65 Basic EIGRP Configuration The router eigrp command The global command that enables eigrp is router eigrp autonomous-system -All routers in the EIGRP routing domain must use the same process ID number (autonomous-system number) Chapter 1 65

66 Basic EIGRP Configuration The Network Command Functions of the network command Enables interfaces to transmit & receive EIGRP updates Includes network or subnet in EIGRP updates Example Router(config-router)#network network-address Chapter 1 66

67 Basic EIGRP Configuration The network Command with a Wildcard Mask -This option is used when you want to configure EIGRP to advertise specific subnets -Example Router(config-router)#network network-address [wildcard-mask] Chapter 1 67

68 Basic EIGRP Configuration Verifying EIGRP EIGRP routers must establish adjacencies with their neighbors before any updates can be sent or received Command used to view neighbor table and verify that EIGRP has established adjacencies with neighbors is show ip eigrp neighbors Chapter 1 68

69 EIGRP The show ip protocols command is also used to verify that EIGRP is enabled Chapter 1 69

70 Basic EIGRP Configuration Examining the Routing Table The show ip route command is also used to verify EIGRP EIGRP routes are denoted in a routing table by the letter D By default, EIGRP automatically summarizes routes at major network boundary Chapter 1 70

71 Basic EIGRP Configuration Introducing the Null0 Summary Route Null0 is not a physical interface In the routing table summary routes are sourced from Null0 Reason: routes are used for advertisement purposes EIGRP will automatically include a null0 summary route as child route when 2 conditions are met At least one subnet is learned via EIGRP Automatic summarization is enabled Chapter 1 71

72 Basic EIGRP Configuration R3 s routing table shows that the /1616 0/16 network is automatically summarized by R1 &R3 Chapter 1 72

73 EIGRP Metric Calculation l EIGRP Composite Metric & the K Values EIGRP uses the following values in its composite metric -Bandwidth, delay, reliability, and load The composite metric used by EIGRP formula used has values K1 K5 K1 & K3 = 1 all other K values = 0 Chapter 1 73

74 EIGRP Metric Calculation Use the sh ip protocols command to verify the K values Chapter 1 74

75 EIGRP Metric Calculation l EIGRP Metrics Use the show interfaces command dto view metrics EIGRP Metrics Bandwidth EIGRP uses a static bandwidth to calculate metric Most serial interfaces use a default bandwidth value of 1.544Mbos (T1) Chapter 1 75

76 EIGRP Metric Calculation EIGRP Metrics Delay is the defined as the measure of time it takes for a packet to traverse a route -it is a static value based on link type to which interface is connected Chapter 1 76

77 EIGRP Metric Calculation Reliability (not a default EIGRP metric) -A measure of the likelihood that a link will fail -Measure dynamically & expressed as a fraction of 255 the higher the fraction the better the reliability Load (not a default EIGRP metric) A number that reflects how much traffic is using a link Number is determined dynamically and is expressed as a fraction of 255 The lower the fraction the less the load on the link Chapter 1 77

78 EIGRP Metric Calculation l Using the Bandwidth Command Modifying the interface bandwidth -Use the bandwidth command -Example Router(config-if)#bandwidth kilobits Verifying bandwidth Use the show interface command Note bandwidth command does not change the link s physical bandwidth Use the interface command no bandwidth to restore the default value. Chapter 1 78

79 EIGRP Metric Calculation The EIGRP metric can be determined by examining the bandwidth delay Chapter 1 79

80 EIGRP Metric Calculation EIGRP uses the lowest bandwidth (BW)in its metric calculation l Calculated BW = reference BW / lowest BW(kbps) Delay EIGRP uses the cumulative sum of all outgoing interfaces Calculated Delay = the sum of outgoing interface delays EIGRP Metric = calculated BW + calculated delay Chapter 1 80

81 EIGRP Metric Calculation Chapter 1 81

82 DUAL Concepts The Diffusing Update Algorithm (DUAL) is used to prevent looping Successor Feasible Distance (FD) Feasible Successor (FS) Reported Distance (RD) or Advertised Distance (AD) Feasible Condition or Feasibility Condition (FC) Chapter 1 82

83 DUAL Concepts Successor The best least cost route to a destination found in the routing table Feasible distance The lowest calculated metric along a path to a destination network Chapter 1 83

84 DUAL Concepts Feasible Successors, Feasibility Condition & Reported Distance Feasible Successor -This is a loop free backup route to same destination as successor route Chapter 1 84

85 DUAL Concepts Feasible Successors, Feasibility Condition & Reported Distance Reported distance (RD) -The metric that a router reports to a neighbor about its own cost to that network Chapter 1 85

86 DUAL Concepts Feasibility Condition (FC) -Met when a neighbor s RD is less than the local l router s FD to the same destination network Chapter 1 86

87 DUAL Concepts Topology Table: Successor & Feasible Successor EIGRP Topology table Viewed using the show ip eigrp topology command Contents of table include: all successor routes all feasible successor routes Chapter 1 87

88 DUAL Concepts EIGRP Topology Table dissected Chapter 1 88

89 DUAL Concepts Topology Table: No Feasible Successor Af feasible successor may not be present because the feasibility condition may not be met -In other words, the reported distance of the neighbor is greater than or equal to the current feasible distance Chapter 1 89

90 DUAL Concepts Finite State Machine (FSM) An abstract machine that defines a set of possible states something can go through, what event causes those states and what events ents result form those states FSMs are used to describe how a device, computer program, or routing algorithm will react to a set of input events Chapter 1 90

91 DUAL Concepts DUAL FSM Selects a best loopfree path to a destination Selects alternate routes by using information in EIGRP tables Chapter 1 91

92 DUAL Concepts Finite State Machines (FSM) To examine e output from EIGRP s finite state machine us the debug eigrp fsm command Chapter 1 92

93 More EIGRP Configurations The Null0 Summary Route By default, EIGRP uses the Null0 interface to discard any packets that match the parent route but do not match any of the child routes EIGRP automatically includes a null0 summary route as a child route whenever both of the following conditions exist One or subnets exists that was learned via EIGRP Automatic summarization is enabled Chapter 1 93

94 More EIGRP Configurations The Null0 Summary Route Chapter 1 94

95 More EIGRP Configurations Disabling Automatic Summarization The auto-summary command permits EIGRP to automatically summarize at major network boundaries The no auto-summary command is used to disable automatic summarization This causes all EIGRP neighbors to send updates that will not be automatically summarized this will cause changes to appear in both -routing tables -topology tables Chapter 1 95

96 More EIGRP Configurations Manual Summarization Manual summarization can include supernets Reason: EIGRP is a classless routing protocol & include subnet mask in update Command used to configure manual al summarization ation Router(config-if)#ip summary-address eigrp as-number network-address subnet-mask Chapter 1 96

97 More EIGRP Configurations i Configuring a summary route in EIGRP Chapter 1 97

98 More EIGRP Configurations EIGRP Default Routes quad zero static default route -Can be used with any currently supported routing protocol -Is usually configured on a router that is connected a network outside the EIGRP domain EIGRP & the Quad zero static default route Requires the use of the redistribute static command to disseminate default route in EIGRP updates Chapter 1 98

99 More EIGRP Configurations Fine-Tuning EIGRP EIGRP bandwidth utilization -By default, EIGRP uses only up to 50% of interface bandwidth for EIGRP information -The command to change the percentage of bandwidth used by EIGRP is Router(config-if)#ip bandwidth-percent eigrp asnumber percent Chapter 1 99

100 More EIGRP Configurations Configuring g Hello Intervals and Hold Times -Hello intervals and hold times are configurable on a per-interface basis -The command to configure hello interval is Router(config-if)#ip hello-interval eigrp as-number seconds Changing the hello interval also requires changing the hold time to a value greater than or equal to the hello interval -The command to configure hold time value is Router(config-if)#ip hold-time eigrp as-number seconds Chapter 1 100

101 Summary Background & History EIGRP is a derivative of IGRP EIGRP is a Cisco proprietary distance vector routing protocol released in 1994 EIGRP terms and characteristics EIGPR uses RTP to transmit & receive EIGRP packets EIGRP has 5 packet type: Hello packets Update packets Acknowledgement packets Query packets Reply packets Supports VLSM & CIDR Chapter 1 101

102 Summary EIGRP terms and characteristics EIGRP uses a hello protocol Purpose of hello protocol is to discover & establish adjacencies EIGRP routing updates Aperiodic Partial P l and bounded d Fast convergence Chapter 1 102

103 Summary EIGRP commands The following commands are used for EIGRP configuration RtrA(config)#router eigrp [autonomous-system #] RtrA(config-router)#network network-number The following commands can be used to verify EIGRP Show ip protocols Show ip eigrp neighbors Show ip route Chapter 1 103

104 Summary EIGRP metrics include Bandwidth (default) Delay (default) Reliability Load Chapter 1 104

105 Summary DUAL Purpose of DUAL To prevent routing loops Successor Primary Pi route to a destination Feasible successor Backup route to a destination Feasible distance Lowest calculated metric to a destination Reported distance The distance towards a destination as advertised by an upstream neighbor Chapter 1 105

106 Summary Choosing the best route After router has received all updates from directly connected neighbors, it can calculate its DUAL 1 st metric is calculated for each route 22 nd route with lowest metric is designated successor & is placed in routing table 3 rd feasible successor is found Criteria for feasible successor: it must have lower reported distance to the destination than the installed route s feasible distance Feasible routes are maintained in topology table Chapter 1 106

107 Summary Automatic summarization On by default Summarizes routes on classful boundary Summarization can be disabled using the following command RtrA(config-if)#no auto-summary Chapter 1 107

108 Chapter 1 108