2008 NDP Lectures 7 th Semester

Transcription

1 2008 NDP Lectures 7 th Semester Neeli R. Prasad, Associate Professor Head of Wireless Security and Sensor Networks Group Networking and Security Aalborg University Niels Jernes Vej 12, 9220 Aalborg East, Denmark np@es.aau.dk Tel.:

2 October 20, 2008 NDP Lectures 7 th Semester 12:30 13:15 Guest lecture from Telia Sonera 13:15 13:25 Break 13:25 14:10 IP Routing 14:10 14:25 Break 14:25 16:00 Students assignments

3 Routing Overview Outline

4 Determining IP Routes

5 Objectives Upon completing this lecture, you will be able to: Describe the features and operation of static routing Describe the features and operation of dynamic routing protocols, including RIP, IGRP, EIGRP, and OSPF Build a functional router configuration to support the specified network operational requirements, given a network design Use show commands to identify anomalies in routing operation, given an operational router Use debug commands to identify events and anomalies in routing operation, given an operational router

6 Routing Overview 6

7 Objectives Upon completing this lesson, you will be able to: Explain the differences between static routing and dynamic routing Identify the classes of routing protocols Use Cisco IOS commands to configure static routes and default route forwarding, given a functioning router Use show commands to identify anomalies in static routing operation, given an operational router Describe the operation of router on a stick Configure router on a stick for inter-vlan routing using ISL and 802.1Q trunking, given an operational switch and router

8 What Is Routing? To route, a router needs to do the following: Know the destination address Identify the sources it can learn from Discover possible routes Select the best route Maintain and verify routing information

9 What Is Routing? (Cont.) Routers must learn destinations that are not directly connected.

10 Identifying Static and Dynamic Routes Static Route Uses a route that a network administrator enters into the router manually Dynamic Route Uses a route that a network routing protocol adjusts automatically for topology or traffic changes

11 Static Routes Configure unidirectional static routes to and from a stub network to allow communications to occur.

12 Static Route Configuration Router(config)#ip route network [mask] {address interface}[distance] [permanent] Defines a path to an IP destination network or subnet or host

13 Static Route Example This is a unidirectional route. You must have a route configured in the opposite direction.

14 Default Routes This route allows the stub network to reach all known networks beyond router A.

15 Verifying the Static Route Configuration router#show ip route 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-IS level-1, L2 - IS-IS level-2, * - candidate default U - per-user static route Gateway of last resort is to network /8 is subnetted, 1 subnets C is directly connected, Serial0 S* /0 is directly connected, Serial0

16 What Is a Routing Protocol? Routing protocols are used between routers to determine paths and maintain routing tables. Once the path is determined, a router can route a routed protocol.

17 Autonomous Systems: Interior or Exterior Routing Protocols An autonomous system is a collection of networks under a common administrative domain. IGPs operate within an autonomous system. EGPs connect different autonomous systems.

18 Administrative Distance: Ranking Routes

19 Classes of Routing Protocols

20 Classful Routing Overview Classful routing protocols do not include the subnet mask with the route advertisement. Within the same network, consistency of the subnet masks is assumed. Summary routes are exchanged between foreign networks. Examples of classful routing protocols: RIP Version 1 (RIPv1) IGRP

21 Classless Routing Overview Classless routing protocols include the subnet mask with the route advertisement. Classless routing protocols support variablelength subnet masking (VLSM). Summary routes can be manually controlled within the network. Examples of classless routing protocols: RIP Version 2 (RIPv2) EIGRP OSPF IS-IS

22 Routing Protocol Comparison Chart

23 Using the ip classless Command

24 VLAN-to-VLAN Overview Network layer devices combine multiple broadcast domains.

25 Dividing a Physical Interface into Subinterfaces Physical interfaces can be divided into multiple subinterfaces.

26 Routing Between VLANs with ISL Trunks

27 Routing Between VLANs with 802.1Q Trunks

28 Distance Vector Routing 28

29 Objectives Upon completing this lesson, you will be able to: Describe the features offered by distance vector routing protocols and give examples of each Describe the issues associated with distance vector routing and identify solutions to those issues

30 Distance Vector Routing Protocols Routers pass periodic copies of routing table to neighbor routers and accumulate distance vectors.

31 Sources of Information and Discovering Routes Routers discover the best path to destinations from each neighbor.

32 Selecting the Best Route with Metrics

33 Maintaining Routing Information Updates proceed step-by-step from router to router.

34 Inconsistent Routing Entries Each node maintains the distance from itself to each possible destination network.

35 Inconsistent Routing Entries (Cont.) Slow convergence produces inconsistent routing.

36 Inconsistent Routing Entries (Cont.) Router C concludes that the best path to network is through router B.

37 Inconsistent Routing Entries (Cont.) Router A updates its table to reflect the new but erroneous hop count.

38 Count to Infinity Hop count for network counts to infinity.

39 Defining a Maximum Define a limit on the number of hops to prevent infinite loops.

40 Routing Loops Packets for network bounce (loop) between routers B and C.

41 Split Horizon It is never useful to send information about a route back in the direction from which the original information came.

42 Route Poisoning Routers advertise the distance of routes that have gone down to infinity.

43 Poison Reverse Poison reverse overrides split horizon.

44 Holddown Timers The router keeps an entry for the network s possible down state, allowing time for other routers to recompute for this topology change.

45 Triggered Updates The router sends updates when a change in its routing table occurs.

46 Distance Vector Operation

47 Distance Vector Operation (Cont.)

48 Distance Vector Operation (Cont.)

49 Distance Vector Operation (Cont.)

50 Distance Vector Operation (Cont.)

51 Distance Vector Operation (Cont.)

52 Summary Distance vector-based routing algorithms (also known as Bellman-Ford algorithms) pass periodic copies of a routing table from router to router. When the topology in a distance vector protocol internetwork changes, routing table updates must occur. As with the network discovery process, topology change updates proceed step-by-step from router to router. When maintaining the routing information, inconsistencies can occur if the internetwork s slow convergence on a new configuration causes incorrect routing entries.

53 Summary (Cont.) The condition called count to infinity arises when routing table updates continue to increase the metric to a destination that cannot be reached, rather than marking the destination as unreachable. A routing loop occurs when two or more routers have incorrect routing information indicating that a valid path to an unreachable destination exists through the other routers. A number of techniques are available to eliminate routing loops including: split horizon, route poisoning, poison reverse, holddown timers, and triggered updates.

54 Link-State and Balanced Hybrid Routing 54

55 Objectives Upon completing this lesson, you will be able to: Describe the issues associated with link-state routing and identify solutions to those issues Describe the features of balanced hybrid routing protocols

56 Link-State Routing Protocols After initial flood, pass small event-triggered link-state updates to all other routers

57 Link-State Network Hierarchy Example Minimizes routing table entries Localizes impact of a topology change within an area

58 Link-State Routing Protocol Algorithms

59 Benefits of Link-State Routing Fast convergence: changes are reported immediately by the source affected. Robustness against routing loops: Routers know the topology. Link-state packets are sequenced and acknowledged. By careful (hierarchical) network design, you can utilize resources optimally.

60 Caveats of Link-State Routing Significant demands for resources: Memory (three tables: adjacency, topology, forwarding) CPU (Dijkstra s algorithm can be intensive, especially when a lot of instabilities are present.) Requires very strict network design (when more areas area routing) Problems with partitioning of areas Configuration generally simple but can be complex when tuning various parameters and when the design is complex Troubleshooting easier than in distance vector routing

61 Drawbacks to Link-State Routing Protocols Initial discovery may cause flooding. Memory- and processor-intensive.

62 Balanced Hybrid Routing Shares attributes of both distance vector and link-state routing

63 Summary Link-state routing uses LSAs, a topological database, the SPF algorithm, the resulting SPF tree, and a routing table of paths and ports to each network. Link-state routing algorithms maintain a complex database of the network's topology by exchanging LSAs with other routers in a network. Link-state routing may flood the network with LSAs during initial topology discovery and can be both memory- and processor-intensive. Balanced hybrid routing protocols combine aspects of both distance vector and link-state protocols.

64 Enabling RIP 64

65 Objectives Upon completing this lesson, you will be able to: Describe the features and operation of RIP Use Cisco IOS commands to configure dynamic routing using RIP, given a functioning router Use show and debug commands to identify anomalies in dynamic routing operation using RIP, given an operational router

66 RIP Overview Maximum is 6 paths (default = 4) Hop-count metric selects the path Routes update every 30 seconds

67 IP Routing Configuration Tasks Router configuration Select routing protocols. Specify networks or interfaces.

68 Dynamic Routing Configuration Router(config)#router protocol [keyword] Defines an IP routing protocol Router(config-router)#network network-number Mandatory configuration command for each IP routing process Identifies the physically connected network that routing updates are forwarded to

69 RIP Configuration Router(config)#router rip Starts the RIP routing process Router(config-router)#network network-number Selects participating attached networks Requires a major classful network number

70 RIP Configuration Example

71 Verifying the RIP Configuration

72 Displaying the IP Routing Table

73 debug ip rip Command

74 Summary RIP is a distance vector routing protocol that uses hop count as the metric for route selection and broadcasts routing updates every 30 seconds. To enable a dynamic routing protocol, you will select the routing protocol and then assign IP network numbers. The router rip command specifies RIP as the routing protocol. The network command identifies a participating attached network. The show ip commands display information about routing protocols and the routing table. Use the debug ip rip command to display information on RIP routing transactions.

75 Enabling IGRP 75

76 Objectives Upon completing this lesson, you will be able to: Describe the features and operation of IGRP Use Cisco IOS commands to configure dynamic routing using IGRP, given a functioning router Use show and debug commands to identify anomalies in dynamic routing operation using IGRP, given an operational router

77 Introducing IGRP More scalable than RIP Sophisticated metric Multiple-path support

78 IGRP Composite Metric Bandwidth Delay Reliability Loading MTU

79 IGRP Unequal Multiple Paths Maximum 6 paths (default = 4) Within metric variance Next-hop router closer to destination

80 Configuring IGRP Router(config)#router igrp autonomous-system Defines IGRP as the IP routing protocol Router(config-router)#network network-number Selects participating attached networks

81 Configuring IGRP (cont.) Router(config-router)#variance multiplier Controls IGRP load balancing Router(config-router)#traffic-share {balanced min} Controls how load-balanced traffic is distributed

82 IGRP Configuration Example

83 Verifying the IGRP Configuration

84 Displaying the IP Routing Table

85 debug ip igrp transaction Command

86 debug ip igrp events Command RouterA#debug ip igrp events IGRP event debugging is on RouterA# 00:23:44: IGRP: sending update to via Ethernet0 ( ) 00:23:44: IGRP: Update contains 0 interior, 2 system, and 0 exterior routes. 00:23:44: IGRP: Total routes in update: 2 00:23:44: IGRP: sending update to via Serial2 ( ) 00:23:45: IGRP: Update contains 0 interior, 1 system, and 0 exterior routes. 00:23:45: IGRP: Total routes in update: 1 00:23:48: IGRP: received update from on Serial2 00:23:48: IGRP: Update contains 1 interior, 1 system, and 0 exterior routes. 00:23:48: IGRP: Total routes in update: 2

87 Updating Routing Information Example

88 Updating Routing Information Example (Cont.)

89 Updating Routing Information Example (Cont.)

90 Updating Routing Information Example (Cont.)

91 Summary IGRP has several key features such as increased scalability, a sophisticated metric, and multiple paths. IGRP uses a composite routing metric that can include bandwidth, delay, reliability, loading, and MTU value. The IGRP composite routing metric supports multiple paths between source and destination. Use the router igrp and network commands to create an IGRP routing process. Use the variance and traffic-share commands to configure IGRP load balancing. Use the show ip protocols and show ip route commands to display information about your IGRP configuration. Use the debug ip igrp transaction command to display transaction information on IGRP routing transactions and the debug ip igrp events command to display a summary of the IGRP routing information.

92 Enabling EIGRP 92

93 Objectives Upon completing this lesson, you will be able to: Describe the features and operation of EIGRP Use Cisco IOS commands to configure dynamic routing using EIGRP, given a functioning router Use show and debug commands to identify anomalies in dynamic routing operation using EIGRP, given an operational router

94 Introducing EIGRP EIGRP supports: Rapid convergence Reduced bandwidth usage Multiple network-layer protocols

95 EIGRP Terminology

96 Comparing EIGRP and IGRP Similar metric Same load balancing Improved convergence time Reduced network overhead

97 Configuring EIGRP Router(config)#router eigrp autonomous-system Defines EIGRP as the IP routing protocol Router(config-router)#network network-number Selects participating attached networks

98 EIGRP Configuration Example

99 Verifying the EIGRP Router#show ip route eigrp Router#show ip protocols Configuration Router#show ip eigrp neighbors Displays the neighbors discovered by IP EIGRP Router#show ip eigrp topology Displays the IP EIGRP topology table Displays current EIGRP entries in the routing table Displays the parameters and current state of the active routing protocol process Router#show ip eigrp traffic Displays the number of IP EIGRP packets sent and received

100 debug ip eigrp Command Router#debug ip eigrp IP-EIGRP: Processing incoming UPDATE packet IP-EIGRP: Ext M SM IP-EIGRP: Ext M SM IP-EIGRP: Ext M SM IP-EIGRP: , - do advertise out Ethernet0/1 IP-EIGRP: Ext metric IP-EIGRP: , - do advertise out Ethernet0/1 IP-EIGRP: Ext metric IP-EIGRP: , - do advertise out Ethernet0/1 IP-EIGRP: Ext metric IP-EIGRP: , - do advertise out Ethernet0/1 IP-EIGRP: Ext metric IP-EIGRP: , - do advertise out Ethernet0/1

101 Summary EIGRP is an interior gateway protocol suited for many different topologies and media. EIGRP is an enhanced version of the IGRP developed by Cisco, with improved convergence properties and operating efficiency over IGRP. Use the router eigrp and network commands to create an EIGRP routing process. Use the show ip eigrp commands to display information about your EIGRP configuration. To display information on EIGRP packets, use the debug ip eigrp privileged EXEC command.

102 Enabling OSPF 102

103 Objectives Upon completing this lesson, you will be able to: Describe the features and operation of OSPF Use Cisco IOS commands to configure dynamic routing for a single area OSPF network, given a functioning router Use show and debug commands to identify anomalies in dynamic routing operation using OSPF, given an operational router

104 Introducing OSPF Open standard Shortest path first (SPF) algorithm Link-state routing protocol (vs. distance vector)

105 OSPF as a Link-State Protocol OSPF propagates link-state advertisements rather than routing table updates. LSAs are flooded to all OSPF routers in the area. The OSPF link-state database is pieced together from the LSAs generated by the OSPF routers. OSPF uses the SPF algorithm to calculate the shortest path to a destination. Link = router interface State = description of an interface and its relationship to neighboring routers

106 OSPF Hierarchical Routing Consists of areas and autonomous systems Minimizes routing update traffic

107 Shortest Path First Algorithm Places each router at the root of a tree and calculates the shortest path to each destination based on the cumulative cost Cost = 10 8 /bandwidth (bps)

108 Configuring Single Area OSPF Router(config)#router ospf process-id Defines OSPF as the IP routing protocol Router(config-router)#network address mask area area-id Assigns networks to a specific OSPF area

109 OSPF Configuration Example

110 Configuring Loopback Interfaces Router ID: Number by which the router is known to OSPF Default: The highest IP address on an active interface at the moment of OSPF process startup Can be overridden by a loopback interface: Highest IP address of any active loopback interface

111 Verifying the OSPF Configuration Router#show ip protocols Verifies that OSPF is configured Router#show ip route Displays all the routes learned by the router Router#show ip ospf interface Displays area-id and adjacency information Router#show ip ospf neighbor Displays OSPF-neighbor information on a per-interface basis

112 OSPF debug commands Router#debug ip ospf events OSPF:hello with invalid timers on interface Ethernet0 hello interval received 10 configured 10 net mask received configured dead interval received 40 configured 30 Router# debug ip ospf packet OSPF: rcv. v:2 t:1 l:48 rid: aid: chk:6ab2 aut:0 auk: Router#debug ip ospf packet OSPF: rcv. v:2 t:1 l:48 rid: aid: chk:0 aut:2 keyid:1 seq:0x0

113 Summary OSPF is an interior gateway protocol similar to IGRP, but based on link states rather than distance vectors. OSPF advertises information about each of its links rather than sending routing table updates like a distance vector protocol. The SPF algorithm places each router at the root of a tree and calculates the shortest path to each destination based on the cumulative cost required to reach that destination.

114 Summary (Cont.) Use the router ospf command to start an OSPF routing process and the network command to associate addresses to an OSPF area. You can use any one of a number of show commands to display information about an OSPF configuration. To display information on OSPF-related events, such as adjacencies, flooding information, designated router selection, and SPF calculation, use the debug ip ospf events privileged EXEC command.

115 Summary Routing is the process by which an item gets from one location to another. In networking, a router is the device used to route traffic. Routers can forward packets over static routes or dynamic routes, based on the router configuration. Static routes can be important if the Cisco IOS software cannot build a route to a particular destination. Static routes are also useful for specifying a gateway of last resort to which all unroutable packets will be sent. A default route is a special type of static route used for situations when the route from a source to a destination is not known or when it is unfeasible for the routing table to store sufficient information about the route.

116 Summary (Cont.) When the static routing configuration is complete, use the show ip route command to verify the configuration. Dynamic routing relies on a routing protocol to disseminate knowledge. A routing protocol defines the set of rules used by a router when it communicates with neighboring routers. The ip classless command prevents a router from dropping a packet destined for an unknown subnet. In a VLAN environment, frames are only switched between ports within the same broadcast domain so a Layer 3 device is required to enable inter-vlan communication. Use ISL or 802.1q to enable trunking on a router s subinterface.

117 Thank you!!