Lab 4: Routing using OSPF

Transcription

1 Network Topology:- Lab 4: Routing using OSPF Device Interface IP Address Subnet Mask Gateway/Clock Description Rate Fa 0/ R1 LAN R1 Se 0/0/ Link to R2 Se 0/0/ Link to R3 Fa 0/ R2 LAN R2 Se 0/0/ Link to R1 Se 0/0/ Link to R3 Fa 0/ R3 LAN R3 Se 0/0/ Link to R2 Se 0/0/ Link to R1 PC1 NIC PC2 NIC PC3 NIC Objective: This lab configures routers using Open Shortest Path First Protocol (OSPF) so that all devices can ping any other device. Upon Completion You will learn: 1. Configure OSPF routing on all routers. 2. Learn OSPF router IDs. 3. Loopback addressing. 4. Verify OSPF routing using show commands. Theory: 1

2 OSPF is an interior gateway protocol that routes Internet Protocol (IP) packets solely within a single routing domain (autonomous system). It gathers link state information from available routers and constructs a topology map of the network. The topology determines the routing table presented to the Internet Layer which makes routing decisions based solely on the destination IP address found in IP packets. OSPF was designed to support variable-length subnet masking (VLSM) or Classless Inter- Domain Routing (CIDR) addressing models. OSPF detects changes in the topology, such as link failures, very quickly and converges on a new loop-free routing structure within seconds. It computes the shortest path tree for each route using a method based on Dijkstra's algorithm, a shortest path first algorithm. The link-state information is maintained on each router as a link-state database (LSDB) which is a tree-image of the entire network topology. Identical copies of the LSDB are periodically updated through flooding on all OSPF routers. The OSPF routing policies to construct a route table are governed by link cost factors (external metrics) associated with each routing interface. Cost factors may be the distance of a router (roundtrip time), network throughput of a link, or link availability and reliability, expressed as simple unitless numbers. This provides a dynamic process of traffic load balancing between routes of equal cost. An OSPF network may be structured, or subdivided, into routing areas to simplify administration and optimize traffic and resource utilization. Areas are identified by 32-bit numbers, expressed either simply in decimal, or often in octet-based dot-decimal notation, familiar from IPv4 address notation. By convention, Area 0 (zero) or represents the core or backbone region of an OSPF network. The identifications of other areas may be chosen at will; often, administrators select the IP address of a main router in an area as the area's identification. Each additional area must have a direct or virtual connection to the backbone OSPF area. Such connections are maintained by an interconnecting router, known as Area Border Router (ABR). An ABR maintains separate link state databases for each area it serves and maintains summarized routes for all areas in the network. OSPF does not use a TCP/IP transport protocol (UDP, TCP), but is encapsulated directly in IP datagrams with protocol number 89. This is in contrast to other routing protocols, such as the Routing Information Protocol (RIP), or the Border Gateway Protocol (BGP). OSPF handles its own error detection and correction functions. Routers in the same broadcast domain or at each end of a point-to-point telecommunications link form adjacencies when they have detected each other. This detection occurs when a router identifies itself in a hello OSPF protocol packet. This is called a two-way state and is the most basic relationship. The routers in an Ethernet or frame relay network select a designated router (DR) and a backup designated router (BDR) which act as a hub to reduce traffic between routers. OSPF uses both unicast and multicast to send "hello packets" and link state updates. As a link state routing protocol, OSPF establishes and maintains neighbor relationships in order to exchange routing updates with other routers. The neighbor relationship table is called an adjacency database in OSPF. Provided that OSPF is configured correctly, OSPF forms neighbor relationships only with the routers directly connected to it. In order to form a neighbor relationship between two routers, the interfaces used to form the relationship must be in the same area. An interface can only belong to a single area. Router Identities: Each router in an OSPF network needs a unique ID that is used to provide a unique identity to the OSPF router. The router ID is chosen according to one of the two following criteria: 2

3 The highest IP address on its loop back interfaces (this is a logical interface on a router(. The highest IP address on its active interfaces. OSPF learns about its neighbors and builds its adjacency and topology tables by sharing LSAs OSPF routers will generate hello LSAs every 10 seconds. If a neighbor is not seen within the dead interval time, which defaults to 40 seconds, the neighbor is declared dead. First before a router will accept any routing information from another OSPF router, they have to build an adjacency with each other on their connected interfaces. When this adjacency is built, the two routers (on the connected interfaces) are called a neighbor, which indicates a special relationship between the two. In order for two routers to become neighbors, the following must match on each router: The area number and its type. The hello and dead interval timers. The OSPF password (optional), if it is configured. The area stub flag (used to contain OSPF messages and routing information). Thus, OSPF routers will go through three states called the exchange process: 1. Down state: The new router has not exchanged any OSPF information with any other router. 2. Init state: A destination router has received a new router's hello and adds it to its neighbor list (assuming that certain values match). Note that communication is only unidirectional at this point. 3. Two-Way state: The new router receives a unidirectional reply to its initial hello packet and adds destination router to its neighbor database. Once the routers have entered a two-way state, they are considered neighbors. For each network multi-access segment, there is a DR and a BDR as well as other routers. This process is true for multi-access segments, (an example, if you have ten VLANs in your switched area, you ll have ten DRs and ten BDRs.) but not point-to-point links, where DRs are not necessary. The router with the highest priority (or highest router ID) becomes the DR. Loop back Interfaces: A loop back interface is a logical, virtual interface on a router that always remains up. By default, the router doesn't have any loop back interfaces, but they can easily be created. OSPF routers use Link State Advertisements (LSAs) to communicate with each other. One type of LSA is a hello, which is used to form neighbor relationships and as a keep-alive function. Hellos are generated every ten seconds. Area types: An OSPF domain is divided into areas that are labeled with 32-bit area identifiers. The area identifiers are commonly, but not always, written in the dot-decimal notation of an IPv4 address. However, they are not IP addresses and may duplicate, without conflict, any IPv4 address. Areas are logical groupings of hosts and networks, including their routers having interfaces connected to any of the included networks. Each area maintains a separate link state database whose information may be summarized towards the rest of the network by the connecting router. Thus, the topology of an area is unknown outside of the area. This reduces the amount of routing traffic between parts of an autonomous system. (An ABR simulation shows how an ABR lets areas know each other's network addresses by flooding Summary LSA). Several special area types are defined:- 1. Backbone area: The backbone area (also known as area 0 or area ) forms the core of an OSPF network. All other areas are connected to it, and inter-area routing happens via 3

4 routers connected to the backbone area and to their own associated areas. It is the logical and physical structure for the "OSPF domain" and is attached to all nonzero areas in the OSPF domain. The backbone area is responsible for distributing routing information between nonbackbone areas. The backbone must be contiguous, but it does not need to be physically contiguous; backbone connectivity can be established and maintained through the configuration of virtual links. 2. Stub area: A stub area is an area which does not receive route advertisements external to the autonomous system (AS) and routing from within the area is based entirely on a default route. Sharing Routing Information After electing the DR/BDR pair, the routers continue to generate hellos to maintain communication. This is considered an EXStart state, in which the OSPF routers are ready to share link state information. The process the routers go through is called an exchange protocol 1. EXStart state: The DR and BDR form adjacencies with the other OSPF routers on the segment, and then within each adjacency, the router with the highest router ID becomes the master and starts the exchange process first (shares its link state information) note that the DR is not necessarily the master for the exchange process. The remaining router in the adjacency will be the slave. 2. Exchange state: The master starts sharing link state information first, with the slave. These are called DBDs (database description packets), also referred to as DDPs. The DBDs contain the link-state type, the ID of the advertising router, the cost of the advertised link, and the sequence number of the link. The slave responds back with an LSACK an acknowledgment to the DBD from the master. The slave then compares the DBD's information with its own. 3. Loading state: If the master has more up-to-date information than the slave, the slave will respond to the master's original DBD with an LSR (Link State Request). The master will then send a LSU (Link State Update) with the detailed information of the links to the slave. The slave will then incorporate this into its local link state database. Again, the slave will generate an LSACK to the master to acknowledge the fact that it received the LSU. If a slave has more up-to-date information, it will repeat the "exchange" and "loading" states. 4. Full state: Once the master and the slave are synchronized, they are considered to be in a full state. To summarize these four steps, OSPF routers share a type of LSA message in order to disclose information about available routes. Basically, an LSA update message contains a link and a state, as well as other information. Cost metric is the inverse of the accumulated bandwidth values of routers interfaces. The default measurement that Cisco uses in calculating the cost metric is: cost = the inverse of interface bandwidth. Scenario: You have built a lab network that had the configurations above. After which you have to configure the routers and the PCs with IP addresses, then configure the routers to actually route the packets between the networks. In this lab practice, you will use OSPF routing protocol to construct the routing tables. So you have to configure the routers with OSPF and define the networks and areas, so that all devices can ping any other device. 4

5 Practice1:- Now you are ready to use Packet Tracer to build your network and apply your lab network routing schemes. Task 1: Configure The Interfaces and PCs Step 1. Configure the routers' interfaces and the PCs to have the IP addresses in the table above. Step 2. Save the running configurations into NVRam. Task 2: Configure The OSPF Routing on R1, R2 & R3 Step 1. Turn on the OSPF routing on R1 using router ospf 1 command in the configuration mode. R1(config)#router ospf 1 R1(config-router)# Step 2. Add the networks connected to the router to be used in the update process. The command goes as follows: network <network_address> <number_of_ips> area <area_id> R1(config-router)#network area 0 R1(config-router)#network area 0 R1(config-router)#network area 0 R1(config-router)#exit R1(config)# Step 3. Repeat those steps on R2. R2(config)#router ospf 1 R2(config-router)#network area 0 R2(config-router)#network area 0 R2(config-router)#network area 0 R2(config-router)#exit R2(config)# Step 4. Repeat those steps on R3. R3(config)#router ospf 1 R3(config-router)#network area 0 R3(config-router)#network area 0 R3(config-router)#network area 0 R3(config-router)#exit R3(config)# Task 3: Verify OSPF Operation Step 2 Use the show ip protocol command to view information about the routing protocol The show ip protocols command displays the routing protocol that is currently configured on the router. This output can be used to verify most RIP parameters to confirm that:- RIP routing is configured. The correct interfaces send and receive RIP updates. The router advertises the correct networks. RIP neighbors are sending updates. Step 1. Use the show ip ospf neighbor command to information about other routers are learned. R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface FULL/ - 00:00: Serial0/0/ FULL/ - 00:00: Serial0/0/1 5

6 Step 2. Use the show ip protocol command to view information about the routing protocol. Routing Protocol is "ospf 1" Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Router ID Number of areas in this router is 1. 1 normal 0 stub 0 nssa Maximum path: 4 Routing for Networks: area area area 0 Routing Information Sources: Gateway Distance Last Update :03: :03:10 Distance: (default is 110) Step 3. Try also the following command: show ip route, show ip ospf interface, and show ip ospf. R1#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 N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 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, ia - IS-IS inter area - * candidate default, U - per-user static route, o - ODR P - periodic downloaded static route Gateway of last resort is not set 42/ is subnetted, 1 subnets O [110/65] via , 00:11:40, Serial0/0/0 42/ is subnetted, 2 subnets C is directly connected, FastEthernet0/0 O [110/65] via , 00:05:31, Serial0/0/1 01/ is subnetted, 3 subnets C is directly connected, Serial0/0/0 C is directly connected, Serial0/0/1 O [110/128] via , 00:11:24, Serial0/0/0 [110/128] via , 00:05:31, Serial0/0/1 O Identifies the source of the route as OSPF Indicates the address of the remote network. [110/65] Indicates the administrative distance (110) and the cost (65). via Specifies the address of the next-hop router (R2) to send traffic to for the remote network. Serial0/0/0 Specifies the local interface through which the remote network can be reached. R1#show ip ospf interface FastEthernet0/0 is up, line protocol is up Internet address is /28, Area 0 Process ID 1, Router ID , Network Type BROADCAST, Cost: 1 Transmit Delay is 1 sec, State DR, Priority 1 Designated Router (ID) , Interface address No backup designated router on this network Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 Hello due in 00:00:09 Index 1/1, flood queue length 0 Next 0x0(0)/0x0(0) Last flood scan length is 1, maximum is 1 Last flood scan time is 0 msec, maximum is 0 msec Neighbor Count is 0, Adjacent neighbor count is 0 Suppress hello for 0 neighbor(s) 6

7 Serial0/0/0 is up, line protocol is up Internet address is /30, Area 0 Process ID 1, Router ID , Network Type POINT-TO-POINT, Cost: 64 Transmit Delay is 1 sec, State POINT-TO-POINT, Priority 0 No designated router on this network No backup designated router on this network Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 Hello due in 00:00:03 Index 2/2, flood queue length 0 Next 0x0(0)/0x0(0) Last flood scan length is 1, maximum is 1 Last flood scan time is 0 msec, maximum is 0 msec Neighbor Count is 1, Adjacent neighbor count is 1 Adjacent with neighbor Suppress hello for 0 neighbor(s) Serial0/0/1 is up, line protocol is up Internet address is /30, Area 0 Process ID 1, Router ID , Network Type POINT-TO-POINT, Cost: 64 Transmit Delay is 1 sec, State POINT-TO-POINT, Priority 0 No designated router on this network No backup designated router on this network Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 Hello due in 00:00:02 Index 3/3, flood queue length 0 Next 0x0(0)/0x0(0) Last flood scan length is 1, maximum is 1 Last flood scan time is 0 msec, maximum is 0 msec Neighbor Count is 1, Adjacent neighbor count is 1 Adjacent with neighbor Suppress hello for 0 neighbor(s) R1#show ip ospf Routing Process "ospf 1" with ID Supports only single TOS(TOS0) routes Supports opaque LSA SPF schedule delay 5 secs, Hold time between two SPFs 10 secs Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs Number of external LSA 0. Checksum Sum 0x Number of opaque AS LSA 0. Checksum Sum 0x Number of DCbitless external and opaque AS LSA 0 Number of DoNotAge external and opaque AS LSA 0 Number of areas in this router is 1. 1 normal 0 stub 0 nssa External flood list length 0 Area BACKBONE(0) Number of interfaces in this area is 3 Area has no authentication SPF algorithm executed 7 times Area ranges are Number of LSA 3. Checksum Sum 0x01e35c Number of opaque link LSA 0. Checksum Sum 0x Number of DCbitless LSA 0 Number of indication LSA 0 Number of DoNotAge LSA 0 Flood list length 0 Task 4: Configure OSPF Router IDs The OSPF router ID is used to uniquely identify the router in the OSPF routing domain. A router ID is usually an IP address. Cisco routers derive the router ID in one of three ways and with the following precedence:- 1. IP address configured with the OSPF router-id command. 2. Highest IP address of any of the router s loopback addresses. 3. Highest active IP address on any of the router s physical interfaces. 7

8 Step 1. Examine the current router IDs in the topology. (The router ID can also be seen in the output of the show ip protocols, show ip ospf, and show ip ospf interfaces commands):- What is the router ID for R1? What is the router ID for R2? What is the router ID for R3? Step 2. Use interface loopback <loopback_number> to change the router IDs of the routers in the topology. R1(config)# interface loopback 0 R1(config-if)# ip address R1(config)# end R1# R2(config)# interface loopback 0 R2(config-if)# ip address R2(config)# end R2# R3(config)# interface loopback 0 R3(config-if)# ip address R3(config)# end R3# Step 3. Reload the routers to force the new router IDs to be used. When a new router ID is configured, it will not be used until the OSPF process is restarted. Make sure that the current configuration is saved to NRAM, and then use the reload command to restart each of the routers. When the router is reloaded, what is the router ID for R1? When the router is reloaded, what is the router ID for R2? When the router is reloaded, what is the router ID for R3? Step 4. Use Ping command to ping from PC1 to PC2 and PC3, and vice versa. Is these pings are successful? If not debug your configurations on the routers. Task 5: Documentation On each router, save the running configuration using (copy running-config startupconfig) command, then save your Packet Tracer's file. 8

9 Practice2 (Homework):- Scenario: You have built a network for a company, which had the following configurations: Device Interface IP Address Subnet Mask Default Gateway Description R1 Fa0/ R1 LAN Se 0/0/ Link to R2 Se 0/0/ Link to R3 R2 Fa 0/ R2 LAN1 Fa 0/ R2 LAN2 Se 0/0/ Link to R1 Se 0/0/ Link to R3 R3 Fa 0/ R3 LAN Se 0/0/ Link to R1 Se 0/0/ Link to R2 PC0 NIC PC1 NIC PC2 NIC PC3 NIC Laptop0 NIC Laptop1 NIC Also to mentioned that all the routers have (cisco) as a console password and (class) for the privilege mode. (You have to write the descriptions EXACTLY as shown in the table). Now you have to further configure the routers to actually route the packets between the networks. In this lab homework, you will use OSPF routing protocol to construct the routing tables. Task 1: Configure Interfaces and PCs Use the table above as a guide to configure all the interfaces and the PCs. Task 2: Configure OPSF Routing Use the table above as a guide to configure all the interfaces and the PCs. Step 1. Configure OSPF routing on R1 R1(config)#router ospf 1 R1(config-router)# R1(config-router)#network area 1 R1(config-router)#network area 0 R1(config-router)#network area 0 R1(config-router)#end R1# Step 2. Configure RIP routing on R2 R2(config)#router ospf 1 R2(config-router)# R2(config-router)#network area 2 R2(config-router)#network area 3 R2(config-router)#network area 0 R2(config-router)#network area 0 R2(config-router)#end R2# 9

10 Step 3. Configure OSPF routing on R3 R3(config)#router ospf 1 R3(config-router)# R3(config-router)#network area 4 R3(config-router)#network area 0 R3(config-router)#network area 0 R3(config-router)#end R3# Task 3: Verify OSPF Routes Step 1. On each router use the show ip route, show ip ospf, show ip ospf interface and show ip protocols to verify that OSPF is working. (Write down the routes on external paper for the three routers and deliver it to your teacher) Task 4: Verify OSPF Routing Use Ping command to ping from PC0 to Laptop1, PC2 to PC1, PC1 to PC3, PC2 to Laptop0 and from PC1 to PC0. Are all these pings were successful? Please make sure that the completion percentage is 100% at this stage (without a * mark which means that there is an error on some routes), else you have to go back and verify your network settings. Also, don't forget to save the file and rename it to be LAB4-XXXX, where XXXX represents your student number. 11