CN_IT2050_L4_routing.pdf

IT2050 - Computer Networks Lecture 3 Routing Protocols Ms. Hansika Mahaadikara IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara 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. 10.120.2.0 172.16.1.0 IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara What Is Routing? (cont.) 10.120.2.0 172.16.1.0 E0 S0 Network Destination Exit Protocol Network Interface Connected 10.120.2.0 E0 Routed Protocol: IP Learned 172.16.1.0 S0 Routers must learn destinations that are not directly connected. IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Identifying Static & Dynamic Routes Static Route Dynamic Route Uses a route that a network Uses a route that a network routing administrator enters into the protocol adjusts automatically for router manually topology or traffic changes IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Direct Delivery Send a message to a machine in the SAME LAN IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Indirect Delivery IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Indirect Delivery cont. To send a packet from source to destination, need to go to the network ( packet should go from router to router ) All routers should maintain a routing table IP packet is analyzed at the router and correct path is selected form the routing table The packet is sent though that path Indirect delivery is done using the routing strategies IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Routing Table IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Adaptive Routing Routing Strategies There are four routing strategies - Fixed Routing - Flooding - Random Routing - IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Adaptive Routing Each router maintains a routing table Routing table modifies itself according to the network changes Advantages - Network traffic is minimized - Low latency - The best route will be selected most Disadvantages - Router memory need to keep a routing table IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Routing Methods used in Adaptive Routing Next hop routing Host specific Network specific Default routing IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Host Specific Routing Each router keeps one record/entry for each Table entry has Host IP and the Interface Host Address Interface 192.168.50.1 E0 192.168.50.6 E0 172.18.2.9 S1 172.18.5.96 S1 Disadvantages Large number of records Table updating is difficult and complex as it should be done for each and every host (if the host IP changes) IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Network Specific Routing Each router keeps a table entry for each network (one record for one network) Table entry has Network address and Interface Network Address Interface 192.168.50.0 E0 172.18.0.0 S1 Advantages Number of records are limited (Table updates are not for each host but for a network) Update is easy IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Routing Table update Methods Basic methods to update routing tables - Connected - Static - Dynamic IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Connected Once the router is connected to the network its interfaces are given IP addresses With that router automatically identifies the network addresses to which it connected IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Connected cont. R1#show ip route Codes: C - connected, S - static, Gateway of last resort is not set 172.16.0.0/24 is subnetted, 2 subnets C 172.16.2.0 is directly connected, Serial0/0/0 C 172.16.3.0 is directly connected, FastEthernet0/0 IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Static Administrator can manually give routing table records Router(config)#ip route IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Static cont. R1(config)# R1(config)#ip route 172.16.1.0 255.255.255.0 172.16.2.2 R1(config)#ip route 192.168.1.0 255.255.255.0 172.16.2.2 R1(config)#ip route 192.168.2.0 255.255.255.0 172.16.2.2 R1(config)# R1#show ip route Codes: C - connected, S - static Gateway of last resort is not set 172.16.0.0/24 is subnetted, 3 subnets S 172.16.1.0 [1/0] via 172.16.2.2 C 172.16.2.0 is directly connected, Serial0/0/0 C 172.16.3.0 is directly connected, FastEthernet0/0 S 192.168.1.0/24 [1/0] via 172.16.2.2 S 192.168.2.0/24 [1/0] via 172.16.2.2 IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Static cont. Advantages: Minimal CPU processing Easier for administrator to understand and configure Disadvantages: Configuration and maintenance is time-consuming Configuration is error-prone Administrator should maintain changing route information Does not scale well with growing networks; maintenance becomes complex Requires complete knowledge of the whole network for proper implementation IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Default Routing Last record in the routing table Indicates the route/path to be taken, if any of the records does not match with the IP packet destination IP address Stub networks only use default routing , Stub networks have only one exit port out of the network R(config)#ip route 0.0.0.0 0.0.0.0 IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Default Routing cont. B(config)# B(config)#ip route 0.0.0.0 0.0.0.0 172.16.2.2 B(config)# B#show ip route Codes: C - connected, S - static Gateway of last resort is 172.16.2.2 to network 0.0.0.0 172.16.0.0/24 is subnetted, 2 subnets C 172.16.1.0 is directly connected, FastEthernet0/0 C 172.16.2.0 is directly connected, Serial2/0 S* 0.0.0.0/0 [1/0] via 172.16.2.2 B# IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Dynamic Routing Scenario IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Dynamic Routing Scenario IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Dynamic Routing tables are updated automatically by using routing protocols Routing tables have Initially only connected records Then add static’ records Then automatic dynamic updates IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Dynamic cont. Advantages: Administrator has less work maintaining the configuration when adding or deleting networks Protocols automatically update, according to the topology changes. Configuration is less error-prone Suitable for More scalable, growing networks Disadvantages: Router resources are used (CPU cycles, memory and bandwidth) More administrator knowledge is required for configuration, verification, and troubleshooting IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Routing Protocols IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Features of Routing Protocols Network changes (addition or removal or fault) are automatically updated in routing tables of all routers When there are many routes to a destination, the best route should be selected Share the traffic through different routes IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara What Is a Routing Protocol? Routing Protocols 10.120.2.0 172.16.1.0 allow routers to E0 S0 dynamically advertise and learn routes, determine which routes are available and which are the Network Protocol Destination Network Exit Interface 172.17.3.0 most efficient routes Connected 10.120.2.0 E0 to a destination RIP 172.16.2.0 S0 EIGRP 172.17.3.0 S1 Routing Protocol: RIP, EIGRP,OSPF IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Routing Protocols IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Routing Protocols cont. An autonomous system (AS) is a collection of routers under a common administration ex : a company's internal network Interior Gateway Protocols (IGP) are used for intra-autonomous system routing (routing inside an autonomous system) Exterior Gateway Protocols (EGP) are used for inter-autonomous system routing (routing between autonomous systems) IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Routing Protocols cont. IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Interior Gateway Protocols (IGP) IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara RIP (Routing Information Protocol) IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara RIP (Routing Information Protocol) A Distance-vector routing protocol It sends the complete routing table out to all active interfaces in every 30 seconds Only uses hop count to select best way to a remote network RIP works well in small networks, but it is inefficient on large networks There are two versions RIP v1, RIP v2 IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara RIP Configuration Router(config)#router rip Router(config-router)#network < network-address> Directly connected network addresses IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara RIP Configuration Example Version 1 E0 S0 S1 S0 S1 E0 172.16.0.0 A 192.168.1.0 B C 172.16.0.1 10.0.0.1 10.0.0.2 11.0.0.1 11.0.0.2 192.168.1.1 router rip 2.3.0.0 router rip 2.3.0.0 network 172.16.0.0 network 192.168.1.0 network 10.0.0.0 network 11.0.0.0 router rip network 10.0.0.0 Network 11.0.0.0 IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Configure RIP V2 Classless Sub-networks Router(config)#router rip Router(config)#version 2 Router(config-router)#network < network-address> : Directly connected sub-network addresses IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara RIP Configuration Example Version 2 E0 S0 S1 S0 S1 E0 172.16.64.0 A 192.168.1.128 B C 172.16.64.1 10.0.1.1 10.0.1.2 10.0.2.1 10.0.2.2 192.168.1.129 router rip router rip Version 2 Version 2 No auto-summary No auto-summary network 172.16.64.0 network 192.168.1.0 network 10.0.1.0 network 10.0.2.0 router rip Version 2 No auto-summary network 10.0.1.0 Network 10.0.2.0 IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Displaying the IP Routing Table 10.0.1.2 E0 S0 S1 S0 S1 E0 172.16.64.0 A 192.168.1.128 B C 10.0.1.0 10.0.2.0 RouterA#sh ip route Codes: C - connected, S - static, I - IGRP, R – RIP 172.16.0.0/16 is subnetted, 1 subnets C 172.16.64.0 is directly connected, Ethernet0 10.0.0.0/8 is subnetted, 2 subnets R 10.0.2.0/24 [120/1] via 10.0.1.2, 00:00:07, Serial0 C 10.0.1.0/24 is directly connected, Serial0 R 192.168.1.128/26 [120/2] via 10.0.1.2, 00:00:07, Serial2 IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara RIP Timers Periodic Timer - A timer kept at each router for sending its routing table information to its neighbors in every 30 seconds. Expiration Timer - If a router does not get the updates from a neighboring router for a long time ,( means it is a problem with the neighboring router) the main router removes the updates got from that neighboring router - Is called expiration time ( 180 seconds ) IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Problems with RIP Slow Convergence Routing tables are sent to neighbors every 30 seconds When there are large number of routers in the network ,it will take some time to get all the details to each and every router.There is a delay in getting an updated routing table. Solution Triggered updates Information that needed to be updated immediately is informed to the other routers without waiting for the periodic time. IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Counting to infinity Solution - Route Poisoning When a network goes down the router that is connected to that network will get that information first So that router updates its table saying this network is down (unreachable ) In the routing table it says number of hops for that particular network as infinity (or in RIP as 16) IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Instability Once a router (P) get some updates from other router (Q) router P will updates it routing table and new routing table sent again to previous router. With time this will lead to having wrong updated tables in the routers and ultimately to an unstable situation Solution Spilt Horizon - Do not send same information via the link which that information came from IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Solutions Split Horizon When the router sends routing table information to the neighbors, it will not send the information that it got from that particular router So the routing table information will be selected and send IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Hold down Timer Once a network goes down, that information will be immediately sent to the other routers Because of the network connections there is a possibility to get some wrong information about that particular network from other routers Therefore once a network down information is received, the router will start the hold down timer, during which time any updates regarding that particular network is ignored. IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Poison Reverse In general split horizon will apply for information passing But the split horizon will not be applied in the case of the information like network is down IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara IGRP AD - 100 (Interior Gateway Routing Protocol ) A cisco proprietary distance-vector routing protocol Maximum hop count is 255 Used in large networks EIGRP is the enhanced version of IGRP IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara EIGRP IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara EIGRP (Extended Interior Gateway Routing Protocol ) IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara Features EIGRP was initially released in 1992 as a proprietary protocol available only on Cisco devices. In 2013, Cisco released a basic functionality of EIGRP as an open standard to the IETF as an informational RFC. Other networking vendors can now implement EIGRP on their equipment to interoperate with both Cisco and non-Cisco routers running EIGRP. IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara EIGRP Metric AD - 90 A ‘ Composite metric ‘ is used EIGRP uses bandwidth and delay of the line by default as a metric for determining the best route to an internetwork Metric is a combination of bandwidth, delay of the line , Reliability, load and Maximum Transmission Unit (MTU) Reliability, load, and Maximum Transmission Unit (MTU) are not used by default IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara EIGRP metric values Bandwidth - The slowest bandwidth among all of the outgoing interfaces, along the path from source to destination. Delay - The cumulative (sum) of all interface delay along the path (in microseconds). IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara EIGRP Configuration Router(config)#router Eigrp Router(config-router)#network < network address > : Directly connected network addresses < AS number > : Autonomous Systems Number IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara EIGRP Configuration Example E0 S0 S1 S0 S1 E0 172.16.64.0 A 192.168.1.128 B C 172.16.64.1 10.0.1.1 10.0.1.2 10.0.2.1 10.0.2.2 192.168.1.129 router eigrp 100 router eigrp 100 No auto-summary network 172.16.64.0 network 192.168.1.0 network 10.0.1.0 network 10.0.2.0 No auto-summary router eigrp 100 No auto-summary network 10.0.1.0 Network 10.0.2.0 IT2050| Computer Networks| Routing Protocols| Hansika Mahaadikara

CN_IT2050_L4_routing.pdf

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