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CCNA 2 v3. 1 Module 6

CCNA 2 v3. 1 Module 6. CCNA 2. Module 6 Routing & Routed Protocols. Introducing Routing. R outers must learn the direction to remote networks in order to forward packets. There are 2 ways to learn this information: Dynamic Routing Static Routing Routers use the routing process to

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CCNA 2 v3. 1 Module 6

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  1. CCNA 2 v3.1 Module 6

  2. CCNA 2 Module 6 Routing & Routed Protocols

  3. Introducing Routing • Routers must learn the direction to remote networks in order to forward packets. • There are 2 ways to learn this information: • Dynamic Routing • Static Routing • Routers use the routing process to • Forward packets toward the destination network • Decisions based upon the destination IP address • Dynamic routing • Routers learn information from other routers • Scalable – each change learned from another router • Static routing

  4. Static Routing • Configured manually by the network administrator • Add and remove static routes when topology changes • Static Route Operations are divided into three parts: • Network administrator configures the route • Router installs the route in the routing table • Packets are routed using the static route • Command • Router#config terminal • Router(config)#ip route • Router(config)#ip route destinationsubnetoutgoing • networkmaskinterface • or • next • hop

  5. Static Routes using Outgoing Interface Specifies Outgoing Interface

  6. Static Route Using Next Hop Specifies Next Hop

  7. The Difference between the 2 options is • Administrative distance assigned to the route • Administrative distance • Optional • Measures the reliability of the route (0 – 255) • The lower the number the more reliable the route • Set to 1 for next hop • Set to 0 for outgoing interface • Routers choose the route with the lowest administrative distance

  8. To set a static route that is not 1 or 0 • ip route 130 • Static routes • Can be used as a backup if dynamic route fails • Must have higher admin no. to dynamic route Try the interactive media lab CCNA 2 Module 6 Page 6.1.2 Try the interactive media lab CCNA 2 Module 6 Page 6.1.3

  9. Configuring a Default Route • Default routes • Route packets with destinations that do not match any of the other routes in the routing table • Often used for • internet-bound traffic • Non-directly connected networks • Special form of a static route • ip route [next-hop-addressoroutgoing if] • Example ip route s0 Try the interactive media lab CCNA 2 Module 6 Page 6.1.4

  10. Verifying static route configuration • show running-config • Views the active configuration in RAM to verify that the static route was entered correctly • show ip route • Make sure that the static route is present in the routing table • Ping <ip address> • check a connection • Traceroute <ip address> • Shows the path to the ip address • Can be used to identify where the connection fails Try Interactive media labs CCNA 2 Module 6 Page 6.1.5

  11. Dynamic Routing

  12. Routing Protocols • Allow routers to share information with other routers regarding • the networks it knows about • its proximity to other routers • Used to build and maintain a routing table • Examples: • Routing Information Protocol - RIP • Interior Gateway Routing Protocol - IGRP • Enhanced Interior Gateway Routing Protocol -EIGRP • Open Shortest Path First - OSPF

  13. Routed Protocol • Directs user traffic • Provides enough information in its network layer address to allow a packet to be forwarded from one host to another based on the addressing scheme • Internet Protocol (IP) • Internetwork Packet Exchange (IPX)

  14. Autonomous Systems • A collection of networks under • a common administration – e.g., MBNA_Europe • sharing a common routing strategy • American Registry of Internet Numbers -ARIN • Assigns an identifying number to each AS • It is a 16 bit number • IGRP and EIGRP have autonomous system numbers

  15. Purpose of a routing protocol and autonomous systems • Routing protocol • Learns all available routes • Places the best routes into the routing table • Removes routes that are no longer valid • Router use information in the routing table • To forward routed protocol packet • Routing protocols change/update routing tables • When the network topology changes • Internetwork is converged when • All routers in an internetwork are operating with the same knowledge • Fast convergence is desirable

  16. Classes of routing protocols • Distance vector • Uses distance and direction • Link-state • Shortest path first • Recreates the exact topology of the entire internetwork

  17. Distance vector routing protocol features • Router passes periodic copies of a routing table • to directly connected router • These updates communicate topology changes • Updates do not allow router to know exact internetwork topology • it only sees its neighbours routers • Also called Bellman-Ford algorithms • When a router receives an update where there is an information change • It uses this information to alter the distance and update the routing table

  18. Distance Vector Concept

  19. Link-state routing protocol features • Link-state algorithms are also known as • Dijkstras algorithm • or SPF (shortest path first) algorithms • A link-state routing algorithm • Maintains a complete database of the topology • A full knowledge of distant routers and how they interconnect

  20. Link State Routing use • Link-state advertisements (LSAs) • A small packet of routing information sent between routers • Topological database • A collection of information gathered from LSAs. • SPF algorithm (shortest path first) • A calculation performed on the database resulting in the SPF tree • Routing tables • A list of the known paths and interfaces

  21. Link State Routing Protocol Features • Network discovery processes for link state routing • LSAs are exchanged between directly connected routers with information about directly connected networks • These LSAs are accumulated on each router and a topological database is constructed • The SPF algorithm uses this database to calculate shortest path • It then builds a tree, with itself as the root, consisting of all possible paths to each network • It sorts these paths Shortest Path First (SPF) • Lists the best paths and ports to these destination networks in the routing table

  22. To achieve convergence • Each router keeps track of its neighbor routers • Router, Name, Interface status, Cost of the link • The first router to become aware of a topology change • Forwards the information to all other routers • Using a Link State Advertisement (LSA) • When a router receives a LSA it • It adds the information to the routers database and the SPF algorithm is run again • Link-state concerns: • Processor overhead • Memory requirements • Bandwidth Consumption

  23. Path determination • A router determines the path using: • A path determination function • A switching function • Path determination • Occurs at network layer • Router uses the routing table to determine the best path • Switching • Router accepts a packet on one interface and forward it to a second interface on the same router • Router encapsulates the packet in the appropriate frame type for the next data link

  24. Routing Configuration • To enable IP routing protocol on a router • Setting global parameters • and routing parameters • Global tasks • Selecting a routing protocol (RIP, IGRP, EIGRP or OSPF) • Specify the network • Routing metric • Help routers find the best path to each network

  25. Command Layout • Router(config)#router <protocol> <option> • Router(config-router)#network <network no> • <protocol> e.g., rip, igrp, ospf… • <option> e.g., autonomous system no • <network no> directly connected network • Commands • Router(config)# router rip • Router(config-router)#network Try lab activity CCNA 2 Module 6 Page 6.3.2

  26. Routing Protocols • RIP – Distance vector interior routing protocol • IGRP – Cisco's distance vector interior routing protocol • OSPF – A link-state interior routing protocol • EIGRP – Cisco’s advanced distance vector interior routing protocol • BGP – A distance vector exterior routing protocol

  27. Routing Information Protocol (RIP) • Originally specified in RFC 1058 • Interior gateway protocol • Distance vector routing protocol • Metric for path selection is hop count • If hop count is greater than 15, packet discarded • Routing updates broadcast every 30 seconds • Interior Gateway Routing Protocol (IGRP) • Proprietary protocol developed by Cisco • Distance vector routing protocol • Metrics used are • Bandwidth, load, delay and reliability • Routing updates broadcast every 90 seconds

  28. Open Shortest Path First (OSPF) • Nonproprietary CISCO protocol • Link-state routing protocol • Originally described in RFC 2328. • Uses SPF algorithm to calculate the lowest cost to a destination • Routing updates are flooded as topology changes occur

  29. EIGRP - Enhanced Interior Gateway Routing Protocol • Cisco proprietary protocol • Enhanced distance vector routing protocol • Uses load balancing • Combination of distance vector and link-state • Calculates shorted path first using Diffused Update Algorithm (DUAL) • Routing updates • Broadcast every 90 seconds • or as triggered by topology changes

  30. Border Gateway Protocol (BGP) • Exterior Gateway Protocol • Distance vector routing protocol • Used between ISPs or ISPs and clients • Used to route Internet traffic between autonomous systems Try Interactive Lab CCNA 2 Module 6 Page 6.3.3

  31. Exterior Gateway Protocols • EGP designed for use between • two different networks that are under the control of different organizations, ISPs. • In order for routing to begin you need: • A list of neighbor routers with which to exchange routing information • A list of networks to advertise as directly reachable • The autonomous system number of the local router Try interactive lab CCNA 2 Module 6 Page 6.3.4

  32. Distance vector (RIP or IGRP) • Known as Bellman-Ford algorithm • Routing decisions based upon information provided by its neighboring routers • Inform neighbors of your routing table on periodic basis • Advantages • use few resources • Disadvantages • Slow convergence • Metrics don’t scale well • Decisions made based on • Finding the distance (number of hops) • and vector (direction) to any link on the internetwork

  33. Link-state (OSPF or IS-IS) • Shortest Path First algorithm • Flood routing information to all routers • Each router gets a complete view of internetwork • Routing updates sent on topology change (LSA) • They are event triggered • Resulting in quick convergence • Quick convergence • Prevents routing loops • Prevents routing errors • Use more system resources • Expensive to implement but scalable

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