1. Chapter 3 Dynamic Routing Protocols CIS 82 Routing Protocols and Concepts Rick Graziani Cabrillo College graziani@cabrillo.edu Last Updated: 3/3/2009

2. 2 Note This presentation will be updated prior to March. 25, 2008 The audio of the lecture for this presentation will be available on my web site after March. 25, 2008 My web site is www.cabrillo.edu/~rgraziani. For access to these PowerPoint presentations and other materials, please email me at graziani@cabrillo.edu.

3. 3 For further information This presentation is an overview of what is covered in the curriculum/book. For further explanation and details, please read the chapter/curriculum. Book:  Routing Protocols and Concepts  By Rick Graziani and Allan Johnson  ISBN: 1-58713-206-0  ISBN-13: 978-58713- 206-3

4. 4 Topics Introduction to Dynamic Routing Protocols  Perspective and Background  Network Discovery and Routing Table Maintenance  Dynamic Routing Protocol Advantages Classifying Dynamic Routing Protocols  IGP and EGP  Distance Vector and Link- State  Classful and Classless  Convergence Metrics  Purpose of the Metric  Metrics and Routing Protocols  Load Balancing Administrative Distance  Purpose of Administrative Distance  Dynamic Routing Protocols and Administrative Distance  Static Routes and Administrative Distance  Directly Connected Networks and Administrative Distance

5. Introduction to Dynamic Routing Protocols Perspective and Background Network Discovery and Routing Table Maintenance Dynamic Routing Protocol Advantages

6. 6 Perspective and Background Dynamic routing protocols have evolved over several years As networks have evolved and become more complex, new routing protocols have emerged. Most institutions have migrated to new protocols, others are still in use.

7. 7 Perspective and Background Interior Routing Protocols or Interior Gateway Protocols (IGP) Distance Vector  RIPv1 – Simple, Classful, limited metrics (hop count)  RIPv2 – Simple, Classless, limited metrics (hop count) Cisco Proprietary  IGRP – Simple, Classful, better metric (BW, delay, reliab., load)  EIGRP – Simple, Classless, same metric, DUAL (backup routes) Link State  OSPF – Perceived complex, classless, Cisco metric BW, IETF  IS-IS - Perceived complex, classless, metric “default”, ISO Classful (does not support CIDR and VLSM) Classless (supports CIDR and VSLM)

8. 8 Perspective and Background Exterior Routing Protocols or Exterior Gateway Protocols (EGP) Border Gateway Protocol (BGP)  Between ISPs (Internet service providers)  Between ISPs and their larger private clients  Path Vector routing protocol, metric – attributes (policies)  Replaced EGP

9. 9 Role of Dynamic Routing Protocol Dynamic Routing Protocols:  Exchange of routing information between routers  Dynamically learn information about remote networks  Determines the best path to each network  Automatically learn about new networks  Automatically finds alternate paths if needed (link failure in current path) Update

10. 10 Role of Dynamic Routing Protocol What is an advantage of dynamic routing protocols compared to static routes?  Less administrative overhead (change modifications)  More work and more chances to make a mistake. Make additions, deletions, and modifications to static routes! Add new static routes… Static Routes

11. 11 Role of Dynamic Routing Protocol Change in network using a dynamic routing protocol. Dynamic routing protocols automatically adjust to changes in the network:  New networks  Deleted networks  Changes in topology Configuration is less error-prone Scales better with larger networks No changes! Add dynamic routing protocol… Dynamic Routing Protocol

12. 12 Role of Dynamic Routing Protocol Disadvantages of using Dynamic routing protocol  More CPU and memory requirements (not usually a problem)  This is not that big an issue in most networks and with modern routers.  “Less secure” if routing updates are sent unencrypted. Most networks use both dynamic and static routes

13. 13 Purpose of Dynamic Routing Protocols A routing protocol is a set of processes, algorithms, and messages that are used to exchange routing information and populate the routing table with the routing protocol’s choice of best paths. Components of a routing protocol (depending upon the routing protocol):  Data structures: Tables or databases for their operations, kept in RAM.  Algorithm:  Routing protocols use algorithms for processing routing information and for best-path determination.  Routing protocol messages:  Discover neighboring routers  Exchange routing information  Learn and maintain accurate information about the network I’m R1 I’m R3 My routes Changes

14. 14 Dynamic Routing Protocol Operation The operations of a dynamic routing protocol vary depending on the type of routing protocol, but in general: 1. The router shares routing messages and routing information with other routers that are using the same routing protocol. 2. The router sends and receives routing messages on its interfaces. 3. Routers exchange routing information to learn about remote networks. 4. When a router detects a topology change, the routing protocol can advertise this change to other routers. Update I’m running RIP and will share with other routers running RIP. I’m running RIP too. I just learned about remote networks from R2 and R3. I just learned about remote networks from R1 and R3. I just learned about remote networks from R1 and R2. X I no longer have a connection to this network! Got it, I will tell R3… Got it!

15. 15 Static Routing Usage, Advantages, and Disadvantages When would you use a static route?  With smaller networks that are not expected to grow significantly.  Routing to and from stub networks  Default route

16. Classifying Dynamic Routing Protocols IGP and EGP Distance Vector and Link-State Classful and Classless Convergence

17. 17 Classifying Routing Protocols Routing Protocols can be classified by:  IGP or EGP  Distance vector or link-state  Classful or classless

18. 18 IGP and EGP An autonomous system (AS)—otherwise known as a routing domain—is a collection of routers under a common administration.  Company’s internal network  An ISP’s network. Because the Internet is based on the autonomous system concept, two types of routing protocols are required:  Interior routing protocols: Within Cabrillo College & within CENIC  Routing inside an autonomous system  Exterior routing protocols: Between ISPs, CENIC and PAIX  Routing between autonomous systems PAIX Palo Alto CENIC BGP Cabrillo College

19. 19 Distance Vector and Link-State Routing Protocols Interior gateway protocols (IGP) can be classified as two types:  Distance vector routing protocols  Link-state routing protocols

20. 20 Distance Vector Routing Protocol Operation What does a street sign like this tell you?  How far (distance)  Which way (direction) Distance vector  Routes are advertised as vectors of distance and direction. Distance is defined in terms of a metric  Such as hop count Direction is simply the:  Nexthop router or  Exit interface Typically use the Bellman-Ford algorithm for the best-path (shortest) route determination

21. 21 Distance Vector Routing Protocol Operation Routing protocol  Does not know the topology of an internetwork.  Only knows the routing information received from its neighbors.  Does not know if another path would actually be faster. I don’t have a map of the network. All I know is how far and which direction (to next hop router) Distance Vector routing protocols are like signposts along the path to the final destination. Would another path that is longer actually be faster? (speed limit)

22. 22 Distance Vector Routing Protocol Operation Where might you use a distance vector routing protocol?  Simple and flat network  The administrators do not have enough knowledge about link-state protocols.  Specific types of networks, such as hub-and-spoke networks, are being implemented.  Worst-case convergence times in a network are not a concern. More in Chapter 4.

23. 23 Link-State Protocol Operation Link-state routing protocol can create a “complete view,” or topology, of the network. Link-state protocols are associated with Shortest Path First (SPF) calculations. A link-state router uses the link- state information to:  Create a topology map  Select the best path to all destination networks in the topology.  Each router makes the decision! Link State routing protocols is like having a complete map of the network topology OR

24. 24 Link-State Protocol Operation Link-state protocols work best in situations where  The network design is hierarchical, usually occurring in large networks.  The administrators have a good knowledge of the implemented link-state routing protocol.  Fast convergence of the network is crucial. More in later chapters.

25. 25 Classful and Classless Routing Protocols All routing protocols can also be classified as either  Classful routing protocols  Classless routing protocols  IPv6 routing protocols are classless

26. 26 Classful Routing Protocols Classful routing protocols do NOT send subnet mask information in routing updates.  The first routing protocols, such as RIP  When network addresses were allocated based on classes.  Class A, B, or C.  Network mask determined based on value of first octet of the network address. 172.16.0.0 192.168.1.0 192.168.2.0

27. 27 Classful Routing Protocols Classful routing protocols do not include the subnet mask  Therefore do not support VLSM and CIDR.  All subnets within the same “major classful network address” must have the same mask. More later! 172.16.0.0/16 Major Classful Network

28. 28 Classless routing Protocols Today’s networks are no longer allocated based on classes  Subnet mask cannot be determined by the value of the first octet. Classless routing protocols include the subnet mask with the network address in routing updates. 172.16.0.0/28 192.168.1.0/24 192.168.2.0/30 172.16.1.0/28 192.168.1.0/24 192.168.2.4/30

29. 29 Classless routing Protocols Classless routing protocols are required in most networks today because of their support for:  VLSM  CIDR  Discontiguous networks. 172.16.128.0/30172.16.132.0/30 172.16.136.0/30 172.16.0.0/16 Major Classful Network /27 and /30 subnets

30. 30 Convergence is when the routing tables of all routers are at a state of consistency.  Network has converged: When all routers have complete and accurate information about the network. Convergence time is the time it takes routers to:  Share information  Calculate best paths  Update their routing tables A network is not completely operable until the network has converged; therefore, most networks require short convergence times. Dynamic Routing Protocols and Convergence X I no longer have a connection to this network! Got it, I will tell R3… Got it!

31. 31 Dynamic Routing Protocols and Convergence Generally, convergence time:  Slow: RIP and IGRP  Faster: EIGRP, OSPF, and IS-IS R2’s Routing Table R1’s Routing Table R3’s Routing Table

32. Metrics Purpose of the Metric Metrics and Routing Protocols Load Balancing

33. 33 Purpose of a Metric Metrics are a way to measure or compare.  Determine the best path. Routing protocol learns multiple routes to the same destination.  Metric is used to determine which path is most preferable ?

34. 34 Purpose of a Metric What might be some ways (metrics) that routing protocols might use to determine the “best path? Routing protocol metrics:  RIP: Hop count  IGRP and EIGRP: Bandwidth, delay, reliability and load  OSPF (Cisco’s version): Bandwidth  IS-IS: Four values (Cisco uses “default”) – Covered in CCNP  BGP: Attributes – Covered in CCNP More later

35. 35 Metric Parameters R1 to reach the 172.16.1.0/24 network. RIP: Fewest number of hops via R2. OSPF: Path with the highest cumulative bandwidth through R3.  This results in faster packet delivery. 56 Kbps

36. 36 Metric Field in the Routing Table The routing table displays the metric for each dynamic and static route.  Static routes always have a metric of 0. Routing protocols install route in routing table with the lowest metric. R2# show ip route 172.16.0.0/24 is subnetted, 3 subnets C 172.16.1.0 is directly connected, FastEthernet0/0 C 172.16.2.0 is directly connected, Serial0/0/0 C 192.168.1.0/24 is directly connected, Serial0/0/1 S 192.168.2.0/24 [1/0] via 192.168.1.1 R 192.168.7.0/24 [120/1] via 192.168.4.1, Serial0/0/1 R 192.168.8.0/24 [120/2] via 192.168.4.1, Serial0/0/1

37. 37 All routers running RIP What is the metric for R2 to reach the 192.168.8.0 network?  2 (hops away) R2# show ip route Gateway of last resort is not set R 192.168.1.0/24 [120/1] via 192.168.2.1, 00:00:24, Serial0/0/0 C 192.168.2.0/24 is directly connected, Serial0/0/0 C 192.168.3.0/24 is directly connected, FastEthernet0/0 C 192.168.4.0/24 is directly connected, Serial0/0/1 R 192.168.5.0/24 [120/1] via 192.168.4.1, 00:00:26, Serial0/0/1 R 192.168.6.0/24 [120/1] via 192.168.2.1, 00:00:24, Serial0/0/0 [120/1] via 192.168.4.1, 00:00:26, Serial0/0/1 R 192.168.7.0/24 [120/1] via 192.168.4.1, 00:00:26, Serial0/0/1 R 192.168.8.0/24 [120/2] via 192.168.4.1, 00:00:26, Serial0/0/1

38. 38 What happens when two or more routes to the same destination have identical metric values?  The router load balances between these equal-cost paths.  All routing protocols do equal cost load balancing.  EIGRP also does unequal cost load balancing. Load Balancing R2# show ip route R 192.168.6.0/24 [120/1] via 192.168.2.1, 00:00:24, Serial0/0/0 [120/1] via 192.168.4.1, 00:00:26, Serial0/0/1

39. Administrative Distance Purpose of Administrative Distance Dynamic Routing Protocols and Administrative Distance Static Routes and Administrative Distance Directly Connected Networks and Administrative Distance

40. 40 Purpose of Administrative Distance What if a router learns about a remote network from two different routing sources. What if RIP advertises the network as 10 hops away but OSPF advertises it as a cumulative bandwidth of 100,000. Which is better RIP or OSPF?  Can’t tell  Can’t compare apples and oranges.  Note: This is not common. Administrative distance (AD) is:  Used to determine which routing source takes precedence.  Used when there are multiple routing sources for the same destination network address. Lower the AD the more preferred the routing source. RIP: 1.1.1.1. is 10 hops OSPF: 1.1.1.1. is 100,000 BW ? So, which one would be preferred RIP or OSPF? OSPF Which route would be preferred, OSPF or a Static Route to the same network? Static Route

41. 41 Purpose of Administrative Distance Cisco uses Administrative distance (AD) to define the preference of a routing source. Routing sources:  Directly connected networks  Static routes  Specific routing protocols AD for static and dynamic can be modifed (in CCNP) Note The term trustworthiness is commonly used when defining administrative distance. The lower the administrative distance value, the more trustworthy the route.

42. 42 Purpose of Administrative Distance AD: 0 to 255. The lower the value, the more preferred the route source. AD of 0 is the most preferred.  Only a directly connected network has an administrative distance of 0, which cannot be changed.  No better route to a network than being directly connected to that network. AD of 255 means the router will not believe the source of that route  Route will not be installed in the routing table.

43. 43 Verifying AD: show ip route R2# show ip route D 192.168.6.0/24 [90/2172416] via 192.168.2.1, 00:00:24, Serial0/0/0 What is the AD of this route? 90

44. 44 Verifying AD: show ip protocols R2# show ip protocols Routing Protocol is “eigrp 100 “ Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Default networks flagged in outgoing updates Default networks accepted from incoming updates EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0 EIGRP maximum hopcount 100 EIGRP maximum metric variance 1 Redistributing: eigrp 100 Automatic network summarization is in effect Automatic address summarization: Maximum path: 4 Routing for Networks: 192.168.2.0 192.168.3.0 192.168.4.0 Routing Information Sources: Gateway Distance Last Update 192.168.2.1 90 2366569 Distance: internal 90 external 170 <continued next slide?

45. 45 show ip protocols (continued) Routing Protocol is “rip” Sending updates every 30 seconds, next due in 12 seconds Invalid after 180 seconds, hold down 180, flushed after 240 Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Redistributing: rip Default version control: send version 1, receive any version Interface Send Recv Triggered RIP Key-chain Serial0/0/1 1 2 1 FastEthernet0/0 1 2 1 Automatic network summarization is in effect Maximum path: 4 Routing for Networks: 192.168.3.0 192.168.4.0 Passive Interface(s): Routing Information Sources: Gateway Distance Last Update 192.168.4.1 120 Distance: (default is 120) More on show ip protocols later

46. 46 Static Routes and Administrative Distance Static routes  Default AD = 1 After directly connected networks (AD = 0), static routes are the most preferred route source.

47. 47 Static Routes and Administrative Distance R2# show ip route 172.16.0.0/24 is subnetted, 3 subnets C 172.16.1.0 is directly connected, FastEthernet0/0 C 172.16.2.0 is directly connected, Serial0/0/0 S 172.16.3.0 is directly connected, Serial0/0/0 C 192.168.1.0/24 is directly connected, Serial0/0/1 S 192.168.2.0/24 [1/0] via 192.168.1.1 What is the AD of a Static Route? Static route: default AD = 1 (never 0)  Exit-interface: AD = 1  Next-hop IP address: AD = 1 After directly connected networks (AD = 0), static routes are the most preferred route source. Exit Interface: ip route 172.16.3.0 255.255.255.0 serial 0/0/0 Next-hop: ip route 192.168.2.0 255.255.255.0 192.168.1.1

48. 48 Static Routes and Administrative Distance R2# show ip route 172.16.0.0/24 is subnetted, 3 subnets C 172.16.1.0 is directly connected, FastEthernet0/0 C 172.16.2.0 is directly connected, Serial0/0/0 S 172.16.3.0 is directly connected, Serial0/0/0 C 192.168.1.0/24 is directly connected, Serial0/0/1 S 192.168.2.0/24 [1/0] via 192.168.1.1 The static route to 172.16.3.0 is listed as “directly connected”. It is common misconception to assume that the AD value of this route must be 0 because it states “directly connected a” - false assumption. Exit Interface: ip route 172.16.3.0 255.255.255.0 serial 0/0/0

49. 49 Static Routes and Administrative Distance R2# show ip route 172.16.3.0 Routing entry for 172.16.3.0/24 Known via “static”, distance 1, metric 0 (connected) Routing Descriptor Blocks: * directly connected, via Serial0/0/0 Route metric is 0, traffic share count is 1 View AD value this static route with an exit-interface, use command show ip route [route] option. Exit Interface: ip route 172.16.3.0 255.255.255.0 serial 0/0/0

50. 50 Directly Connected Networks and Administrative Distance To see the AD value of a directly connected network, use the command show ip route [route] option. R2# show ip route 172.16.3.0 Routing entry for 172.16.1.0/24 Known via “connected”, distance 0, metric 0 (connected, via interface) Routing Descriptor Blocks: * directly connected, via FastEthernet0/0 Route metric is 0, traffic share count is 1

51. 51 Floating Static Route (Extra) There are situations when an administrator will configure a static route to the same destination that is learned using a dynamic routing protocol, but using a different path. The static route will be configured with an AD greater than that of the routing protocol. If there is a link failure in the path used by the dynamic routing protocol, the route entered by the routing protocol is removed from the routing table. The static route will then become the only source and will automatically be added to the routing table. This is known as a floating static route and is discussed in CCNP courses. R2: ip route 192.168.8.0 255.255.255.0 192.168.2.1 5 R2: ip route 192.168.8.0 255.255.255.0 192.168.4.1 X

52. Chapter 3 Dynamic Routing Protocols CIS 82 Routing Protocols and Concepts Rick Graziani Cabrillo College graziani@cabrillo.edu Last Updated: 3/3/2009