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Routing

Routing. Anatomy of an IP Packet. IP packets consist of the data from upper layers plus an IP header. The IP header consists of the following:. Routing Protocol. Router. Switch. Router. Router. Router. Router. Switch. What is an optimal route ?. Path Determination Graphic.

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Routing

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  1. Routing

  2. Anatomy of an IP Packet IP packets consist of the data from upper layers plus an IP header. The IP header consists of the following:

  3. Routing Protocol Router Switch Router Router Router Router Switch What is an optimal route ?

  4. Path Determination Graphic

  5. Routing Protocols Routing protocols includes the following: processes for sharing route information allows routers to communicate with other routers to update and maintain the routing tables Examples of routing protocols that support the IP routed protocol are: RIP, IGRP, OSPF, BGP, and EIGRP.

  6. Routed Protocols Protocols used at the network layer that transfer data from one host to another across a router are called routed or routable protocols. The Internet Protocol (IP) and Novell's Internetwork Packet Exchange (IPX) are examples of routed protocols. Routers use routing protocols to exchange routing tables and share routing information. In other words, routing protocols enable routers to route routed protocols.

  7. Dynamic Routing Protocols • Function(s) of Dynamic Routing Protocols: • -Dynamically share information between routers. • -Automatically update routing table when topology changes. • -Determine best path to a destination.

  8. Dynamic Routing Protocols • The purpose of a dynamic routing protocol is to: • -Discover remote networks • -Maintaining up-to-date routing information • -Choosing the best path to destination networks • -Ability to find a new best path if the current path is no longer available

  9. Dynamic Routing Protocols • Components of a routing protocol • Algorithm • In the case of a routing protocol algorithms are used for facilitating routing information and best path determination • Routing protocol messages • These are messages for discovering neighbors and exchange of routing information

  10. Static Routing Static routing algorithms are basically table mappings established by the network administrator before the beginning of routing. These mappings do not change unless the network administrator alters them. Algorithms that use static routes are simple to design and work well in environments where network traffic is relatively predictable and where network design is relatively simple. Because of this fact, static routing systems cannot react to network changes. Static routes remain in the routing table even if the specified gateway becomes unavailable. If the specified gateway becomes unavailable, you need to remove the static route from the routing table manually. However, static routes are removed from th e routing table if the specified interface goes down, and are reinstated when the interface comes back up.

  11. Static Routing • Advantages of static routing • -It can backup multiple interfaces/networks on a router • -Easy to configure • -No extra resources are needed • -More secure • Disadvantages of static routing • -Network changes require manual reconfiguration • -Does not scale well in large topologies

  12. Configuring Static Routes Static routes are table mappings established by the network administrator before the beginning of routing. These mappings do not change unless the network administrator alters them. A static route uses this format: route if_namedest_ipmask gateway_ip [distance] Example: hostname(config)# route outside 10.10.10.0 255.255.255.0 192.168.1.1 [1]

  13. Configuring Default Routes Default routes are used to route packets with destinations that do not match any of the other routes in the routing table. A default route is actually a special static route that uses this format: ip route 0.0.0.0 0.0.0.0 [next-hop-address | outgoing interface] This is sometimes referred to as a “Quad-Zero” route. Example using next hop address: Router(config)#ip route 0.0.0.0 0.0.0.0172.16.4.1 Example using the exit interface: Router(config)#ip route 0.0.0.0 0.0.0.0s0/0

  14. Verifying StaticRoute Configuration After static routes are configured it is important to verify that they are present in the routing table and that routing is working as expected. The command show running-config is used to view the active configuration in RAM to verify that the static route was entered correctly. The show ip route command is used to make sure that the static route is present in the routing table.

  15. Classifying Routing Protocols • Dynamic routing protocols are grouped according to characteristics. Examples include: • -RIP • -IGRP • -EIGRP • -OSPF • -IS-IS • -BGP • Autonomous System is a group of routers under the control of a single authority.

  16. Classifying Routing Protocols • Types of routing protocols: • -Interior Gateway Protocols (IGP) • -Exterior Gateway Protocols (EGP)

  17. Classifying Routing Protocols • Interior Gateway Routing Protocols (IGP) • -Used for routing inside an autonomous system & used to route within the individual networks themselves. • -Examples: RIP, EIGRP, OSPF • Exterior Routing Protocols (EGP) • -Used for routing between autonomous systems • -Example: BGPv4

  18. EGP Exterior Gateway Protocols are used for routing between Autonomous Systems IGP Interior Gateway Protocols are used for routing decisions within an Autonomous System. Autonomous System An Autonomous System (AS) is a group of IP networks, which has a single and clearly defined external routing policy. AS 1000 AS 3000 AS 2000 Fig. 48 IGP and EGP (TI1332EU02TI_0004 The Network Layer, 67)

  19. Exterior Gateway Protocol (EGP) EGP EGP EGP Interior Gateway Protocol (IGP) Interior Gateway Protocol (IGP) AS 1000 AS 3000 IGP AS 2000 Fig. 49 The use of IGP and EGP protocols (TI1332EU02TI_0004 The Network Layer, 67)

  20. IGP and EGP An autonomous system is a network or set of networks under common administrative control, such as the cisco.com domain.

  21. Classifying Routing Protocols • IGP: Comparison ofDistance Vector & Link State Routing Protocols • Distance vector • routes are advertised as vectors • of distance & direction. • incomplete view of network • topology. • Generally, periodic • updates. • Link state • complete view of network • topology is created. • updates are not • periodic.

  22. Classifying Routing Protocols

  23. Classifying Routing Protocols • Classful routing protocols • Do NOT send subnet mask in routing updates • Classless routing protocols • Do send subnet mask in • routing updates.

  24. Classifying Routing Protocols • Convergence is defined as when all routers’ routing tables are at a state of consistency

  25. Routing Protocols Metrics • Metric • A value used by a routing protocol to determine which routes are better than others.

  26. Routing Protocols Metrics • Metrics used in IP routing protocols • -Bandwidth • -Cost • -Delay • -Hop count • -Load • -Reliability

  27. Routing Protocols Metrics • The Metric Field in the Routing Table • Metric used for each routing protocol • -RIP - hop count • -IGRP & EIGRP - Bandwidth (used by default), Delay (used by default), Load, Reliability • -IS-IS & OSPF – Cost, Bandwidth (Cisco’s implementation)

  28. Routing Protocols Metrics • Load balancing • This is the ability of a router to distribute packets among multiple same cost paths

  29. Administrative Distance of a Route • Purpose of a metric • It’s a calculated value used to determine the best path to a destination • Purpose of Administrative Distance • It’s a numeric value that specifies the preference of a particular route

  30. Administrative Distance of a Route • Identifying the Administrative Distance (AD) in a routing table • It is the first number in the brackets in the routing table

  31. Administrative Distance of a Route • Dynamic Routing Protocols

  32. Administrative Distance of a Route • Directly connected routes • Have a default AD of 0 • Static Routes • Administrative distance of a static route has a default value of 1

  33. Administrative Distance of a Route • Directly connected routes • -Immediately appear in the routing table as soon as the interface is configured

  34. Categories of Routing Protocols • Most routing algorithms can be classified into one of two categories: • distance vector • link-state • The distance vector routing approach determines the direction (vector) and distance to any link in the internetwork. • The link-state approach, also called shortest path first, recreates the exact topology of the entire internetwork.

  35. Distance VectorRouting Concepts

  36. Destination 192.16.1.0 192.16.5.0 192.16.7.0 Distance 1 1 2 Routing table contains the addresses of destinations and the distance of the way to this destination. 2 Hops 1 Hop 1 Hop Router B Router C Router D Router A Flow of routing information 192.16.7.0 192.16.1.0 192.16.5.0 Distance Vector Routing (DVR)

  37. Routing Tables Graphic

  38. Distance VectorTopology Changes

  39. Router Metric Components

  40. 192.16.3.0 192.16.2.0 192.16.6.0 192.16.4.0 192.16.7.0 192.16.1.0 192.16.5.0 0 192.16.2.0 L 192.16.4.0 0 L L 192.16.6.0 0 192.16.1.0 0 L 0 L 192.16.3.0 192.16.5.0 L 0 192.16.7.0 0 L 192.16.2.0 L 0 L 192.16.4.0 0 L 192.16.6.0 0 192.16.1.0 0 L 192.16.2.0 0 L 192.16.4.0 0 L 192.16.6.0 0 L Router D Router B Router C Router A 192.16.2.0 0 L 192.16.3.0 0 L 192.16.5.0 0 L 192.16.7.0 0 L 192.16.3.0 1 B 192.16.4.0 0 L 192.16.6.0 0 L 192.16.5.0 1 C 192.16.4.0 1 B 192.16.1.0 1 A 192.16.3.0 1 B 192.16.4.0 1 C 192.16.5.0 1 C 192.16.2.0 1 B 192.16.6.0 1 C 192.16.7.0 1 D L Locally connected Distance Vector Routing (DVR)

  41. 192.16.1.0 0 L 192.16.2.0 0 L 192.16.4.0 0 L 192.16.6.0 0 L 192.16.2.0 0 L 192.16.3.0 0 L 192.16.5.0 0 L 192.16.7.0 0 L 192.16.3.0 1 B 192.16.4.0 0 L 192.16.6.0 0 L 192.16.5.0 1 C 192.16.4.0 1 B 192.16.1.0 1 A 192.16.3.0 1 B 192.16.4.0 1 C 192.16.5.0 2 B 192.16.5.0 1 C 192.16.2.0 1 B 192.16.3.0 2 C 192.16.6.0 2 B 192.16.6.0 1 C 192.16.7.0 1 D 192.16.2.0 2 C 192.16.7.0 2 C 192.16.1.0 2 B 192.16.1.0 0 L 192.16.2.0 0 L 192.16.4.0 0 L 192.16.6.0 0 L 192.16.2.0 0 L 192.16.3.0 0 L 192.16.5.0 0 L 192.16.7.0 0 L 192.16.3.0 1 B 192.16.4.0 0 L 192.16.6.0 0 L 192.16.5.0 1 C 192.16.4.0 1 B 192.16.1.0 1 A 192.16.3.0 1 B 192.16.4.0 1 C 192.16.5.0 2 B 192.16.5.0 1 C 192.16.2.0 1 B 192.16.3.0 2 C 192.16.6.0 2 B 192.16.6.0 1 C 192.16.7.0 1 D 192.16.2.0 2 C 192.16.7.0 3 B 192.16.7.0 2 C 192.16.1.0 2 B 192.16.1.0 3 C Distance Vector Routing (DVR) Fig. 53 Distribution of routing information with distance vector routing protocol (cont.) (TI1332EU02TI_0004 The Network Layer, 71)

  42. Link State Routing protocol

  43. Link State Concepts

  44. Link State Topology Changes

  45. Link State Routing (LSR) SPF Router 1 Router 4 Router 2 Router 3 Routing Table LSP: „My links to R2 and R4 are up“ LSP: „My links to R1 and R3 are up. My link to R2 is down.“ LSP: „My links to R2 and R4 are up.“ LSP: „My links to R1 and R3 are up, my link to R4 is down.“ LSP....link state packet SPF... shortest path first

  46. Link State Concerns

  47. A B Router A Router C Router B Router D Router E C D B C A D D A E C B D C E E B A E Link State Routing (LSR) 1 4 2 2 1 4 Link State Database B - 2 C - 1 A - 2 D - 4 A - 1 D - 2 E - 4 C - 2 B - 4 E - 1 C - 4 D - 1 Router A Router B Router C Router D Router E

  48. Link State Routing Features • Link-state algorithms are also known as Dijkstras algorithm or as SPF (shortest path first) algorithms. • Link-state routing algorithms maintain a complex database of topology information. • The distance vector algorithm are also known as Bellman-Ford algorithms. They have nonspecific information about distant networks and no knowledge of distant routers. • A link-state routing algorithm maintains full knowledge of distant routers and how they interconnect. Link-state routing uses: • Link-state advertisements (LSAs) • A link-state advertisement (LSA) is a small packet of routing information • that is sent between routers. • Topological database • A topological database is a collection of information gathered from LSAs. • SPF algorithm • The shortest path first (SPF) algorithm is a calculation performed on the • database resulting in the SPF tree. • Routing tables – A list of the known paths and interfaces.

  49. Link State Routing

  50. Comparing Routing Methods

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