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Routing Protocols

Routing Protocols. A router ‘knows’ only of networks attached to it directly – unless you configure a static route or use routing protocols Routing protocols share this information among immediate neighbors first, and then throughout the network

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Routing Protocols

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  1. Routing Protocols • A router ‘knows’ only of networks attached to it directly – unless you configure a static route or use routing protocols • Routing protocols share this information among immediate neighbors first, and then throughout the network • Routers do not calculate the entire path to a destination • They select the next hop leading to that destination • Rely on the next hop router to select a further hop that gets the packet closer to its destination • A router’s routing tables contains information about the networks directly connected to it, as well as information that the router has “learned” about more distant networks (sample of a routing table)

  2. Routing Protocols (cont.) • Important function of a router (layer 3): • Examine incoming data packets and make path selection based on information stored in their routing tables • Router evaluates the available paths to a destination to establish the best path for routing a packet. • Most routing protocols use the shortest and best path - but by different means.

  3. Static Routing • Characteristics of static routing: • administrators manually configure static routes • routes do not change, unless changed by the administrator • are useful in environments where there is a single link in or out of the networks (know as a stub network) • because there is only one link to get to the neighbor network, we conserve bandwidth not being used by routing protocols

  4. Static Routing Static route can be defined by: RouterA(config)# ip route <dest network> <subnet mask> < interface | next hop> 192.16.10.1 s0 Network 200.10.10.0/24 Router A Router B (Packets arriving at Router A with network 200.10.10.0 as their destination will be sent to the serial port of the next router – that is, the next hop) RouterA(config)# ip route 200.10.10.0 255.255.255.0 192.16.10.1 (The same thing can be accomplished by this: Packets arriving at Router A with network 200.10.10.0 as their destination will be sent out of Router A via Serial port 0) RouterA(config)# ip route 200.10.10.0 255.255.255.0 s0

  5. Static Routing 192.16.10.1 s0 Network 200.10.10.0 Router A Router B e0 195.10.10.0 net Static address command for network 195.10.10.0 to get to network 200.10.10.0 is: RouterA(config)# ip route 200.10.10.0 255.255.255.0 192.16.10.1 OR RouterA(config)# ip route 200.10.10.0 255.255.255.0 s0 Note that when the interface option is specified, it’s our interface ( RouterA - not the neighbor’s).

  6. Static Routing 192.16.10.1 s0 Network 200.10.10.0 Router A Router B RouterA(config)# ip route 200.10.10.0 255.255.255.0 192.16.10.1 RouterA(config)# show ip route The above example will have anadministrative distance of 1 in the routing table. RouterA(config)# ip route 200.10.10.0 255.255.255.0 s0 The above example will have anadministrative distance of 0 in the routing table.

  7. Static Routing 192.16.10.1 s0 Network 200.10.10.0 Router A Router B RouterA(config)# ip route 200.10.10.0 255.255.255.0 192.16.10.1 If the network 192.16.10.0 goes down for any reason, the static address on RouterA will beremoved from the routing table.

  8. Static Routing

  9. Default Route Gateway of last resort for routers that do not have a network entry in the routing table If router doesn’t know where to send a packet, it uses a default route: RouterA(config)# ip route 0.0.0.0 0.0.0.0 < interface | next hop> Packets going to any network for which I don’t have an entry in the routing table, just send them to the next hop 192.16.10.1 s0 Router A Internet RouterA(config)# ip route 0.0.0.0 0.0.0.0 192.16.10.1 OR RouterA(config)# ip route 0.0.0.0 0.0.0.0 s0

  10. DefaultRoute on non-directly connected networks

  11. Default/Static Route • To verify a static route or default route use the commands: • show running-config • Or • show ip route • To test a static route or default route use the commands: • ping • Or • traceroute

  12. Examine the Show ip route command [Administrative distance / Hop count]

  13. Default Administrative Distances

  14. Routed Vs. Routing Protocols • Routed vs. Routing: • Routed protocols are protocols are protocols used to carry the data across the networks – like those in the IP protocol (such as Telnet) and Novel lIPX • Routing protocols route routed protocols through a network. (Routers use routing protocols to talk to each other about networks & paths. • Dynamically advertise and learn routes, determine which routes are available and which are the most efficient routes to a destination) • IGRP (Interior Gateway Routing Protocol) • EIGRP ( Enhanced IGRP) • BGP (Border Gateway Protocol) • OSPF (Open Shortest Path First) • APPN (Advanced Peer-to-Peer Networking) • IS-IS (Intermediate System-to Intermediate System) • RIP (Routing Information Protocol)

  15. Autonomous Systems An autonomous system (AS) is a collection of networks under acommonadministration. The American Registry of Internet Numbers (ARIN) assigns an identifying number to each AS. AS is a16 bit number. Some routing protocols such as IGRP, EIGRP requires AS for their configurations.

  16. Routing Protocols When complex networks have multiple interconnections, static routes are not a practical solution – they can’t react to changes in the topology When all routers in an internetwork are operating with the same knowledge of the routes in a network is said to haveconverged. Fast convergence is desirable because it reduces the period of time in which routers would continue to make incorrect routing decisions. In routers that use dynamic routing protocols, it is important to have fast convergence because routers could make incorrect forwarding decisions until the network has fully converged.

  17. Routing Protocols (cont.)

  18. Routing Protocols (cont.) • Routing protocols are divided into 2 classes: • interior - used for routing information within networks that are under a common network administrator • RIP • IGRP • OSPF • EIGRP • exterior - used for routing information between networks that do not share a common administrator. • EGP (exterior gateway protocol) • BGP

  19. Classes of Routing Protocols • Classes of Routing Protocols • distance-vector- determines the direction & distance • IGRP • RIP • link-state(also called shortest path first) re-creates the exact topology of the entire network. • OSPF • IS-IS

  20. Distance Vector Routing Protocols Distance vector routing algorithms passperiodiccopies of a routing table from router to router. These regular updates are based on the routing algorithm know as ‘Bellman-Ford’ algorithm. However distance vector algorithms do not allow a router to know the exact topology of an internetwork as each router only sees its neighbor routers.

  21. Distance Vector Routing Protocols Neighbor to neighbor ONLY

  22. Distance Vector Routing Protocols

  23. Distance Vector Routing Protocols Routing table updates take placeperiodically. Router to router (neighbor tells neighbor) Distance vector – each router sends its entire routing table to neighbor table

  24. Link-state Routing Protocol • Link-state algorithms are also known as Dijkstras algorithm or SPF (shortest path first) algorithm. • Link-state routing algorithms maintain a complex database of topology information. It maintainsfull knowledgeof distant routers and how they are interconnected. • Link-state routing uses: • Link-state Advertisements (LSAs) • Small packets of routing info that are sent between routers • Topological database • SPF algorithm • Routing tables

  25. Link-state Routing Protocol • Link-state makes anupdate onlywhen there is atopology change. • Link-state concerns itself with: • processor overhead • memory requirements • bandwidth consumption • After the initial flood, it passes small event-triggered updates to all other routers

  26. Routing Metrics A responsibility of a Routing Protocol is to build routing tables to determine optimal routing paths They need to have a way to measure (metrics) which routes are preferred when there are multiple paths to a destination Different routing protocols use different metrics Hop count: number of routing devices the packet needs to travel to reach the destination network Bandwidth: cumulative bandwidth of the links to the destination measured in kilobits per second Delay: length of time (in microseconds) a packet takes from source to destination Reliability: consistency of the links and paths toward the destination based on the interfaces’ error rates Load: cumulative amount of congestion of the links in the direction of the destination

  27. Routing Metrics (cont.) Hop count: number of routing devices the packet needs to travel to reach the destination network - counts router hops Bandwidth: cumulative bandwidth of the links to the destination measured in kilobits per second Delay: length of time (in microseconds) a packet takes from source to destination Reliability: consistency of the links and paths toward the destination based on the interfaces’ error rates Load: cumulative amount of congestion of the links in the direction of the destination MTU: maximum frame size that is allowed to cross the links to the destination Cost: arbitrary number typically based on the bandwidth of the link

  28. 192.168.1.5601-00-A5-C3-26-6B 192.168.1.5634-7E-33-12-C9-20 192.168.1.566A-5F-0D-09-8B-AA 192.168.1.56BC-48-03-8F-FF-AA The Routing Process • The protocol address (IP) always remains the same. • The physical address (MAC) changes at each hop. 192.168.1.56

  29. RIP Routing Protocol • Characteristics of RIP are: • distance vector • metric is hop count • if the hop count is greater than 15, the packet is discarded • is updated every30 seconds • For RIP, each router that it has to go through to get to a network is considered a hop count. That is, if you have to go through 2 routers to get to a network, then the hop count is 2. • If the network is on the next router, then the hop count is 0. (That is a directly connected serial port.)

  30. IGRP Routing Protocol • IGRP: • must be assigned an AS(autonomous system number - 16 bit number) • Cisco proprietary • distance-vector • metrics • delay • bandwidth (1200 bps - 10 Gbps) • reliability (1-224) (higher the number, more reliable) • load (1-244) (higher the number, more it is under load) • sendsupdates every 90 seconds • maximum hop count is 255 (default 100)

  31. OSPF Routing Protocol • Characteristics of OSPF are: • link-state routing protocol • open standard • uses the SPF algorithm to calculate the lowest cost to a destination • routing updates are flooded as topology changes occur.

  32. EIGRP Routing Protocol • Characteristics of EIGRP are: • distance-vector • Cisco proprietary • uses load balancing • uses a combination of distance vector & link-state features • use Diffused Update Algorithm (DUAL) to calculate the shortest path • updates broadcast every90seconds

  33. BGP Routing Protocol • Characteristics of BGP are: • distance vector exterior routing protocol • used between ISP and clients • used to route internet traffic between autonomous systems

  34. Configure Routing Protocols RouterA#config t RouterA(config)# router<routing protocol>[AS number] RouterA(config-router)# network<networks on the routers interfaces> Example: RouterA(config)# router rip RouterA(config-router)# network 192.16.10.0 Example: RouterA(config)# router igrp 100 RouterA(config-router)# network 192.16.10.0 ‘advertises’ networks directly connected to it

  35. Configure RIP Routing Protocol 210.45.20.0 net s0 192.10.10.0 net s1 e0 172.120.0.0 net RouterA# config t RouterA(config)# router rip RouterA(config-router)# network 192.10.10.0 RouterA(config-router)# network 172.120.0.0 RouterA(config-router)# network 210.45.20.0

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