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Chapter 21

Chapter 21. Routing Protocols. Routing. Intradomain Routing Interdomain Routing Autonomous System Distance Vector Routing Protocol Link State Routing Protocol Path Vector Routing Protocol. Autonomous System (AS) A group of networks & routers under the authority of common administration

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Chapter 21

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  1. Chapter 21 Routing Protocols

  2. Routing Intradomain Routing Interdomain Routing Autonomous System Distance Vector Routing Protocol Link State Routing Protocol Path Vector Routing Protocol

  3. Autonomous System (AS) A group of networks & routers under the authority of common administration Intradomain Routing Protocol Routing inside an Autonomous system Interdomain Routing Protocol Routing b/w Autonomous systems Routing cont…

  4. Distance Vector Routing Protocol The routing table is shared with the neighbor router(s) Can not be used in large networks The size of the N/W, in each direction, can not exceed 15 hops Examples are RIP and IGRP Routing cont…

  5. Link State Routing Protocol information about adjacencies (neighborship) sent to all routers only when there is a change Examples are OSPF and IS-IS Routing cont…

  6. OSPF is designed for large, scalable networks. allows dividing a large internetwork into smaller areas. OSPF

  7. Link - physical and electrical connection between two network devices. Link-state - status of a link between two routers. information about router's interface and its relationship to neighboring routers. Cost - value assigned to a link (based on speed of the network connection). Area - collection of networks and routers (has same area identification). Each router in an area, called an internal router, has the same link-state information. OSPF Terminology

  8. Designated Router (DR) - a router elected to represent all the routers in that network. Backup Designated Router (BDR) - becomes the DR, if original DR fails. Adjacencies database - listing of all neighbors to which a router has established communication. Link-state database(topological database) - information about all other routers in the network. shows the network topology. All routers in an area have identical link-state databases. OSPF Terminology cont…

  9. 5 types of ospf packets. 1 - Hello. 2 - DBD – database description packets. 3 - Link-state requests. 4 - Link-state updates (LSUs). 5 - Link-state acknowledgements. OSPF Packet Format

  10. OSPF Operation

  11. Done using the Hello protocol. establish virtual point-to-point links, adjacencies. ensure bi-directional communication between neighbors before exchanging link-state information. Hello packets are multi-cast Establishing Adjacencies

  12. 1. Router A first comes up - OSPF in down state. Router A sends Hello packet with its information. 2. All enabled OSPF routers receive the Hello packet and store info locally (Init state). 3. Routers send unicast reply Hello packet back to Router A with their own information. 4. From replies Router A adds all neighbor routers to its own database (two-way state). Now, all routers that have learned about each other establish bi-directional communication. Hello Protocol exchange process

  13. 5. Neighbor routers select the DR and BDR. (before routers can begin exchanging complete link-state information). 6. Neighboring routers determine master/slave relationship, exchange LSAs, and establish full adjacency. 7. Periodically (10 seconds by default), Hello packets ("keepalive" updates) are exchanged to ensure communication is still working. Hello Protocol exchange process (2)

  14. Help reduce routing update traffic Act as a central point of contact. Each router establishes adjacency with DR/BDR. sends LSAs only to DR/BDR. DR forwards LSAs to all other routers in network. Manage link-state synchronization Ensure all routers have same link-state information about the internetwork. BDR becomes DR, only if the DR fails. DR and BDR

  15. DR - router with highest priority. BDR - second highest priority. Priority 0 cannot become DR or BDR. If priorities are same, the higher Router ID is elected. No new election if another router is added. If DR fails, BDR becomes DR, and new BDR is elected. Electing DR and BDR

  16. After DR/BDR election, routers enters Exstart state. Route Discovery

  17. OSPF Configuration

  18. show ip ospf interface Verifies interface is configured – Router ID, DR & BDR, timer intervals, neighbors. show ip ospf # times SPF algorithm executed, link state update interval. show ip ospf neighbors List of neighbors, their priorities and states. show ip ospf database Displays contents of topological database. OSPF Commands

  19. Interdomain Routing Protocol One node, in each autonomous system, functions on behalf of the entire AS The node is called speaker node (for discussion) The speaker node in an AS creates routing table and advertises it to speaker node in the neighboring ASs Example is BGP (Border Gateway Protocol) Path Vector Routing Protocol

  20. Thank You Questions???

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