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Exploring Unicast Routing Protocols: OSPF, BGP in Practice

Learn about OSPF and BGP routing protocols, how router tables are filled, and real-world applications. Understand multicast routing differences. Dive into Unicast vs. Multicast vs. Broadcasting scenarios.

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Exploring Unicast Routing Protocols: OSPF, BGP in Practice

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  1. Chapter 11 Unicast Routing Protocols (RIP, OSPF, BGP) (How the routers’ tables are filled in)

  2. Popular Unicast Routing protocols • RIP(already covered) – Routing Information Protocol – treats each network the same (assigns the same cost for each network) • OSPF – Open Shortest Path First protocol – assigns a cost for passing through a network based on the type of service required – routes through the network can have different cost – each router would have several tables • BGP – Border Gateway Protocol – is an exterior routing protocol that uses a policy that defines what paths should be chosen

  3. OSPF: Open Shortest Path First • Similar to RIP however, divide autonomous system into areas • Routers with in an area floods the area with routing info – router sends to all it’s neighbors and each neighbor sends to all it’s neighbors and etc.. • At the border of an area, special routers called area border routers are used to (1) summarize info about an area and (2) send info amongst areas • A special area called the backbone is used to tie together all of the areas – backbone is primary area and all other areas are secondary areas – backbone area uses backbone routers • Note: backbone router can also be an area border router • Each area has an ID (backbone’s Id is 0) Explain Current Real World Practices relating to this topic

  4. Recall OSPF: Open Shortest Path First • The OSPF is similar to RIP however, it allows the admin the ability to assign a cost or metric to each route. • The metric can be based on a type of service (ie . Min delay, max throughput, etc..) • For OSPF, a router will have multiple routing tables – one for each TOS • Unlike RIP, sharing or updating is done when there is a change (not periodically) • For OSPF, the objective is for the routers to contain the full picture or topology of the Internet – by having this, the router can figure out the “shortest path” or “least cost” route between itself and each network • To do this, the Internet is represented by a graph – set of edges and nodes

  5. Defining edges or connections/links Point-to-point link Virtual link Direct connection between two routers, no IP address needed Bi-directional Edge When link between two routers are broken, admin creates a new route across multiple routers Transient link Stub link Represents the network Connects to only one router – packets enter and leave through this same router

  6. Graphical representation of an internet

  7. OSPF uses Dijkstra’s Shortest Path Algorithm

  8. Dijkstra’s Algorithm Cont..

  9. Dijkstra’s Algorithm Continued At this point, we would have the least cost path from A to all other nodes Note: to find the least cost paths from E to all other nodes, Disjkstra’s algorithm has to run again

  10. Answer in Hyphen Format A-D A-D-N3 A-D-N3-F A-D-N3-F-N5 A-N1 A-N1-B A-N1-B-E A-N1-B-E-N4 A-N1-C A-N1-C-N2

  11. A re-occurring theme How do the OSPF packets travel across the network(s) ??????????????

  12. OSPF packets are encapsulated in IP datagrams.

  13. BGP: Border Gateway Protocol BPG is an inter-autonomous system routing protocol that makes use of path vector routing For BPG, each routing entry contains (1) destination network, (2) next router (hop) and (3) entirepath to reach destination Path is an ordered list of autonomous systems that the packet should travel through to make it to the destination

  14. Ch 12: Multicast Routing Lecture

  15. Put Your Unicast RoutingHAT on Lecture

  16. Recall Unicasting Vs Multicasting Vs Broadcasting Unicasting Case: • In unicast routing, the router forwards the received packet through only one of its interfaces. • Both the source and destination addresses are unicast addresses • One-to-One Relationship Lecture

  17. Multicasting Case Packet starts from source, S1, and goes to all destinations belonging to group, G1 • In multicast routing, the router may forward the received packet through several of its interfaces. • The source address is unicast and the destination address is a group address (Class D) • Group address define a set of Rx’s • One-to-Many Relationship • Actually, the packet is DUPLICATED at each router – only one copy travels in between any two routers Lecture

  18. Broadcasting Case • One-to-all case would cause traffic problems Lecture

  19. Multicasting versus multiple unicasting • Recall Multicasting • One packet start from source and is duplicated at each router • Only one copy of the packet travels in between any two routers • Packet has a single group address • Multiple Unicast Case • More than one copy of the packet starts from the source • Each copy of the packet has a different destination address • In this case, there could be multiple copies traveling between any two routers Multicast is more efficient than multiple unicast because in the unicast cast, some links will use more bandwidth in handling more packet copies. Also for the unicast case, there is more delay at the source due to packet duplication Lecture

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