TODAY’S TENTATIVE AGENDA 5pm-515pm 1. Return graded project 1 2. Lecture 14: I know you are anxious and want to only focus on taking the exam – so I will briefly cover OSPF and post the details 515pm-630pm 3. Exam Dr. Clincy

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

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 Dr. Clincy

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 Dr. Clincy

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 Dr. Clincy

You Can Now Start Exam 2 Dr. Clincy

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 Dr. Clincy

Graphical representation of an internet Dr. Clincy

OSPF uses Dijkstra’s Shortest Path Algorithm Dr. Clincy

Dijkstra’s Algorithm Cont.. Dr. Clincy

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 Dr. Clincy

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 Dr. Clincy

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

OSPF packets are encapsulated in IP datagrams. Dr. Clincy

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) entire path to reach destination Path is an ordered list of autonomous systems that the packet should travel through to make it to the destination Dr. Clincy