CST 311 Intro to Computer Networks Module 6: Network Layer: The Control Plane

 1.0 Learning Objectives for the Week

• Gain an Understanding of the principles behind the network control plane
• Learn traditional routing algorithms and where there are used.
• Learn about the SDN control plane
• Learn about Internet Control Message Protocol (ICMP) and its use for diagnostics and alerting.
• Investigate a basic SDN controller using Mininet and Wireshark.
• Investigate IPv6 addressing using Mininet and Wireshark.
• Implement and test a multi-threaded client-server chat program.

Chapter 5.1 Introduction

• Per router control (OSPF and BGP)  Routing algorithm will run in each and every router that can do both forwarding and routing functions. Routers have components that can communicate with one another to compute values for it's forwarding table. Used in OSPF and BGP protocols. 
• Logically Centralized Control (SDN) A Centralized Controller will compute and distribute a forwarding table that will be used by each router. The Control Agent(CA) do not directly interact with one another or take part in computing the forwarding table. SDN is an example of this.  

Chapter 5.2 Routing Algorithms 

• Routing Algorithms It's job is to determine a good path from sender to receiver which has the least cost. This is one of the top 10 list of important networking concepts. 
• Graph(Nodes(N), Edge(E)) This is used to formulate routing problems.  The cost factor is represented in the Edge which may be length of the link, link speed, or cost of the link. 
• Least Cost Path  The path between source and destination that has the least cost.
• Shortest Path  The path with the smallest number of links between source and destination.
• Centralized Routing Algorithm/Link State Algorithm Computes the LEAST COST PATH using complete global knowledge about the network. This algo takes into account the connection between each link and how much it costs. 
• Link State (LS) Algorithms These are algorithms that takes into account the global state information such as the centralized routing algorithm. 
• Decentralized Routing Algorithm/Distance Vector Algorithm Calculating the least cost path without full knowledge of the costs of network links but instead using knowledge of its own costs and links directly attached to it. But then it will gain more knowledge as it moves down the link. 
• Static Routing Algorithms Routers change slowly over time which may result in a human interrupting to manually edit a link cost.
• Dynamic Routing Algorithm Routes change accordingly to traffic loads or change in topology but may experience more problems including routing loops and route oscillations. 
• Load Sensitive Algorithm Costs of links will vary depending on how congestive the network is. ARPAnet.
• Load-Insensitive Algorithms Costs of links don't depend on how congested the current network is. This is what today's routing algorithm uses such as RIP, OSPF, and BGP

Chapter 5.2.1 The Link State (LS) Routing Algorithm 

• Link State Broadcast Algorithm LS Algorithm needs to know all of the link costs for the paths taken so it sends out a link state packes from nodes to other nodes that contain its own and neighboring link costs. 
• Dijkstra's Algorithm Computers least cost path from one node. This algo is iterative and after the Nth iteration, the least cost path are known to N destination nodes and among the least cost paths to all destinations nodes, these N paths will have the N smallest cost. 

Chapter 5.2.2 The Distance-Vector (DV) Routing Algorithm 

• The Distance Vector Algorithm This algorithm is iterative, asynchronous, and distributed. 
• Distributed : Each nodes receives information from its directly attached neighbors, performs a calculation, then sends the results back to its neighbors. 
• Iterative : Continues until no more information is exchanged
• Asynchronous : Doesn't need all of the nodes to operate at the same time.
  
• Routing Loop Occurs when packets are bouncing back and forth until the forwarding table changes.
  
• Poisoned Reverse If z routes through y to get to x, then z will tell y that its distance to x is infinity, which will cause y to never attempt to route to x via z. 

Chapter 5.3 Intra-AS Routing in the Internet: OSPF

• Autonomous Systems Organizing routers into groups that are under the same administrative control. 
• Intra-Autonomous System Routing Protocol Routing algorithms that are running with an autonomous system. 
• Open Shortest Path First (OSPF) Used mostly for intra-AS routing on the internet. This link state protocol uses flooding of link-state info and a Dijkstra's least-cost path algorithm.

Chapter 5.4 Routing Among the ISPs : BGP

• Inter-Autonomous System Routing Protocol Helps determine the route the packet follows when dealing with routing a packet under the same AS such as the BGP. 
• BGP Provides routers two things: 1). Obtain prefix reachability information from neighboring ASs and 2) Determine the "best" routes to the prefixes 
• Gateway Router A router on the edge of an AS that connects to one or more routers in other ASs.
• Internal Router A router that connects only to a host and routers within its own AS. 

1.1 Weekly Review

Overall this week has been very hectic and busy. I learned more about the network layer, finished up the group project, and did all the assignments. Networking is a very difficult subject and an 8 week course is not ideal since the amount of breadth and depth covered is a lot. I enjoyed the programming assignments alot better than the classwork for this class since I know I won't be going into networking or IT.