CST311 - Week 37

This week we were assigned to read Chapter 5 - The Network Layer: Control Plane in the textbook. This chapter covered the control plane which controls how datagrams are forwarded among routers on the path from source to destination. The control plane uses routing algorithms to determine the best paths to forward datagrams. We delved into two main algorithms: the link-state (LS) routing algorithm and the distance-vector (DV) algorithm. The LS algorithm determines the least-cost path using global knowledge of the network, as each node gives the least-cost path from itself to its neighbors to all nodes in the network. The DV algorithm, on the other hand, is decentralized and gives the least-cost path from itself to all nodes only to its immediate neighbors and keeps updating due to any changes. An autonomous system, AS, is a group of routers that are under the control of the same network administration. OSPF, Open Shortest Path First, is using for intra-AS routing. BGP, Border Gateway Protocol is used for inter-AS routing. Each subnet obtains a prefix and BGP allows subnets to advertise and make their prefixes known to the whole internet. BGP also allows routers to calculate the best routes to prefixes, using BGP attributes such as AS-PATH and NEXT-HOP. Route Selection algorithms are determined based on local preference value, shortest AS-PATH, closest NEXT-HOP router, and then BGP identifiers (in this order). Thus routing policy is a major component as it sets the local preference value of a route. The control plane has 3 layers: communication layer, network-wide state-management layer, and interface to network-control application layer. For example, the OpenFlow protocol allows for communication between the controller and SDN-controlled switch in the form of messages such as modify-State and port-status. Lastly, the chapter ended off discussing the Internet Control Message Protocol, ICMP, with which routers and hosts communicate network-layer information to each other, typically error messages.

This week we also completed two labs. Lab 9 Mininet OpenFlow first creates a topology that does not have an SDN controller and then we modified the topology to include an SDN controller and looked at OpenFlow packets between the controller and switch on Wireshark. Lab 10 IPv6 works with IPv6 addresses. Lastly, we submitted programming assignment #3, in which we wrote TCP client and server code to allow computers to communicate with each other with the use of sockets.