Computer Networks: Control Plane

Software Defined Networking (SDN)

A (typically) remote controller computes and install forwarding tables in routers.

Centralized, global routing

All routers have complete topology, and link cost information.

Decentralized routing

An interactive process of computation, exchange of information with neighbors. Routers may initially only know link costs to directly-attached neighbors.

Consider the OSPF routing protocol. Which of the following characteristics are associated with OSPF (as opposed to BGP)? Finds a least cost from source to destination Is an intra-domain routing protocol Policy, rather than performance (e.g., least cost path), determines path that used Floods link state control information Is an inter-domain routing protocol

Finds a least cost from source to destination Is an intra-domain routing protocol Floods link state control information

Per-router control plane

Individual routing algorithm components in each and every router interact in the control plane

Check the one or more of the following statements about the OSPF protocol that are true. OSPF implements hierarchical routing The Open Shortest Path First (OSPF) Internet routing protocol implements a Bellman-Ford distance-vector routing algorithm OSPF is an intra-domain routing protocol OSPF is an interdomain routing protocol OSFP uses a Dijkstra-like algorithm to implements least cost path routing

OSPF implements hierarchical routing OSPF is an intra-domain routing protocol OSFP uses a Dijkstra-like algorithm to implements least cost path routing

Static routing

Routes change slowly over time

Interdomain routing

Routing among different ASes ("networks")

Intradomain routing

Routing among routers within same AS ("network")

Dynamic routing

Routing changes quickly over time

Consider Dijstra's link-state routing algorithm that is computing a least-cost path from node a to other nodes b, c, d, e, f. Which of the following statements is true. The values computed in the D(v), the currently known least cost of a path form a to any node v, will always decrease following an iteration. Suppose nodes b, c, and d are in the set N'. These nodes will remain in N' for the rest of the algorithm, since the least-cost paths from a to b, c, and d are known. In the initialization step, the initial cost form a to each of these destinations is initialized to either the cost of a link directly connecting a to a direct neighbor, or infinity otherwise. The values computed in the vector D(v), the currently know least cost of a path from a to any node v, will never increase following an iteration. Following the initialization step, if nodes b and c are directly connected to a, then the least cost path to b and c will never change from this initial cost.

Suppose nodes b, c, and d are in the set N'. These nodes will remain in N' for the rest of the algorithm, since the least-cost paths from a to b, c, and d are known. In the initialization step, the initial cost form a to each of these destinations is initialized to either the cost of a link directly connecting a to a direct neighbor, or infinity otherwise. The values computed in the vector D(v), the currently know least cost of a path from a to any node v, will never increase following an iteration.

Which of the following statements about ICMP are true? The TTL-expired message type in ICMP is used by the traceroute program. ICMP is used by hosts and routers to communicate network-level information ICMP messages are carried directly in IP datagrams rather than as payloads in UDP or TCP segments ICMP messages are carried in UDP segments using port number 86. ICMP communicates information between hosts and routers by making bits in the IP header

The TTL-expired message type in ICMP is used by the traceroute program. ICMP is used by hosts and routers to communicate network-level information ICMP messages are carried directly in IP datagrams rather than as payloads in UDP or TCP segments

Among the following protocols, terminology or considerations, indicate those that are associated with "routing within a single network (typically owned and operated by one organization). a. Intra-domain routing b. inter-domain routing c. BGP d. Driven more by performance than by routing routing policy e. OSPF f. Driven more by routing policy than end-end routing performance g. Inter-AS routing h. Intra-AS routing

a. Intra-domain routing d. Driven more by performance than by routing routing policy e. OSPF h. Intra-AS routing

What is the definition of a "good" path for a routing protocol? Choose the best answer. a. A path that has little or no congestion b. A high bandwidth path c. A low delay path d. A path that has a minimum number of hops e. Routing algorithms typically work with abstract link weights that could represent any of, or combinations of, all of the other answers.

e. Routing algorithms typically work with abstract link weights that could represent any of, or combinations of, all of the other answers.

Routing

refers to determining the route taken by packets form source to destination, and is implemented in the control plane.

Forwarding

refers to moving packets form a router's input to appropriate router output, and is implemented in the data plane.