ACO330 Quiz 6

Consider Dijkstra's link-state routing algorithm that is computing a least-cost path from node a to other nodes b, c, d, e, f. Which statements are true. - 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. - The values computed in the vector D(v), the currently known least cost of a path from a to any node v, will never increase following an iteration. - In the initialization step, the initial cost from 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 known least cost of a path from 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. - The values computed in the vector D(v), the currently known least cost of a path from a to any node v, will never increase following an iteration. - In the initialization step, the initial cost from 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.

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)." - Driven more by routing policy than end-end routing performance - intra-AS routing - inter-AS routing - inter-domain routing - BGP - OSPF - Driven more by performance than by routing policy - intra-domain routing

- intra-AS routing - OSPF - Driven more by performance than by routing policy - intra-domain routing

Network-control applications - (c) - (a) - (b)

(a)

SDN Controller (network operating system) - (c) - (a) - (b)

(b)

SDN-controlled switches - (c) - (a) - (b)

(c)

Suppose a provider network only wants to carry traffic to/from its customer networks (i.e., to provide no transit service), and customer networks only want to carry traffic to/from itself. Consider the figure below. To implement this policy, to which of the following networks would network C advertise the path Cy? - B - x - w - A

- B - x - A

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

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

Which of the following statements correctly identify the differences between routing and forwarding. Select one or more statements. - Forwarding refers to moving packets from a router's input to appropriate router output, and is implemented in the data plane. - Routing refers to moving packets from a router's input to appropriate router output, and is implemented in the data plane. - Routing refers to determining the route taken by packets from source to destination, and is implemented in the control plane. - Forwarding refers to moving packets from a router's input to appropriate router output, and is implemented in the control plane. - Routing refers to determining the route taken by packets from source to destination, and is implemented in the data plane.

- Forwarding refers to moving packets from a router's input to appropriate router output, and is implemented in the data plane. - Routing refers to determining the route taken by packets from source to destination, and is implemented in the control plane.

Which of the statements below about ICMP are true? - ICMP messages are carried directly in IP datagrams rather than as payload in UDP or TCP segments. - ICMP communicates information between hosts and routers by marking bits in the IP header. - ICMP messages are carried in UDP segments using port number 86. - 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 payload in UDP or TCP segments. - 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.

Which of the functions below belong in the controller layer labeled "Interface, abstractions for network control apps"? Check all below that apply. - Flow tables - Intent - Host information - Network graph - Statistics - Switch information - Link-state information - OpenFlow protocol

- Intent - Network graph

Check the one or more of the following statements about the OSPF protocol that are true. - OSPF is an intra-domain routing protocol. - OSPF is an interdomain routing protocol. - OSPF implements hierarchical routing - OSFP uses a Dijkstra-like algorithm to implement least cost path 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 implements hierarchical routing - OSFP uses a Dijkstra-like algorithm to implement least cost path routing.

Which of the functions below belong in the controller layer labeled "Communication to/from controlled device"? Check all below that apply. - Statistics - OpenFlow protocol - Link-state information - Network graph - Flow tables - Intent - Switch information - Host information

- OpenFlow protocol

Interdomain routing. - Forwarding packets between two physically connected interfaces in a common subnetwork. - Routing among routers within same AS ("network"). - Routing among different ASes ("networks"). - Forwarding packets between two interfaces in different but adjacent subnetworks.

- Routing among different ASes ("networks").

Which of the functions below belong in the controller layer labeled "Network-wide distributed, robust state management"? Check all below that apply. - Statistics - Intent - Host information - Switch information - Network graph - Link-state information - OpenFlow protocol - Flow tables

- Statistics - Host information - Switch information - Link-state information - Flow tables

Consider the graph shown below and the use of Dijkstra's algorithm to compute a least cost path from a to all destinations. Suppose that nodes b and d have already been added to N'. What is the path cost to the next node to be added to N' (refer to the text for an explanation of notation). - 7 - 5 - 4 - 6

4

Software-defined networking (SDN). - A (typically) remote controller gathers information from routers, and then computes and installs the forwarding tables in routers. - Individual routing algorithm components - with a component operating in each and every router - interact with each other in the control plane. The individual routing algorithm component executing in a given router computes the local fowarding table fir that router. - The network operator installs forwarding tables using the Simple Network Management Protocols (SNMP).

A (typically) remote controller gathers information from routers, and then computes and installs the forwarding tables in routers.

Centralized, global routing. - Routes change slowly over time. - Routing changes quickly over time. - All routers have complete topology, and link cost information. - An iterative process of computation, exchange of information with neighbors. Routers may initially only know link costs to directly-attached neighbors.

All routers have complete topology, and link cost information.

Decentralized routing - Routes change slowly over time. - Routing changes quickly over time. - All routers have complete topology, and link cost information. - An iterative process of computation, exchange of information with neighbors. Routers may initially only know link costs to directly-attached neighbors.

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

Which one of the following protocols is/are example of a distributed routing algorithm - OSPF - BGP - OSPF & BGP

BGP

As part of hierarchical routing, hot-potato routing does the following: - Determines the number of ASes in the shortest AS path from router to destination. - Chooses the gateway that has the smallest cost. - Labels suspicious packets as "hot". - Provides information to a router about the existence of external networks.

Chooses the gateway that has the smallest cost.

Which one of the statements below is not true about network layer per-router controller? - Each router has a routing component that communicates with the routing components in other routers to compute the values for its forwarding table. - Each router implements its own control and data planes. - Data plane is implemented in a centralized component

Data plane is implemented in a centralized component

True or false: Every autonomous system must use the same intra-autonomous system routing algorithm.

False

True or false: In a distance-vector routing algorithm, each node has a map of the entire network and determines the shortest path from itself to all other nodes in the network.

False

True or false: In the BGP routing algorithm, each AS advertises to its neighbors its estimates of the shortest distances from the AS to all possible destination ASs.

False

True or false: It is necessary that every autonomous system use the same intra-AS routing algorithm.

False

True or false: OSPF uses BGP for routing among areas.

False

How does router 2d learn of the path AS3, X to destination network X? - From x via eBGP. - From 2c via iBGP. - From 3a via eBGP. - From 2c via eBGP. - From 3a via iBGP.

From 2c via iBGP.

How does router 2c learn of the path AS3, X to destination network X? - From x via eBGP. - From 2c via iBGP. - From 3a via eBGP. - From 2c via eBGP. - From 3a via iBGP.

From 3a via eBGP.

Per-router control plane: - A (typically) remote controller gathers information from routers, and then computes and installs the forwarding tables in routers. - Individual routing algorithm components - with a component operating in each and every router - interact with each other in the control plane. The individual routing algorithm component executing in a given router computes the local fowarding table fir that router. - The network operator installs forwarding tables using the Simple Network Management Protocols (SNMP).

Individual routing algorithm components - with a component operating in each and every router - interact with each other in the control plane. The individual routing algorithm component executing in a given router computes the local fowarding table fir that router.

Again, suppose a provider network only wants to carry traffic to/from its customer networks (i.e., to provide no transit service), and customer networks only want to carry traffic to/from itself. Suppose C has advertised path Cy to x. To implement this policy, to which of the following networks would network x advertise the path xCy? - B - A - None of these other networks - C - w

None of these other networks

Which one of the statements below is not true about OSPF intra-AS routing - Routers broadcast their routing information only to directly attached neighbors. - Each router constructs a complete topological map of the entire AS. - Routers run Dijkstra's shortest-path algorithm to determine its least-cost paths to all other nodes in the same AS

Routers broadcast their routing information only to directly attached neighbors.

Static routing. - Routes change slowly over time. - Routing changes quickly over time. - All routers have complete topology, and link cost information. - An iterative process of computation, exchange of information with neighbors. Routers may initially only know link costs to directly-attached neighbors.

Routes change slowly over time.

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

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

Intradomain routing - Forwarding packets between two physically connected interfaces in a common subnetwork. - Routing among routers within same AS ("network"). - Routing among different ASes ("networks"). - Forwarding packets between two interfaces in different but adjacent subnetworks.

Routing among routers within same AS ("network").

Dynamic routing. - Routes change slowly over time. - Routing changes quickly over time. - All routers have complete topology, and link cost information. - An iterative process of computation, exchange of information with neighbors. Routers may initially only know link costs to directly-attached neighbors.

Routing changes quickly over time.

Which of the following statements best describes the purpose of the SNMP protocol: - The SNMP protocol specifies the actions a network manager should take in response to a specific set of network fault conditions. - The SNMP protocol is a tool for gathering data about network conditions and executing remote actions at remote managed devices - The SNMP protocol is used by the network manager to provision resources, such as bandwidth, server capacity and other computational/communication resources needed to meet the mission-specific needs of an enterprise

The SNMP protocol is a tool for gathering data about network conditions and executing remote actions at remote managed devices

Which one of the statements below is not true about centralized routing algorithms? - The algorithm needs to have the complete knowledge of the connectivity between all nodes and all links' costs - The actual calculation always runs at one site - The actual calculation may be replicated in the routing component of the routers

The actual calculation always runs at one site

True or false: Data plane is always implemented in each router

True

The link-state algorithm in Section 4.5 has the following properties: - after the kth iteration, the least-cost paths are known to k nodes - it requires the source node to know the costs between every pair of adjacent nodes in the graph - it determines the shortest path from the source node to all other nodes - all of the above

all of the above

Consider the graph shown below and the use of Dijkstra's algorithm to compute a least cost path from a to all destinations. Suppose that nodes b and d have already been added to N'. What is the next node to be added to N' (refer to the text for an explanation of notation). - e - c - f

e

In routing among AS's, which of the following issues dominants: number of AS's traversed - geographical distance between AS's - current congestion levels in the AS's - policy - right answer feedback:

policy

The ICMP protocol - runs on top of UDP - runs on top of TCP - runs directly on top of IP - none of the above

runs directly on top of IP

Again, suppose a provider network only wants to carry traffic to/from its customer networks (i.e., to provide no transit service), and customer networks only want to carry traffic to/from itself. Suppose C has advertised path Cy to A. To implement this policy, to which of the following networks would network A advertise the path ACy? - B - C - w - x

w