Software Defining Network

Question 1

Examples of Network management tasks

Answer 1

balancing traffic load
achieving security goals
satisfying business relationships

Question 2

Examples of Network Configuration Errors

Answer 2

1. Persistent oscillations can occur when routers can’t agree on a route to a destination.
2. Loops
3. Partitions occur when the network is split into two or more segments that are not connected.
4. Black holes (router will just drop the packet)

Question 3

The main goal of SDN

Answer 3

Change device-level configuration - centralize the network configuration to a logically centralized controller.

Question 4

Three things that SDN provide operators

Answer 4

1. Provides operators with network-wide views of both topology and traffic
2. the ability to satisfy network-level objectives, such as load balancing and security
3. allows an operator to write a control program that directly affects the data plane.

Question 5

Two functions of today’s routers

Answer 5

Data Plane: forward traffic

Control Plane: compute routing tables (state) to make decisions for data plane

Question 6

Defining features of SDN

Answer 6

1. Control plane (software program written in high-level language) runs in a logically centralized controller
2. Provide network view - control all of the routers in the network

Question 7

Advantages of SDN

Answer 7

1. easier debug and reason
2. easier coordination of behavior across network devices
3. easier evolution of network behavior

Question 8

Reasons for separating data and control plane

Answer 8

1. Independent evolution of data plane (network hardware) & control plane (software control)
2. Easier debug and reason
3. Separate vendor hardware from the control logic

Question 9

How does control/data separation make managing data center easier?

Answer 9

1. Monitor/control of routers from a central point

2. Migrating VMs without renumbering host address

Question 10

Challenges of SDN

Answer 10

Scalability: hundreds to thousands of switches
Consistency: ensure different replicas see the same view
Security/robustness: cope with failers

Question 11

Ways to cope with scalability challenges

Answer 11

1. eliminate redundant data structures
2. only perform control-plane operations for a limited number of operations
3. cache forwarding decisions in switches
4. run multiple controllers