Programming SDN

Question 1

Openflow consistence problem

Answer 1

1. update may disrupt packets along an end to end path. 2. Packets from the same flow might be disrupted.

Question 2

Examples fo state openflow may read

Answer 2

failures, topology changes, security events, etc.

Question 3

Compute Policy

Answer 3

decide forwarding behavior

Question 4

Write Policy

Answer 4

Save the policy back to the swtiches

Question 5

What makes openflow programming difficult

Answer 5

rules are simple match action rules

Question 6

size problem

Answer 6

Limits the number of rules. Cannot install all possible patterns

Question 7

Solution to the size problem

Answer 7

Dynamically unfold rules as traffic arrives. Programmer specifies “GroupBy (srcip)”. Runtime dynamically adds rules as traffic arrives.

Question 8

Problems when reading state

Answer 8

Extra unexpected events might arrive. 1st packet go to control then decision is made. Solution 1. Programmer specifies “limit(1)”. Runtime hides extra events

Question 9

3 approaches to help guaranty consistence when reading state

Answer 9

Predicates, unfolding, suppression

Question 10

Writing policy: Avoiding Disruption

Answer 10

Need atomic updates of the entire configuration.

Question 11

Solution to writing disruption issue

Answer 11

2 phase commit version numbers in packets

Question 12

Optimization for 2 phase commit.

Answer 12

Only apply mechanism on switches that involve affected versions of traffic or topology i.e. Keeping the old and new state on routers and switches

Question 13

What is network virtualization?

Answer 13

Abstraction of physical network. Multiple logical networks share physical substrate

Question 14

Why use network virtualization

Answer 14

To work around “Ossification” of internet architecture.

Question 15

Ossification

Answer 15

A tendency toward or state of being molded into a rigid, conventional, sterile or unimaginative condition.

Question 16

What does network virtualization enable

Answer 16

evolution by letting multiple architectures exist in parallel

Question 17

Promise of network virtualization

Answer 17

Rapid innovation (software speed), New forms of network control, Potentially simpler programming

Question 18

SDN vs Network Virtualization

Answer 18

SDN: Separate data and control NV: separate logical and physical

Question 19

Characteristics of network virtualization

Answer 19

Allowing multiple tenants to share underlying physical infrastructure. Separating logical and physical networks

Question 20

Design goals for network vertiualization

Answer 20

Flexible, Manageable, scalable, secure, programmable, able to support different technologies

Question 21

Nodes of Virtual Network

Answer 21

Must be virtualized

Question 22

Edges

Answer 22

Tunnels. Encapsulate the ethernet frame in an ip packet. Decapsulate when virtual host is reached. Openvswitch.org

Question 23

Is mininet a virtual network or sdn

Answer 23

Virtual Network

Question 24

How do virtual networks facilitate flexible, agile, development?

Answer 24

Rapid innovation, Vendor independence, scale

Question 25

Solution to openflow programming difficulties

Answer 25

Northbound api

Question 26

Northbound api?

Answer 26

Api that allows communication with high level components

Question 27

Southbound api?

Answer 27

api that allows communication with low level components

Question 28

Frenetic

Answer 28

sql like query language

Question 29

Ways to compose policies

Answer 29

Parallel: Perform both policies operations simultaneously (e.g. Counting fowarding). Sequential: Perform one operation then the next.

Question 30

Pyretic features

Answer 30

Network policy as function. Boolean predicates (predicates on packets). Virtual packet header fields. Policy Composition.

Question 31

Dynamic Policies

Answer 31

Timeseries of static policies Current value: self.policy. 1. Set a default policy 2. register callback that updates policy.