9-Software Defined Networking

Question 1

What is network management

Answer 1

Process of configuring network to achieve a variety of tasks

Question 2

Network configurations achieve a variety of tasks:

Answer 2

• Load Balance
• Security
• Business Relationships

Question 3

Configuration mistakes can lead to

Answer 3

1) Oscillation - Routers cant agree on a route to a destination
2) Loops - Packets get stuck between two or more routers and never make it to the destination
3) Partitions - The network is split into two or more segments that are not connected.
4) “Black Holes” - Packets reach a router that does not know what to do with the packet and drops instead of sending to destination

Question 4

Why is configuration hard?

SDN changes this

Answer 4

1) Defining Correctness is hard
2) Interactions between protocols -> unpredictability
3) Operators make mistakes

Question 5

SDN provides operators 3 things

Answer 5

1) Network wide views
-topology and traffic
2) Network-level objectives
-load balance and security
3) Direct control
0>direct manipulation of data plane

Question 6

Routers should

Answer 6

1) Forward packets

2) Collect measurements (statistics and topology info)

Question 7

Routers should not

Answer 7

Compute routes

Question 8

SDN

Answer 8

Removes routing from routers

Question 9

What is SDN?

Answer 9

1) Logically centralized control

2) Network-wide control

Question 10

Today: control and data planes run on routers

Answer 10

Data plane: Forward traffic

Control plane: compute routing tables

Question 11

First in 2004 was the RCP (resource control protocol)

Answer 11

Worked on BGP only

Question 12

2004: RCP
2005: 4D
2008: Openflow

Answer 12

History

Question 13

Advantages of SDN

Answer 13

1) Coordination
2) Easy to evolve
3) Reasoning

All because of separate control plane

Question 14

Control plane:

Answer 14

Software Program (i.e. Python, C…)
Logic that controls forwarding behavior
examples: routing protocols, configuration for network middleboxes

Question 15

Data plane:

Answer 15

Programmable hardware (controlled by the control plane)
Forward traffic according to control plane logic
examples: forwarding, switching

Question 16

SDN Application

Answer 16

Data Centers *
Backbone Networks *
Enterprise Networks *
IXPs
Home Networks

This course will focus on 1st 3 *

Question 17

Examples of control plane operations?

Answer 17

1) Computing a forwarding path that satisfies a high level policy
2) Computing a shortest path routing tree
3) Authenticating a users device based on MAC Addresses

Question 18

Why separate data and control plane?

Answer 18

1) independent evolution -> software & hardware can evolve independently
2) Control from high-level program -> allows operators to debug and check behavior easily

Question 19

Why separate data and control plane?

Answer 19

1) Data centers: VM migration
2) Routing: More control over decision logic
3) Enterprise networks: Security
4) Research networks: Coexistense with production networks

Question 20

Why separate data and control plane? Quiz

Answer 20

1) Independent evolution of data and control plane
2) Separating vendor hardware from control logic
3) Easier reasoning about network behavior

Question 21

Data centers

Answer 21

SDN helps with VM migrations

Question 22

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

Answer 22

1) Monitoring/control of routers from a central point

2) Migrating VMs without renumbering hosts addresses

Question 23

Why separate data and control plane?

Answer 23

Backbone security

Goal: filter the attack traffic

Question 24

Challenges for SDN

Answer 24

1) Scalability: Hundreds to thousands of switches
2) Consistency: ensuring different replicas to see same view
3) Security/Robustness: Failure or compromise?

Question 25

Ways to cope with scalability challenges?

Answer 25

1) Eliminate redundant data structures
2) Only perform control-plane operations for a limited # of ops
3) Cache forwarding decisions in switches
4) Run multiple controllers

Question 26

Different SDN controllers

Answer 26

NOX, RYU, FLOODLIGHT (This lesson)

PYRETIC, FRENETIC (Programming SDN)

Question 27

NOX

Answer 27

*First generation Openflow controller ->open-source, stable, widely used
Two flavors:
-Classic: C++, PYTHON
-New NOX: C++ only, fast, clean

Question 28

NOX Architecture

Answer 28

Components: 1) Switches
2) Network-attached servers
Abstraction: Switch control
Control: Flow granularity

Question 29

What is a Flow?

Answer 29

(header: counter, actions)
header= 10 tuple
counter
actions = forward, drop, sending to controller

Question 30

NOX: Programmatic Interface

Answer 30

Performance is good but requires an understandings of low-level openflow commands and C++

Question 31

When to use POX???

Answer 31

Class project or University research but NOT in a large internet datacenter because it does not perform as well as other controllers.

Question 32

RYU

Answer 32

Python, OF 1.0,1.2,1.3, Open Stack

Question 33

Floodlight

Answer 33

Java, OF 1.0, fork from “beacon”, Good documentation and performance… but has a steep learning curve.

Question 34

NOX

Answer 34

C++, OF 1.0, good performance, slow programming/debugging hard

Question 35

POX

Answer 35

Python, OF 1.0, performance ok… not the best, easy to program

Question 36

POX Algoritm for Switch

Answer 36

See Udacity video #17

Question 37

Modifying forwarding behavior is easy!

Answer 37

Switching:
Flow switching:
Firewall:

Question 38

Caching

Customizing control is easy

Answer 38

1) Packets only reach controller if no flow table entry at the switch
2) When controller decides an action on a packet, installs in switch
3) Decision/flow table entry is cached

Question 39

You can turn a switch into a firewall

Answer 39

in less than 40 lines of Python code