9-Software Defined Networking Flashcards by Tony Mack

What is network management

Process of configuring network to achieve a variety of tasks

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Network configurations achieve a variety of tasks:

Load Balance
Security
Business Relationships

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Configuration mistakes can lead to

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

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Why is configuration hard?

SDN changes this

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

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SDN provides operators 3 things

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

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Routers should

1) Forward packets

2) Collect measurements (statistics and topology info)

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Routers should not

Compute routes

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SDN

Removes routing from routers

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What is SDN?

1) Logically centralized control

2) Network-wide control

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Today: control and data planes run on routers

Data plane: Forward traffic

Control plane: compute routing tables

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First in 2004 was the RCP (resource control protocol)

Worked on BGP only

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2004: RCP
2005: 4D
2008: Openflow

History

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Advantages of SDN

1) Coordination
2) Easy to evolve
3) Reasoning

All because of separate control plane

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Control plane:

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

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Data plane:

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

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SDN Application

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

This course will focus on 1st 3 *

Examples of control plane operations?

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

Why separate data and control plane?

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

Why separate data and control plane?

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

Why separate data and control plane? Quiz

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

Data centers

SDN helps with VM migrations

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

1) Monitoring/control of routers from a central point

2) Migrating VMs without renumbering hosts addresses

Why separate data and control plane?

Backbone security

Goal: filter the attack traffic

Challenges for SDN

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

Ways to cope with scalability challenges?

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

Different SDN controllers

NOX, RYU, FLOODLIGHT (This lesson) | PYRETIC, FRENETIC (Programming SDN)

NOX

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

NOX Architecture

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

What is a Flow?

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

NOX: Programmatic Interface

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

When to use POX???

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

RYU

Python, OF 1.0,1.2,1.3, Open Stack

Floodlight

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

NOX

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

POX

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

POX Algoritm for Switch

See Udacity video #17

Modifying forwarding behavior is easy!

Switching: Flow switching: Firewall:

Caching | Customizing control is easy

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

You can turn a switch into a firewall

in less than 40 lines of Python code