Reasoning about Software Defined Networks

Mooly Sagivmsagiv@acm.org03-640-7606

Tel Aviv UniversityThursday 16-18 (Physics 105)Monday 14-16 Schrieber 317Adviser: Michael Shapira

Hebrew University

http://www.cs.tau.ac.il/~msagiv/courses/rsdn.html

Content

• Motivation (Due to Jennifer Rexford)• A simple example• A more interesting example• What is “reasoning”• Seminar requirements• Tentative schedule

The Internet: A Remarkable Story

• Tremendous success– From research experiment

to global infrastructure• Brilliance of under-specifying– Network: best-effort packet delivery– Hosts: arbitrary applications

• Enables innovation in applications– Web, P2P, VoIP, social networks, virtual worlds

• But, change is easy only at the edge… 3

Inside the ‘Net: A Different Story…• Closed equipment– Software bundled with hardware– Vendor-specific interfaces

• Over specified– Slow protocol standardization

• Few people can innovate– Equipment vendors write the code– Long delays to introduce new features

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Impacts performance, security, reliability, cost…

Do We Need Innovation Inside?

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Many boxes (routers, switches, firewalls, …), with different interfaces.

How Hard are Networks to Manage?

• Operating a network is expensive– More than half the cost of a network– Yet, operator error causes most outages

• Buggy software in the equipment– Routers with 20+ million lines of code– Cascading failures, vulnerabilities, etc.

• The network is “in the way”– Especially a problem in data centers– … and home networks

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Creating Foundation for Networking

• A domain, not a discipline– Alphabet soup of protocols– Header formats, bit twiddling– Preoccupation with artifacts

• From practice, to principles– Intellectual foundation for networking– Identify the key abstractions– … and support them efficiently

• To build networks worthy of society’s trust7

Rethinking the “Division of Labor”

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Traditional Computer Networks

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Data plane:Packet streaming

Forward, filter, buffer, mark, rate-limit, and measure packets

Traditional Computer Networks

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Track topology changes, compute routes, install forwarding rules

Control plane:Distributed algorithms

Traditional Computer Networks

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Collect measurements and configure the equipment

Management plane: Human time scale

Shortest-Path Routing

• Management: set the link weights• Control: compute shortest paths• Data: forward packets to next hop

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Shortest-Path Routing

• Management: set the link weights• Control: compute shortest paths• Data: forward packets to next hop

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Inverting the Control Plane

• Traffic engineering– Change link weights– … to induce the paths– … that alleviate congestion

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Avoiding Transient Anomalies

• Distributed protocol– Temporary disagreement among the nodes– … leaves packets stuck in loops– Even though the change was planned!

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Death to the Control Plane!

• Simpler management– No need to “invert” control-plane operations

• Faster pace of innovation– Less dependence on vendors and standards

• Easier interoperability– Compatibility only in “wire” protocols

• Simpler, cheaper equipment– Minimal software

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Software Defined Networking (SDN)

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API to the data plane(e.g., OpenFlow)

Logically-centralized control

Switches

Smart,slow

Dumb,fast

OpenFlow Networks

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Data-Plane: Simple Packet Handling

• Simple packet-handling rules– Pattern: match packet header bits– Actions: drop, forward, modify, send to controller – Priority: disambiguate overlapping patterns– Counters: #bytes and #packets

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1. src=1.2.*.*, dest=3.4.5.* drop 2. src = *.*.*.*, dest=3.4.* forward(2)3. src=10.1.2.3, dest=*.*.*.* send to controller

Controller: Programmability

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Network OS

App #1 App #2 App #3

Events from switchesTopology changes,Traffic statistics,Arriving packets

Commands to switches(Un)install rules,Query statistics,Send packets

OpenFlow in the Wild• Open Networking Foundation– Creating Software Defined Networking standards– Google, Facebook, Microsoft, Yahoo, Verizon, Deutsche Telekom,

and many other companies• Commercial OpenFlow switches– HP, NEC, Quanta, Dell, IBM, Juniper, …

• Network operating systems– NOX, Beacon, Floodlight, Nettle, ONIX, POX, Frenetic

• Network deployments– Eight campuses, and two research backbone networks– Commercial deployments

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Dynamic Access Control• Inspect first packet of each connection• Consult the access control policy• Install rules to block or route traffic

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Seamless Mobility/Migration• See host sending traffic at new

location• Modify rules to reroute the traffic

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Example Applications

• Dynamic access control• Seamless mobility/migration• Server load balancing• Using multiple wireless access points• Energy-efficient networking• Adaptive traffic monitoring• Denial-of-Service attack detection• Network virtualization

24See http://www.openflow.org/videos/

Challenges of Programming Software Defined Networks

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Programming OpenFlow Networks

• OpenFlow makes programming possible– Network-wide view at controller– Direct control over data plane

• The APIs do not make it easy– Low level of abstraction

• Challenges– Composition– Concurrency– Correctness– Testing

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Controller

Switches

A Simple example: Firewall

• A switch connected to two kind of hosts– Trusted hosts via port 1– Untrusted hosts via port 2

• Trusted hosts can freely send packets to untrusted hosts

• An unstrusted host can only send to a trusted destination which previously sent messages to this host

Firewall

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Firewall Controller Pseudo-code

rel trusted(SW, HO) packetIn(s, p, 1) # packets from trusted hosts send(s, p, 2) # forward the packet to untrusted hosts trusted.insert(s, p.dst) # insert the target of p into trusted controller memory ft.insert(s, p, 1, 2) # insert a per-flow rule to forward future packets

packetIn(s, p, 2) -> # packets from untrusted hosts if trusted(s, p.src) then { send(s, p, 1) # forward the packet to trusted hosts ft.insert (s, p, 2, 1) # insert a per-flow rule to forward future packets }

Firewall Controller Pseudo-code(2)

packetIn(s, p, 1) # packets from trusted hosts send(s, p, 2) # forward the packet to untrusted hosts ft.insert(s, src:p.src, 1, 2) # insert a general rule to forward future packets ft.insert(s, dst:p.dst, 2, 1) # allow future packets from 2

A Learning Switch• Ttwo hosts (A & B) • An OpenFlow switch with 3 ports• Host A is connected to port 1• and Host B is connected to port 2• Gradually install forwarding rules• Update upon relocation

Host A

Switch1

2Host B

‘A’ sends a message to ‘B’

Host A

Switch1

2Host B

TCP syn dst=B

Forward to the Controller

Host A

Switch1

2Host B

TCP syn dst=B

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send TCP syn dst=B on port 2

send TCP syn dst=B on port 3

learn that A is connected via port 1

‘B’ sends a message to ‘A’

Host A

Switch1

2Host BTCP ack dst=A

Forward to the Controller

Host A

Switch1

2Host B

TCP ack dst=A

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send TCP ack dst=A on port 1

learn that B is connected via port 2

Install a rule to forward packets from B to A on port 1

‘A’ sends another message to ‘B’

Host A

Switch1

2Host B

dst=B

Forward to the Controller

Host A

Switch1

2Host B

dst=B

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Send dst=B on port 2

Install a rule to forward packets from A to B to port 2

Learning Switch Pseudo-code

rel connected (SW, PR, HO)PacketIn(s, p, e) -> connect.insert (s, e, p.src) if connect(s, o, p.dst) then { send (s, p, o) ft.insert(s, p, e, o) } else foreach o in {1, 2, 3} – p # Flood send (s, p, o)

Reasoning about Programs

• Debugging• Testing– Model checking

• Programming language support– Abstraction– Composition– Ease of use

• Program verification– Abstraction

Seminar Benefits

• A cool topic• Reasoning• Critically read an article• Learn to present an article

Seminar Requirements

• Compilers• Read an article (2 weeks)• Prepare presentation (1 week)• Participate in lectures

Tentative Schedule

October 24 Michael Shapira

Introduction to SDN

October 31 Mooly Sagiv Introduction to Program Reasoning

November 7 ? ?

November 14 ? ?