software defined networkingmsagiv/courses/rsdn/sdn-tau.pdf · –requires smarter approaches than...
TRANSCRIPT
Software Defined Networking
What is it, how does it work, and what is it good for?
Many slides stolen from Jennifer Rexford, Nick McKeown, Scott Shenker, Teemu Koponen, Yotam
Harchol and David Hay
Agenda
• What is Software Defined Networking (SDN)?
• What is OpenFlow? How does it work?
• Challenges en route to SDN
• Research directions
What is SDN?
The Internet: A Remarkable Story
• Tremendous success
– from research experiment to global infrastructure
• Enables innovation in applications
– Web, P2P, VoIP, social networks, virtual worlds
• But, the Internet’s infrastructure remained fairly stagnant for decades
The Internet’s Landscape
Applications:
Internet Protocols:
routing, congestion control, naming, …
(TCP/IP, BGP, DNS, OSPF, ECMP,…)
Technologies:
constant innovation
stagnant!
constant innovation
Why Can’t We Innovate?
• 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
Impacts performance, security, reliability, cost…
Networks are Hard 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
Traditional Computer Networks
Data plane: packet
streaming
forward, filter, buffer, mark, rate-limit, and measure packets
Traditional Computer Networks
track topology changes, compute routes, install forwarding rules
Control plane: distributed algorithms
Traditional Computer Networks
collect measurements and configure the equipment
Management plane: human time scale
New Paradigm: Software Defined Networking (SDN)
API to the data plane (e.g., OpenFlow)
logically-centralized control
switches
smart, slow
dumb, fast
A Helpful Analogy
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vertically integrated closed, proprietary
slow innovation small industry
Specialized Operating System
Specialized Hardware
App App App App App App App App App App App
Specialized Applications
horizontal open interfaces rapid innovation huge industry
Microprocessor
Open Interface
Linux Mac OS
Windows (OS) or or
Open Interface
Mainframes
vertically integrated closed, proprietary
slow innovation
App App App App App App App App App App App
horizontal open interfaces rapid innovation
Control Plane
Control Plane
Control Plane
or or
Open Interface
Specialized Control Plane
Specialized Hardware
Specialized Features
Merchant Switching Chips
Open Interface
Routers/Switches
How SDN works
The OpenFlow protocol
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OpenFlow Switch
Flow Table
Secure Channel
PC
hw
sw
OpenFlow Switch specification
OpenFlow Switching
Controller
Controller: Programmability
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Network OS
Controller Application
events from switches topology changes, traffic statistics, arriving packets
commands to switches (un)install rules, query statistics,
send packets
Reactive vs. Proactive
• Reactive SDN: switches send (first) packets to controller, then controller programs switch's flow table to handle rest of the flow
– Problem: source of DoS on controller (packet-in event)
• Proactive SDN: Controller programs the switches proactively, according to its own knowledge of the network
– Requires smarter approaches than just reacting to network events (global knowledge, discovery, updates…)
Flow Table Entry at Switch “Type 0” OpenFlow Switch
Switch Port
MAC src
MAC dst
Eth type
VLAN ID
IP Src
IP Dst
IP Prot
TCP sport
TCP dport
Rule Action Stats
1. Forward packet to port(s) 2. Encapsulate and forward to controller
3. Drop packet 4. Send to normal processing pipeline
+ mask
Packet + byte counters
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
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
OpenFlow
• Definition in progress
• Additional actions
rewrite headers
map to queue/class
encrypt
• More flexible header
allow arbitrary matching of first few bytes
• Support multiple controllers
load-balancing and reliability
Example OpenFlow Applications
• Dynamic access control
• Seamless mobility/migration
• Server load balancing
• Network virtualization
• Using multiple wireless access points
• Energy-efficient networking
• Adaptive traffic monitoring
• Denial-of-Service attack detection
See http://www.openflow.org/videos/
E.g.: Dynamic Access Control
• Inspect first packet of a connection
• Consult the access control policy
• Install rules to block or route traffic
E.g.: Seamless Mobility/Migration
• See host send traffic at new location
• Modify rules to reroute the traffic
E.g.: Server Load Balancing
• Pre-install load-balancing policy
• Split traffic based on source IP
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src=0*
src=1*
In-depth Example: Simple Repeater
• Simple Network Repeater
– forward packets received on port 1 out 2 and vice versa 26
1 2
Controller
Switch
Simple Repeater
Priority Pattern Action Counters
DEFAULT IN_PORT:1 OUTPUT:2 (0,0)
DEFAULT IN_PORT:2 OUTPUT:1 (0,0)
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def handle_packetIn(packet): out_port = 2 if packet.in_port == 2: out_port = 1 flow_mod = ofp_flow_mod() flow_mod.match = ofp_match() flow_mod.match.in_port = \ packet.in_port action = ofp_action_output() action.out_port = out_port flow_mod.action = [ action ] flow_mod.buffer_id = \ packet.buffer_id send(flow_mod)
Controller (POX) (Pseudo)-Program
Flow Table
1 2
Controller
Switch
OpenFlow in the Wild
• Open Networking Foundation
– 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, POX, …
• Network deployments
– Campuses, research backbone networks
– Commercial deployments (e.g., Google backbone)
But… Heterogeneous Switches
• Number of packet-handling rules (TCAM/memory limits)
• Different OpenFlow version support
• Range of matches and actions (not all matches and actions are mandatory in the protocol)
• Multi-stage pipeline of packet processing (allowed but not defined in the standard)
• Vendor-specific features
• Offload some control-plane functionality (?)
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access control
MAC look-up
IP look-up
SDN or OpenFlow?
• OpenFlow is not being adapted as-is
• Major vendors either completely discard OpenFlow or use a massively changed variant
• Doing that requires having the ability to change the protocol on both sides (controller + switch)
• Is OpenFlow dead?
30
Challenges
31
Controller Delay and Overhead
• Controller is much slower the the switch
• Processing packets leads to delay and overhead
• Need to keep most packets in the “fast path”
32
packets
Distributed Controller
33
Network OS
Controller Application
Network OS
Controller Application
For scalability and reliability
Partition and replicate state
… and: where to put the controller(s)?
Taking into account latency, resiliency, load balancing...
Testing and Debugging
• OpenFlow makes programming possible
– Network-wide view at controller
– Direct control over data plane
• Plenty of room for bugs
– Still a complex, distributed system
• Need for testing techniques
– Controller applications
– Controller and switches
– Rules installed in the switches 34
Programming Abstractions
• Controller APIs are low-level
– Thin veneer on the underlying hardware
• Need better languages
– Composition of modules
– Managing concurrency
– Querying network state
– Network-wide abstractions
• Example:
– http://www.frenetic-lang.org/
35
Controller
Switches
MiniNet
36
MiniNet
• Creates scalable SDN (up to hundreds of nodes) using OpenFlow, on a single PC
• Allows to quickly create, interact with and customize a SDN prototype with complex topologies, and can be used to emulate real networks – all on your PC
• Can work with any kind of OpenFlow controller
• Takes seconds to install
• Easy to program
• Of course, is an open source project
37
MiniNet
• Not only for teaching purposes!
• Used for the development and testing of networks
38
Innovating with SDN
Dealing with Large Tables
Palette: Distributing Tables in Software Defined Networks
Y. Kanizo, D. Hay and I. Keslassy
Access Control in SDN
• Consider the following network.
– Table at each ingress point
Ingress points hold (too) large tables
41
How to Solve this Problem?
Idea: Distribute the rules among all switches such that each packet goes through all rules along its path.
42
Palette: Step I
Split the large (TCAM) table into smaller tables
– identify each smaller table with a unique colour
43
Assign at most a single colour to each switch s.t. every packet-forwarding path is a “rainbow path”
Palette: Step II
Algorithmic Challenges
• Maximizing the number of colours (smaller tables), k
• Splitting the large (TCAM) table into k smaller tables
– so as to minimize the size of the largest table
• http://webee.technion.ac.il/~isaac/p/tr12-05_palette.pdf
Rethinking (Routing) Protocols
On the Resilience of Routing Tables:
J. Feigenbaum, P. B. Godfrey, A. Panda, M. Schapira, S. Shenker, and A. Singla
Motivation
d
Motivation
d
Routes computed by, say, shortest paths routing alg
Motivation
i d X
forwarding path? No!
Pack
et
• Routing is a control plane operation
– slow (ms – s)
• Packet forwarding is a data plane operation
– fast (μs)
• Today’s routing protocols
1. establish connectivity
2. optimize routes (= shortest paths)
• failure ⇒ re-convergence ⇒ dropped packets!
Routing: Data vs. Control Plane
How to Solve this Problem?
Idea: Push (only!) connectivity to the data plane
– immediately react to failures
– optimize routes on a longer time scale
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Forwarding Model
• Packet for node d arrives at node i
i d
• Outgoing edge is a function of
- set of live edges
- incoming edge
fid: Ei x P(Ei) -> Ei
• Forwarding is t-resilient iff for any (at most) t edge failures:
– existence of path from i to d ⇒ loop-free forwarding from to d
• Perfect resilience ≣ t →∞
Resilient Forwarding
Big Gap!
Thm: Cannot always provide perfect resilience
Thm: Can always protect against one failure
What Next?
• Conditions for k-resilience?
– restricted failure models?
• Resilience for specific families of graphs?
• Randomized forwarding rules?
• ... ?
Full paper available online as YALE/DCS/TR1454 See also [Liu-Panda-Singla-Godfrey-S-Shenker, NSDI 2013]
Conclusion
• SDN is revolutionizing networking
• Rethinking networking
– open interfaces to the data plane
– separation of control and data
– leveraging techniques from distributed systems
• Significant momentum, many challenges
– in both research and industry 56
Thank You