Transcript SDN-TAUx

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
constant innovation
Applications:
Internet Protocols:
routing, congestion
stagnant! control, naming, …
(TCP/IP, BGP, DNS, OSPF, ECMP,…)
Technologies:
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
Control plane:
distributed algorithms
track topology changes, compute
routes, install forwarding rules
Traditional Computer Networks
Management plane:
human time scale
collect measurements and configure
the equipment
New Paradigm:
Software Defined Networking (SDN)
logically-centralized control
smart,
slow
API to the data plane
(e.g., OpenFlow)
dumb,
fast
switches
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A Helpful Analogy
Mainframes
AppAppAppAppAppAppAppAppAppAppApp
Specialized
Applications
Specialized
Operating
System
Specialized
Hardware
vertically integrated
closed, proprietary
slow innovation
small industry
Open Interface
Windows
(OS)
or
Linux
or
Open Interface
Microprocessor
horizontal
open interfaces
rapid innovation
huge industry
Mac
OS
Routers/Switches
AppAppAppAppAppAppAppAppAppAppApp
Specialized
Features
Specialized
Control
Plane
Specialized
Hardware
vertically integrated
closed, proprietary
slow innovation
Open Interface
Control
Control
Control
or
or
Plane
Plane
Plane
Open Interface
Merchant
Switching Chips
horizontal
open interfaces
rapid innovation
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How SDN works
The OpenFlow protocol
OpenFlow Switching
OpenFlow Switch specification
OpenFlow Switch
Secure
sw Channel
hw
Flow
Table
PC
Controller
Controller: Programmability
Controller Application
Network OS
events from switches
topology changes,
traffic statistics,
arriving packets
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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
Rule
Action
Stats
Packet + byte counters
1. Forward packet to port(s)
2. Encapsulate and forward to controller
3. Drop packet
4. Send to normal processing pipeline
Switch
Port
+ mask
MAC
src
MAC
dst
Eth
type
VLAN
ID
IP
Src
IP
Dst
IP
Prot
TCP
sport
TCP
dport
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
src=0*
src=1*
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In-depth Example: Simple Repeater
Controller
1
2
Switch
• Simple Network Repeater
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– forward packets received on port 1 out 2 and vice versa
Simple Repeater
Controller (POX) (Pseudo)-Program
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
1
2
Switch
Flow Table
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Priority
Pattern
Action
Counters
DEFAULT
IN_PORT:1
OUTPUT:2
(0,0)
DEFAULT
IN_PORT:2
OUTPUT:1
(0,0)
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 (?)
access
control
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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?
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Challenges
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”
packets
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Distributed Controller
Controller
Application
For scalability and
reliability
Controller
Application
Partition and replicate state
Network OS
Network OS
… and: where to put the
controller(s)?
Taking into account latency,
resiliency, load balancing...
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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
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Programming Abstractions
• Controller APIs are low-level
– Thin veneer on the underlying hardware
• Need better languages
– Composition of modules
Controller
– Managing concurrency
– Querying network state
– Network-wide abstractions
• Example:
– http://www.frenetic-lang.org/
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Switches
MiniNet
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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
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MiniNet
• Not only for teaching purposes!
• Used for the development and testing
of networks
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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
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How to Solve this Problem?
Idea: Distribute the rules among all
switches such that each packet goes
through all rules along its path.
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Palette: Step I
Split the large (TCAM) table into smaller tables
– identify each smaller table with a unique colour
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Palette: Step II
Assign at most a single colour to each switch s.t.
every packet-forwarding path is a “rainbow path”
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/tr1205_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
Packet
i
X
d
forwarding path? No!
Routing: Data vs. Control Plane
• 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!
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
• Outgoing edge is a function of
-
incoming edge
set of live edges
d
fid: Ei x P(Ei) -> Ei
i
Resilient Forwarding
• Forwarding is t-resilient iff for any
(at most) t edge failures:
– existence of path from i to d ⇒ loopfree forwarding from to d
• Perfect resilience ≣ t →∞
Thm: Can always protect against
one failure
Big Gap!
Thm: Cannot always provide perfect
resilience
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
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– in both research and industry
Thank You