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High-Level Abstractions for Programming Software Defined Networks. Jennifer Rexford Princeton University http:// www.cs.princeton.edu /~ jrex. Joint with Nate Foster, David Walker, Arjun Guha , Rob Harrison, Chris Monsanto, Joshua Reich, Mark Reitblatt , Cole Schlesinger. - PowerPoint PPT Presentation
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High-Level Abstractions for Programming Software Defined
Networks
Joint with Nate Foster, David Walker, Arjun Guha, Rob Harrison, Chris Monsanto, Joshua Reich, Mark Reitblatt, Cole Schlesinger
Jennifer RexfordPrinceton University
http://www.cs.princeton.edu/~jrex
2
Software Defined Networks
3
decouple control and data planes
Software Defined Networks
4
decouple control and data planesby providing open standard API
Software Defined Networks
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(Logically) Centralized ControllerController Platform
6
Protocols ApplicationsController PlatformController Application
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Payoff
• Cheaper equipment• Faster innovation• Easier management
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But How Should We Program SDNs?
Controller Platform
Controller ApplicationNetwork-wide visibility and control
Direct control via open interface
Today’s controller APIs are tied to the underlying hardware
OpenFlow Networks
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Data Plane: 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
Control Plane: Programmability
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Events from switchesTopology changes,Traffic statistics,Arriving packets
Commands to switches(Un)install rules,Query statistics,Send packets
Controller Platform
Controller Application
E.g.: Server Load Balancing• Pre-install load-balancing policy• Split traffic based on source IP
src=0*
src=1*
Seamless Mobility/Migration• See host sending traffic at new location• Modify rules to reroute the traffic
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Programming Abstractions for Software Defined Networks
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Network Control Loop
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Readstate
OpenFlowSwitches
Writepolicy
Compute Policy
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Reading State
SQL-Like Query Language
Reading State: Multiple Rules• Traffic counters
– Each rule counts bytes and packets– Controller can poll the counters
• Multiple rules– E.g., Web server traffic except for source 1.2.3.4
• Solution: predicates– E.g., (srcip != 1.2.3.4) && (srcport == 80)– Run-time system translates into switch patterns
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1. srcip = 1.2.3.4, srcport = 802. srcport = 80
Reading State: Unfolding Rules• Limited number of rules
– Switches have limited space for rules– Cannot install all possible patterns
• Must add new rules as traffic arrives– E.g., histogram of traffic by IP address– … packet arrives from source 5.6.7.8
• Solution: dynamic unfolding– Programmer specifies GroupBy(srcip)– Run-time system dynamically adds rules
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1. srcip = 1.2.3.4 1. srcip = 1.2.3.42. srcip = 5.6.7.8
Reading: Extra Unexpected Events
• Common programming idiom– First packet goes to the controller– Controller application installs rules
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packets
Reading: Extra Unexpected Events
• More packets arrive before rules installed?– Multiple packets reach the controller
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packets
Reading: Extra Unexpected Events
• Solution: suppress extra events– Programmer specifies “Limit(1)”– Run-time system hides the extra events
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packets
not seen byapplication
Frenetic SQL-Like Query Language
• Get what you ask for– Nothing more, nothing less
• SQL-like query language– Familiar abstraction– Returns a stream– Intuitive cost model
• Minimize controller overhead– Filter using high-level patterns– Limit the # of values returned – Aggregate by #/size of packets
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Select(bytes) *Where(in:2 & srcport:80) *GroupBy([dstmac]) *Every(60)
Select(packets) *GroupBy([srcmac]) *
SplitWhen([inport]) *Limit(1)
Learning Host Location
Traffic Monitoring
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Computing Policy
Parallel and Sequential Composition
Abstract Topology Views
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Combining Many Networking Tasks
Controller Platform
Monitor + Route + FW + LB
Monolithic application
Hard to program, test, debug, reuse, port, …
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Modular Controller Applications
Controller Platform
LBRoute
Monitor FW
Easier to program, test, and debugGreater reusability and portability
A module for each task
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Beyond Multi-Tenancy
Controller Platform
Slice 1
Slice 2
Slice n
... Each module controls a different portion of the traffic
Relatively easy to partition rule space, link bandwidth, and network events across modules
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Modules Affect the Same Traffic
Controller Platform
LBRoute
Monitor FW
How to combine modules into a complete application?
Each module partially specifies the handling of the traffic
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Parallel Composition [ICFP’11, POPL’12]
Controller Platform
Route on dest
prefix
Monitor on source
IP+
dstip = 1.2/16 fwd(1)dstip = 3.4.5/24 fwd(2)
srcip = 5.6.7.8 countsrcip = 5.6.7.9 count
srcip = 5.6.7.8, dstip = 1.2/16 fwd(1), countsrcip = 5.6.7.8, dstip = 3.4.5/24 fwd(2), countsrcip = 5.6.7.9, dstip = 1.2/16 fwd(1), countsrcip = 5.6.7.9, dstip = 3.4.5/24 fwd(2), count
• Spread client traffic over server replicas– Public IP address for the service– Split traffic based on client IP– Rewrite the server IP address
• Then, route to the replica
Example: Server Load Balancer
clients
1.2.3.4
load balancerserver replicas
10.0.0.1
10.0.0.2
10.0.0.3
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Sequential Composition [NSDI’13]
Controller Platform
RoutingLoad Balancer >>
dstip = 10.0.0.1 fwd(1)dstip = 10.0.0.2 fwd(2)
srcip = 0*, dstip=1.2.3.4 dstip=10.0.0.1srcip = 1*, dstip=1.2.3.4 dstip=10.0.0.2
srcip = 0*, dstip = 1.2.3.4 dstip = 10.0.0.1, fwd(1)srcip = 1*, dstip = 1.2.3.4 dstip = 10.0.0.2, fwd(2)
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Dividing the Traffic Over Modules
• Predicates– Specify which traffic traverses which
modules– Based on input port and packet-header
fieldsRouting
Load Balancer
Monitor
Routing
dstport != 80
dstport = 80 >>
+
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High-Level Architecture
Controller Platform
M1 M2 M3 Composition Spec
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Partially Specifying Functionality
• A module should not specify everything– Leave some flexibility to other modules– Avoid tying the module to a specific
setting• Example: load balancer plus routing
– Load balancer spreads traffic over replicas
– … without regard to the network pathsLoad
Balancer Routing>>Avoid custom interfaces between the modules
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Abstract Topology Views [NSDI’13]• Present abstract topology to the
module– Implicitly encodes the constraints – Looks just like a normal network– Prevents the module from overstepping
34Real network Abstract view
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Separation of Concerns• Hide irrelevant details
– Load balancer doesn’t see the internal topology or any routing changes
Routing view Load-balancer view
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High-Level Architecture
Controller Platform
View Definitions M1 M2 M3 Composition
Spec
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Supporting Topology Views• Virtual ports
– (V, 1): [(P1,2)]– (V, 2): [(P2, 5)]
• Simple firewall policy– in=1 out=2
• Virtual headers– Push virtual ports– Route on these ports– From (P1,2) to (P2,5)
V1 2
firewall
routing
P1 P21 1
223 3
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5
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Writing State
Consistent Updates
Writing Policy: Avoiding Disruption
Invariants• No forwarding loops• No black holes• Access control• Traffic waypointing
Writing Policy: Path for New Flow
• Rules along a path installed out of order?– Packets reach a switch before the rules do
40Must think about all possible packet and event orderings.
packets
Writing Policy: Update Semantics
• Per-packet consistency– Every packet is processed by– … policy P1 or policy P2 – E.g., access control, no loops
or blackholes• Per-flow consistency
– Sets of related packets are processed by– … policy P1 or policy P2,– E.g., server load balancer, in-order delivery,
…
P1
P2
Writing Policy: Policy Update
• Simple abstraction– Update entire configuration at once
• Cheap verification– If P1 and P2 satisfy an invariant– Then the invariant always holds
• Run-time system handles the rest– Constructing schedule of low-level updates– Using only OpenFlow commands!
42
P1
P2
Writing Policy: Two-Phase Update
• Version numbers– Stamp packet with a version number (e.g., VLAN tag)
• Unobservable updates– Add rules for P2 in the interior– … matching on version # P2
• One-touch updates– Add rules to stamp packets
with version # P2 at the edge• Remove old rules
– Wait for some time, thenremove all version # P1 rules
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Writing Policy: Optimizations
• Avoid two-phase update– Naïve version touches every switch– Doubles rule space requirements
• Limit scope – Portion of the traffic– Portion of the topology
• Simple policy changes– Strictly adds paths– Strictly removes paths
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Frenetic Abstractions
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SQL-likequeries
OpenFlowSwitches
ConsistentUpdates
Policy Composition
Related Work• Programming languages
– FRP: Yampa, FrTime, Flask, Nettle– Streaming: StreamIt, CQL, Esterel, Brooklet, GigaScope– Network protocols: NDLog
• OpenFlow– Language: FML, SNAC, Resonance– Controllers: ONIX, POX, Floodlight, Nettle, FlowVisor– Testing: NICE, FlowChecker, OF-Rewind, OFLOPS
• OpenFlow standardization– http://www.openflow.org/– https://www.opennetworking.org/
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Conclusion
• SDN is exciting– Enables innovation– Simplifies management– Rethinks networking
• SDN is happening– Practice: useful APIs and good industry traction– Principles: start of higher-level abstractions
• Great research opportunity– Practical impact on future networks– Placing networking on a strong foundation
47
Frenetic Project
http://frenetic-lang.org
• Programming languages meets networking– Cornell: Nate Foster, Gun Sirer, Arjun Guha, Robert Soule,
Shrutarshi Basu, Mark Reitblatt, Alec Story– Princeton: Dave Walker, Jen Rexford, Josh Reich, Rob
Harrison, Chris Monsanto, Cole Schlesinger, Praveen Katta, Nayden Nedev
Short overview at http://www.cs.princeton.edu/~jrex/papers/frenetic12.pdf