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Frenetic: Programming Software Defined Networks
Jennifer Rexford
Princeton University
http://www.frenetic-lang.org/
Joint with Nate Foster, David Walker, Rob Harrison, Chris Monsanto, Cole Schlesinger, Mike Freedman, Mark Reitblatt, Joshua Reich
Traditional Networks
2
Data Plane (hardware)Forwards, filters, buffers, tags,rate-limits; collects statistics
Control Plane (software)Tracks topology; computesroutes; modifies data plane
Management PlaneMonitors traffic,
configures policy
Software Defined Networking (SDN)
3
API to the data plane(e.g., OpenFlow)
Logically-centralized control
Switches
Smart,slow
Dumb,fast
Momentum
• Everyone has signed on– Google, Facebook,
Microsoft, Yahoo, Verizon, Deutsche Telekom
• New applications– Host mobility– Server load balancing– Network virtualization– Dynamic access control– Energy-efficiency
• Real deployments
Programming OpenFlow Networks
5
Images by Billy Perkins
• The Good– Simple data plane abstraction– Logically-centralized architecture– Direct control over switch policies
• The Bad– Low-level programming interface– Functionality tied to hardware– Explicit resource control
• The Ugly– Non-modular, non-compositional– Programmer faced with challenging
distributed programming problem
Language-Based Abstractions
• Benefits– Modularity– Portability– Efficiency– Assurance– Simplicity
Simple, high-level abstractions are crucial for achieving the vision of software-defined networking.
OpenFlow Networks
7
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
8
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
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
Application
Events from switchesTopology changes,
Traffic statistics,Arriving packets
Commands to switches(Un)install rules,Query statistics,
Send packets
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
11
Programming Abstractions for Software Defined Networks
12
Three Main Abstractions
13
Reading state
OpenFlowSwitches
Writingpolicies
Composing modules
Reading State: Multiple Rules
• Traffic counters– Switch counts bytes and packets matching a rule– Controller application polls 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
14
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
15
1. srcip = 1.2.3.41. 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
16
packets
Reading: Extra Unexpected Events
• More packets arrive before rules installed?–Multiple packets reach the controller
17
packets
Reading: Extra Unexpected Events
• Solution: suppress extra events–Programmer specifies “Limit(1)”–Run-time system hides the extra events
18
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
19
Select(bytes) *Where(in:2 & srcport:80) *GroupBy([dstmac]) *Every(60)
Select(packets) *GroupBy([srcmac]) *SplitWhen([inport]) *
Limit(1)
Learning Host Location
Traffic Monitoring
Composition: Multiple Modules
• Networks have multiple policies–Routing–Traffic monitoring–Access control
• Challenges–Common set of rules in the switches–Processing the same packets
• OpenFlow API is not modular–Programmer must combine the logic
20
Composition: Simple Repeater
def switch_join(switch): # Repeat Port 1 to Port 2 p1 = {in:1} a1 = [out:2] install(switch, p1, DEFAULT, a1) # Repeat Port 2 to Port 1 p2 = {in:2} a2 = [out:1] install(switch, p2, DEFAULT, a2)
def switch_join(switch): # Repeat Port 1 to Port 2 p1 = {in:1} a1 = [out:2] install(switch, p1, DEFAULT, a1) # Repeat Port 2 to Port 1 p2 = {in:2} a2 = [out:1] install(switch, p2, DEFAULT, a2)
Simple Repeater
1 2
Controller
When a switch joins the network, install two forwarding rules.
Composition: Web Traffic Monitor
22
def switch_join(switch)): # Web traffic from Internet p = {in:2, srcport:80} install(switch, p, DEFAULT, []) query_stats(switch, p) def stats_in(switch, p, bytes, …) print bytes sleep(30) query_stats(switch, p)
def switch_join(switch)): # Web traffic from Internet p = {in:2, srcport:80} install(switch, p, DEFAULT, []) query_stats(switch, p) def stats_in(switch, p, bytes, …) print bytes sleep(30) query_stats(switch, p)
Monitor “port 80” traffic
1 2
Web traffic
When a switch joins the network, install one monitoring rule.
Composition: Repeater + Monitor
def switch_join(switch): pat1 = {in:1} pat2 = {in:2} pat2web = {inport:2, srcport:80} install(switch, pat1, DEFAULT, None, [out:2]) install(switch, pat2web, HIGH, None, [out:1]) install(switch, pat2, DEFAULT, None, [out:1]) query_stats(switch, pat2web)
def stats_in(switch, xid, pattern, packets, bytes): print bytes sleep(30) query_stats(switch, pattern)
def switch_join(switch): pat1 = {in:1} pat2 = {in:2} pat2web = {inport:2, srcport:80} install(switch, pat1, DEFAULT, None, [out:2]) install(switch, pat2web, HIGH, None, [out:1]) install(switch, pat2, DEFAULT, None, [out:1]) query_stats(switch, pat2web)
def stats_in(switch, xid, pattern, packets, bytes): print bytes sleep(30) query_stats(switch, pattern)
Repeater + Monitor
Must think about both tasks at the same time.
Composition: Frenetic is Modular
24
# Static repeating between ports 1 and 2def repeater(): rules=[Rule(in:1, [out:2]), Rule(in:2, [out:1])] register(rules)
# Static repeating between ports 1 and 2def repeater(): rules=[Rule(in:1, [out:2]), Rule(in:2, [out:1])] register(rules)
# Monitoring Web trafficdef web_monitor(): q = (Select(bytes) * Where(in:2 & srcport:80) * Every(30)) q >> Print()
# Monitoring Web trafficdef web_monitor(): q = (Select(bytes) * Where(in:2 & srcport:80) * Every(30)) q >> Print()
# Composition of two separate modulesdef main(): repeater() web_monitor()
# Composition of two separate modulesdef main(): repeater() web_monitor()
Repeater
Monitor
Repeater + Monitor
Composition: Reactive Run-Time
• Microflow-based– Send first packet to
the controller– Install rule if possible
• Check all policies– Accumulate actions to
perform on packet
• Check all queries– If no matches: install a
rule to handle remaining packets of the flow
25
Composition: Proactive [POPL’12]
• Proactive, wildcard rules– Keep packets in the “fast path”
• “Cross-product” of predicates
• Translate predicates into rules– Convert each predicate to one or more rules– Minimize to produce a smaller set of rules
• Reactive specialization– Dynamically expanding the policy as packets arrive 26
in:1in:2*
in:2 & srcport=80*
X
in:1in:2 & srcport=80in:2*
=
Writing Policy: Avoiding Disruption
Writing Policy: Avoiding Disruption
Reasons• Routine maintenance• Unexpected failure• Traffic engineering• Fine-grained security
Invariants• No forwarding loops• No black holes• Access control• Traffic waypointing
Writing Policy: Traffic Engineering
• Shortest-path routing–Controller computes shortest paths–… based on preconfigured link weights
29
1
1
3
1
1
Writing Policy: Traffic Engineering
• Transient loop–Update top switch to forward down–… while bottom switch still forwards up
30
1 5
1
3
1
1
Writing Policy: Path for a New Flow
• Rules along a path installed out of order?–Packets reach a switch before the rules do
31Must 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, – … but not a mixture of the two– E.g., access control, no loops
or blackholes during routing change
• Per-flow consistency– Sets of related packets are processed by– … policy P1 or policy P2,– … but not a mixture of the two– E.g., server load balancing, in-order delivery, …
P1
P2
Writing Policy: Policy Update
• Simple abstraction– Update the entire configuration at once– E.g., per_packet_update(P2)
• 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– Applying optimizations to limit the number of rules– Using only OpenFlow commands!
33
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, then
remove all version # P1 rules34
Writing Policy: Optimizations
• Avoid two-phase commit– Naïve version touches every switch– Doubles rule space requirements
• Limit scope of two-phase commit– Affects only a portion of the traffic– Affects only a portion of the topology
• Simple policy changes– Extension: strictly adds paths– Retraction: strictly removes paths
• Run-time system applies optimizations35
Frenetic Abstractions
36
SQL-likequeries
OpenFlowSwitches
ConsistentUpdates
Policy Composition
Ongoing Work
• Network virtualization– Applications see abstract topology– E.g., one big switch
37
Ongoing Work
• Network virtualization– Applications see abstract topology– E.g., one big switch
• Joint host-network management– Measurement and control– … through local host agent
38
Ongoing Work
• Network virtualization– Applications see abstract topology– E.g., one big switch
• Joint host-network management– Measurement and control– … through local host agent
• Policy transformation– Spread rules over many switches– E.g., distributed firewall/load-balancer
39
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, Nettle, FlowVisor, RouteFlow– Testing: MiniNet, NICE, FlowChecker, OF-Rewind,
OFLOPS
• OpenFlow standardization– http://www.openflow.org/– https://www.opennetworking.org/ 40
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 41
Concern
Assembly Languages
Programming Languages
x86 NOX Java/ML Frenetic
Resource Management
Move values to/from register
Declare/use variables
ModularityUnregulated
calling conventions
Calling conventions
managed automatically
ConsistencyInconsistent
memory model
Consistent (?) memory model
PortabilityHardware dependent
Hardware independent
Concern
Assembly Languages
Programming Languages
x86 NOX Java Frenetic
Resource Management
Move values to/from register
(Un)Install policy
rule-by-rule
Declare/use variables
Declare network policy
ModularityUnregulated
calling conventions
Unregulated use of
network flow space
Calling conventions
managed automatically
Flow space managed
automatically
ConsistencyInconsistent
memory model
Inconsistentglobal
policies
Consistent (?) memory model
Consistent global policies
PortabilityHardware dependent
Hardware dependent
Hardware independent
Hardware Independent
Thanks to My Frenetic Collaborators
44
Nate Foster Dave Walker Chris Monsanto Mark Reitblatt
Mike FreedmanRob Harrison Alec Story Josh Reich