Pre$SDN era: network trends in data centre networking

Zaheer Chothia – 27.02.2015 Software Defined Networking: The Data Centre Perspective

Outline

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Challenges and New Requirements History of Programmable Networks Spanning Tree Protocol HSTPI

Network Overlay Technologies Examples: SPB, TRILL, FabricPath, MPLS

Emerging Next$Generation Protocols SDN and OpenFlow

Networks have not kept pace “In the modern data center, traditional technologies are limiting the speed, flexibility, scalability, and manageability of application deployments.” Cloud data center networks must contend with: •  huge numbers of attached devices Hboth physical and virtualI •  large numbers of isolated independent subnetworks •  multitenancy Hdifferent tenants collocated on a single hostI •  automated creation, deletion, and migration of virtual machines

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Requirements of Modern Data Center

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GDeHcoupling

Scalability

Mobility

Others •  Virtualized networks •  Optimized forwarding •  Cloud integration •  … and many more

Requirements of Modern Data Center

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GDeHcoupling Physical/logical connectivity Want to deploy and expand workloads anywhere Can extend VLAN domain but this affects availability Hlarger fault domainI + reconfiguration and administrative overhead Infrastructure and policy Common practice: •  Group entities with like

membership into a VLAN •  IP addressing schemes based

on subnet boundaries Results in many inefficiencies and limitations Hcyclic changeI

Scalability More end hosts and isolated subnetworks Forwarding tables Network uses end`host information HIP/MAC addressI to make forwarding decisions Need to propagate this state across entire data center fabric Network segments Space limitations: 802.1Q supports at most 4,094 VLANs Also desired: •  traffic management •  secure segmentation •  performance isolation

Mobility Use case: live migration of VMs Need to retain adequate network state Address of end host should be independent of location in the network

Others •  Virtualized networks •  Optimized forwarding •  Cloud integration •  … and many more

6 https://www.nanog.org/meetings/nanog50/presentations/Sunday/IEEE_8021aqShortest_Path.pdf

20 years of development •  Active Networking

–  Mid`90s: Internet took off; standardization is too slow! –  Approach: programmable functions in the network –  Capsule model Hcode to execute at nodes carried in`band in data packetsI

•  Separating Control and Data Planes –  Early 2000s: increasing traffic volumes and greater emphasis on network reliability,

predictability, and performance –  Desired: better control of paths used to deliver traffic Htraffic engineeringI –  Logically centralized control + open interfaces to routers and switches

•  OpenFlow API and Network OSes –  Network experimentation at scale Hencouraged by successes of PlanetLab/EmuLabI –  Pragmatism: limit flexibility Hbuild on existing switchesI, but immediate deployability –  First widespread adoption of an open interface

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The Road to SDN: An IntellectualHistory of Programmable Networks

8 https://www.cs.princeton.edu/~jrex/papers/queue14.pdf https://www.youtube.com/watch?v=dkUDUb9GtH0

Spanning Tree Protocol GSTPH Purpose: Ensures loop`free topology by blocking redundant paths

9 http://www.cisco.com/c/en/us/support/docs/lan`switching/spanning`tree`protocol/24248`147.html

Common Spanning Tree ?CST@ •  No load balancing possible; need to block one uplink

for all VLANs •  CPU is spared; only one instance needs to be

computed PerAVLAN Spanning Tree ?PVST@ •  Optimum load balancing Hodd`evenI •  1000 separate instances Hfor each VLANI even though

only two different final topologies •  Considerably wastes CPU cycles for all of the switches

in the network

STP drawbacks •  Designed with maximum stability and safety in mind •  Blocking redundant ports: squandered aggregate bandwidth •  Cannot HeasilyI segregate into smaller domains

Desirable for scalability, fault isolation, multi`tenancy •  Topology change: network halts while STP recalculates [see link below]

–  Bounded by Max_Age+2xForward_Time Htypical: 20 + 2*15 = 50 seconds!I

10 http://blog.ine.com/wp`content/uploads/2011/11/understanding`stp`rstp`convergence.pdf

•  Patchwork: –  Rapid STP: faster convergence after a topology

change Hwith active confirmationI –  Multiple STP: per̀ VLAN spanning tree + block all

but one of alternate paths within each –  Link Aggregation Group Hpresent as single linkI

Network Overlays Benefits •  Simplified management •  Multi`tenancy: scalable beyond 4000

VLANs •  Workload`anywhere Hmobility and

reachabilityI •  Arbitrary forwarding topologies over fixed

underlay Challenges •  Decreased visibility: traceroute in overlay

will not report individual underlay hop counts

•  Troubleshooting complexity:need to investigate mapping ofvirtual to physical topology

11 http://etherealmind.com/integrating`overlay`networking`and`the`physical`network/

Bag of protocols •  Designed to address shortcomings mentioned earlier •  Typically employ encapsulation for transparency from host

Hrather than for logical separationI •  Surveyed: layer̀ 2 ECMP designs with multipath routing

–  Shortest Path Bridging HSPBI –  Transparent Interconnection of Lots of Links HTRILLI –  Cisco FabricPath –  Brocade: Virtual Cluster Switching HVCSI

Based on TRILL Hdata planeI; doesn’t use IS`IS core –  Juniper: QFabric Hshelved?I

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Shortest Path Bridging GSPBH •  Consolidate into a one link state protocol:

–  STP, Multiple STP, Rapid STP –  Multichassis Link Aggregation –  Multiple MAC Registration Protocol HMMRPI

•  Service identifiers HI`SIDI for independence from backbone MAC address / VLAN IDs

•  New device: learn its immediate neighbourhood, compute shortest bidirectional paths using link metrics Hsuch as ECMPI

•  End points are fully aware of entire traffic path Hunlike TRILLI •  Two modes

–  SPBV: use VLAN ID for delineation and load balancingLearn MAC addresses on all bridges along shortest path

–  SPBM: uses B`MAC+B`VID HbackboneI to designate reachabilityC`MAC HclientI addresses are never learned or looked up in the core

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Transparent Interconnection of Lots of Links GTRILLH •  Control plane: IS`IS for discovery and to distribute link̀ state

database Heach node has state of entire networkI •  Uses Routing Bridges HRBridgesI to provide:

–  Shortest unicast paths Hunlike STP: no single tree constraintI –  Faster convergence times –  Load splitting over multiple paths –  Loop mitigation –  MAC scalability: relegated learning to the edge RBs

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•  Several possible multicast trees •  More active paths Hefficient use

of bandwidthI

http://www.slideshare.net/IssacYuan/trill`spbcomparisonextract

Cisco FabricPath •  Proprietary implementation of TRILL

–  Control plane: utilizes TRILL Hincluding IS`IS for L2 multipath routingI –  Data plane: non`interoperable

•  Forwarding tag GFTAGH –  for multi`destination, unicast frames; –  assigned on the edge port, honored throughout; –  selects one of multiple paths Hmax 1024I that the packet traverses

•  Conversational MAC learning –  interface learns source MAC of ingress frame only if destination MAC is

already present in the table –  i.e. only learn if remote device is having a bidirectional conversation with a

locally connected device –  unknown unicast frames being flooded: no learning on edge switches

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Framing formats compared

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TRILL Ethernet frame

FabricPath

Extended segment ID G24$bitsHSupports over 16 million virtual networks

Variant 1

Variant 2

New encapsulation compatible with Ethernet bridges

Bag of Protocols •  Keynote at 1st Open Networking Summit in 2011

“The Future of Networking, and the Past of Protocols” – Scott Schenker •  Why does networking lag behind?

–  “… because of your great ability to master complexity” •  Future of networking lies in finding right abstractions

–  “The era of ‘a new protocol per problem’ is over” •  SDN is defined precisely by these three abstractions

–  “Distribution, forwarding, configuration” •  SDN not just a random good idea…

–  “... can be “derived” from decomposing network control”

17 http://opennetsummit.org/archives/oct11/shenker̀ tue.pdf https://nerdtwilight.wordpress.com/2012/02/13/sdn`aims`to`ditch`bag`of̀ protocols/

My take

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1.  Thankful I am not a protocol designer! 2.  Decoupling: limited integration between overlay and underlay 3.  Are the original problems fully addressed?

HHard to judge from the fencepostI

Discussion •  Uninitiated / new format for me •  6 critique / 2 in defense

http://digital.hammacher.com/Items/74670/74670_1000x1000.jpg

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T2: SDN basics and the Open Flow protocol •  A Survey of Software`Defined Networking: Past,

Present, and Future of Programmable Networks •  Network Innovation using OpenFlow: A Survey