pre$sdn era: network trends in data centre networking · across entire data center fabric network...
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Pre$SDN era: network trends in data centre networking
Zaheer Chothia – 27.02.2015 Software Defined Networking: The Data Centre Perspective
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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
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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
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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
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6 https://www.nanog.org/meetings/nanog50/presentations/Sunday/IEEE_8021aqShortest_Path.pdf
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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
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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
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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
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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/
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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
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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
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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/
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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
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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