Pre$SDN era: network trends in data centre networking

Transcription

1 Pre$SDN era: network trends in data centre networking Zaheer Chothia Software Defined Networking: The Data Centre Perspective

2 Outline 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 2

3 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 3

4 Requirements of Modern Data Center Scalability GDeHcoupling Mobility Others Virtualized networks Optimized forwarding Cloud integration and many more 4

5 Requirements of Modern Data Center 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 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 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 5

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7 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 7

8 The Road to SDN: An Intellectual History of Programmable Networks 8

9 Spanning Tree Protocol GSTPH Purpose: Ensures loop`free topology by blocking redundant paths Common Spanning No load balancing possible; need to block one uplink for all VLANs CPU is spared; only one instance needs to be computed PerAVLAN Spanning 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 9

10 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: *15 = 50 seconds!i Patchwork: Rapid STP: faster convergence after a topology change Hwith active confirmationi Multiple STP: per`vlan spanning tree + block all but one of alternate paths within each Link Aggregation Group Hpresent as single linki 10

11 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 of virtual to physical topology 11

12 Bag of protocols Designed to address shortcomings mentioned earlier Typically employ encapsulation for transparency from host Hrather than for logical separationi Surveyed: layer`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 12

13 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 balancing Learn MAC addresses on all bridges along shortest path SPBM: uses B`MAC+B`VID HbackboneI to designate reachability C`MAC HclientI addresses are never learned or looked up in the core 13

14 Transparent Interconnection of Lots of Links GTRILLH Control plane: IS`IS for discovery and to distribute link`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 Several possible multicast trees More active paths Hefficient use of bandwidthi 14

15 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 15

16 Framing formats compared New encapsulation compatible with Ethernet bridges TRILL Ethernet frame FabricPath Variant 1 Variant 2 Extended segment ID G24$bitsH Supports over 16 million virtual networks 16

17 Bag of Protocols Keynote at 1 st 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

18 My take 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 18

19 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 19