Lecture 7: Data Center Networks

Transcription

1 Lectre 7: Data Center Networks CE 222A: Compter Commnication Networks Alex C. noeren Thanks: Nick Feamster

2 Lectre 7 Overview Project discssion Data Centers overview Fat Tree paper discssion CE 222A Lectre 7: Data Center Networks 2

3 Traditional DC Topology Core Internet Layer-3 roter Data Center Aggregation Layer-2/3 switch Access Layer-2 switch ervers CE 222A Lectre 7: Data Center Networks 3

4 DC Network Reqirements calability Incremental bild ot? Reliability Loop free forwarding VM migration Reasonable management brden Hmans in the loop? CE 222A Lectre 7: Data Center Networks 4

5 Traditional Topologies Over sbscription of links higher p in the topology Tradeoff between cost and provisioning ingle point of failre CE 222A Lectre 7: Data Center Networks 5

6 Capacity Bottlenecks CR CR ~ 200:1 AR AR AR AR ~ 40:1 ~ 5:1... A A A A A A A A A A A A CE 222A Lectre 7: Data Center Networks 6

7 Management: L2 vs. L3 Ethernet switching (layer 2) Cheaper switch eqipment Fixed addresses and ato-configration eamless mobility, migration, and failover IP roting (layer 3) calability throgh hierarchical addressing Efficiency throgh shortest-path roting Mltipath roting throgh eqal-cost mltipath Data centers often connect layer-2 islands by IP roters CE 222A Lectre 7: Data Center Networks 7

8 Advantages of Layer 2 Certain monitoring apps reqire server with same role to be on the same VLAN Using same IP on dal homed servers Allows organic growth of server farms VM migration is easier CE 222A Lectre 7: Data Center Networks 8

9 Layer 2 Pods w/l3 Backbone Internet DC-Layer 3 DC-Layer 2 CR CR... AR AR AR AR... A A A A A A ~ 1,000 servers/pod == IP sbnet Key CR = Core Roter (L3) AR = Access Roter (L3) = Ethernet witch (L2) A = Rack of app. servers CE 222A Lectre 7: Data Center Networks 9

10 FAT Tree-Based oltion An all Layer-3 soltion Connect end-host together sing a fat-tree topology Infrastrctre consist of cheap devices» Each port spports same speed as endhost All devices can transmit at line speed if packets are distribted along existing paths A k-port fat tree can spport k 3 /4 hosts CE 222A Lectre 7: Data Center Networks 10

11 Fat-Tree Topology CE 222A Lectre 7: Data Center Networks 11

12 Fat-Tree Challenges Layer 3 will only se one of the existing eqal cost paths Packet re-ordering occrs if layer 3 blindly takes advantage of path diversity E.g., ECMP CE 222A Lectre 7: Data Center Networks 12

13 Modified Fat Tree Enforce special addressing scheme in DC Allows host attached to same switch to rote only throgh switch Allows inter-pod traffic to stay within pod nsed.podnmber.switchnmber.endhost Use two level look-ps to distribte traffic and maintain packet ordering. CE 222A Lectre 7: Data Center Networks 13

14 Two-Level Lookps First level is prefix lookp Used to rote down the topology to endhost econd level is a sffix lookp Used to rote p towards core Diffses and spreads ot traffic Maintains packet ordering by sing the same ports for the same endhost CE 222A Lectre 7: Data Center Networks 14

15 Diffsion Optimizations Flow classification Eliminates local congestion Assign to traffic to ports on a per-flow basis instead of a perhost basis Flow schedling Eliminates global congestion Prevent long lived flows from sharing the same links Assign long lived flows to different links CE 222A Lectre 7: Data Center Networks 15

16 Discssion VM mobility Data center bild ot Internet connectivity Address space allocation Doing flow placement anyway? CE 222A Lectre 7: Data Center Networks 16

17 The Beaty of Ethernet Flat addressing and self-learning enables plg-and-play networking Permanent and location independent addresses also simplify Host mobility Access-control policies Network trobleshooting CE 222A Lectre 7: Data Center Networks 17

18 Ethernet caling Challenges Flooding-based delivery Frames to nknown destinations are flooded Broadcasting for basic service Bootstrapping relies on broadcasting Vlnerable to resorce exhastion attacks Inefficient forwarding paths Loops are fatal de to broadcast storms; ses TP Forwarding along a single tree leads to inefficiency and lower tilization CE 222A Lectre 7: Data Center Networks 18

19 Traditional L2/L3 Model Enterprise networks comprised of Ethernet-based IP sbnets interconnected by roters Ethernet Bridging - Flat addressing - elf-learning - Flooding - Forwarding along a tree Broadcast Domain (LAN or VLAN) R R R IP Roting (e.g., OPF) - Hierarchical addressing - bnet configration - Host configration - Forwarding along shortest paths R R CE 222A Lectre 7: Data Center Networks 19

20 For Next Class Read and review PortLand paper Work on project proposals Details available on the corse Web page CE 222A Lectre 7: Data Center Networks 20