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PortLand: A Scalable Fault-Tolerant Layer 2

Data Center Network FabricB97703099 財金三 婁瀚升

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Outline

• Introduction• Background• Design• Implementation• Conclusion

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Introduction

• LAN insufficiency • Requirement Network in datacenter :– VM Migration without IP change– Needn’t config switch before deployment– Host in datacenter efficiently communicate– No forwarding loop– Fault-tolerant and recovery

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Introduction• Layer 2 kind fabric– Layer 3 not workable• VM migration with IP change• Config switches of subnet and DHCP synchronite

• TTL method: prevent forwarding loop• Prevent routing broadcast

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Background:DatacenterNetwork• Topology• Forwarding– Layer 3 : IP assigned hierachically• Broadcast (Failure avoidance, overhead )• Config switch subnet & DHCP syncro. Fault• VM migration unable

– Layer 2 : MAC• Single spanning tree problem (not shortest way)• Broadcast entire fabric

– VLAN : • Source pre-assignment (decrease flex. & scal.)• Switch need to maintain VLAN’s state

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• End host Virtualization– Layer 3 setting : not work– ARP to solute ?

Background:DatacenterNetwork

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Fat Tree Network

• Multi-rooted• Stage : edge, aggregation, core• K-port swithes:– k3/4 end hosts– 5k2/4 individual k-port switches– k individual pods– each pod : k2/4 hosts

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Design : Fabric Manager• Centralized Manager• Fuction :– Mantain soft state network config (ex.topology)– Responsible for • ARP resolution• Fault tolerance• Multi-cast

• Only soft state (no hard state, ex.#of switch)

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Design : Pseudo MAC

• Assigned to end hosts• Information include:– Location : same pod, same prefix– Pod number→ position numer

• End host with their own AMAC• LDP (location discovery protocol)– employed to assign– Pod.position.port.vmid

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Design : Proxy-based ARP

• Ethernet : B-cast to all host(same layer2)• Used for communication in datacenter• If FM not available for IP-PMAC mapping

→bcat to core(O(k) state )• VM migration supporting– FM sending invalidation message to old pos.– If contact with this message

→ new PMAC address in the host’s cache

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Design : Distributed Location Discovery• Location Discovery Protocol (LDP)• No administative config (no manul set)• Location Discovery Message:– Sent by switches– Several information – Edge got from aggregation, learned

→Aggregation learned →Core learned

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Design : Distributed Location Discovery

• Location Discovery Message:– Position number acquisition:• Randomly chosen number• Verified by aggregation

– Pod number acquisition:• FM assignment to aggregation

– Exception : non-existence• LDM not correct• Disable suspicious port

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Design:Loop free Forwarding

• Prevent using Spanning tree• Downward seperate from Upward

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Design : Fault Tolerance

• Unicast Fault Detection and Action• Multicast Fault Detection and Action

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Deisign : Comparison

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Implementation : System

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Implementation :Evaluation

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Implementation :Evaluation

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Implementation :Evaluation

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Implementation :Evaluation

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Implementation :Evaluation

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Implementation :Evaluation

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Conclusion

• Commercial Use• Datacenter Network Protocol