SDN: Week 6: Module 7.1: Data centres

[gdt]

Data centres are used for cloud computing, where elastic infrastructure can be allocated as demands changes.
- software as a service
- platform as a service
- infrastructure as a service

Key enabling technology is virtualisation.
- applications run unmodified
- VMs can migrate, without knowledge of customer, depending on demand
- easier if a large layer 2 network

Requirements
- easy migration of VMs
- minimal configuration of switches
- efficient communication along forwarding paths
- loopfree
- failure detection fast effective

Pre-SDN datacentres
- core to internet via L3 router
- access switches to servers
- aggregation switches in the middle

Problems:
- core routers single point of failure
- links higher in topology may be oversubscribed
Therefore:
- multirooted fat tree

Need a large L2 topology
- minimal configuration
- scaling problems: state, avoiding flooding (ARP, etc), fast updates to addressing on a VM move

PortLand: SDN for data centre networks
- "fabric manager"
- each host has a pseudo MAC addr with heirarchical structure
- thus efficient forwarding
- need to intercept and re-write MAC addresses
- need to rewrite ARPs
- done by Fabric Manager

MAC learning
- new source MAC addresses are forwarded to Fabric Manager
- FM constructs mapping to pseudo MAC

ARP
- edge switch sends ARP to FM
- FM proxy ARPs, returning PMAC

Strong similarities to SDN.

Summary
- data centre networks have unique requirements for scaling and flexiblilty
- 10,000s servers
- minimal configuration and state
- quickly migrate VMs
- PortLand Fabric Manager is a early SDN controller for data centres
- using structured pseudo MACs and intercept-and-proxy ARP