VL2: A Scalable and Flexible Data Center Network Albert Greenberg, James R. Hamilton, Navendu Jain, Srikanth Kandula, Changhoon Kim, Parantap Lahiri, David A. Maltz, Parveen Patel, Sudipta Sengupta Microsoft Research SIGCOMM Comput. Commum. Rev., Vol 39, No. 4. (2009) , pp.51-62

Outline Motivation Conventional Data Center Architecture Virtual Layer 2 (VL2) Design Advantage Evaluation Conclusion

Motivation Today’s data center network has several issues: The network is a bottleneck to Data Center computation. Today’s data center network has several issues: Tree architecture Congestion and computation hot spot Traffic Independence IP configuration Complexity Migration Tradeoff Reliability and utilization

Conventional Data Center Architecture packet flooding and ARP broadcasts

Design of VL2 Location-specific IP address(LAs)(public) For all switches and interfaces or external server Application-specific IP addresses (AAs)(private) For application servers VL2 Directory System Stores the mapping of AAs to LAs Access control

Scale-out Topologies Aggr : Int = n:m ToR : Aggr = 1:2

Scale-out Topologies Benefit Risk balancing The failure of a Int. reduces the bisection bandwidth by only 1/m Routing is extremely simple on this topology Random path up and random path down.

Randomly select Int. by ECMP Example Randomly select Int. by ECMP Create by VL2 Agent

VL2 agent VL2 agent’s work flow Intercepts the ARP request for the destination AA Converts ① to an unicast query to the VL2 directory system Intercepts packets from the host Encapsulates the packet with the LA address from ②. Caches the mapping from AA to LA addresses

Advantage of VL2 Building on proven networking technology: Load Balance Randomizing to Cope with Volatility: Building on proven networking technology: link-state routing, equal-cost multi-path(ECMP) forwarding, IP anycasting, IP multicasting Simple Migration Static AAs Only need to update AAs & LAs mapping Eliminating the ARP and DHCP scaling bottlenecks

Evaluation: testbed 80 servers Intermediate switches*3 5 for directory system Intermediate switches*3 24 10Gbps Ethernet ports(3 for Aggr) Aggregation switches*3 24 10Gbps Ethernet ports(3 for Aggr, 3 for ToR) ToR*4 24 1Gbps ports

Experiment objective We test the following three objectives Uniform high capacity Fairness Performance isolation

VL2 Provides Uniform High Capacity We create an all-to-all data shuffle traffic matrix involving 75 servers. Each of 75 servers deliver 500MB data other 74 servers - a shuffle of 2.7 TB from memory to memory. During the run, the sustained utilization of the core links in the Clos network is about 86%. (more than 10x what the network in our current data centers can achieve with the same investment)

VL2 Provides Fairness In the experiment before, we observe the 3 aggregate switch We use Jain’s fairness index[15] [15 R.Jain. The Art of Computer Systems Performance analysis, techniques for Experimental Design, Measurement, Simulation, and Modeling. John Wiley & Sons, INC, 1991.

VL2 Provides Performance Isolation

Conclusion VL2 provides The simpler abstraction that all servers assigned to them are plugged into a single layer 2 switch Hotspot free performance A simple design that can be realized today High utilization Achieves high TCP fairness.

Q&A I HAVE QUESTIONS!!