1. 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

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

3. 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

4. Conventional Data Center Architecture
packet flooding and ARP broadcasts

5. 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

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

7. 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.

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

9. 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

10. 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

11. 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

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

13. 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)

14. 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.

15. VL2 Provides Performance Isolation

16. 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.

17. Q&A
I HAVE QUESTIONS!!