Transcript 2. Uniform high capacity between servers Enforce hose model using

Data Center Architectures
CIS 700/005 – Lecture 2
Includes material from lectures by Hakim Weatherspoon and Jennifer Rexford
Traditional Data Centers
Internet
Core
Aggregation
Access
Data Center
Layer-3 router
Layer-2/3 switch
Layer-2 switch
Servers
Limitation (1): Oversubscription
 Ratio of the worst-case achievable aggregate
bandwidth among the end hosts to the total
bisection bandwidth of a particular communication
topology
 Lower the total cost of the design
 Typical designs: factor of 2:5:1 (400 Mbps)to
8:1(125 Mbps)
Limitation (2): Fault tolerance
• Oversubscription + Bigger routers
 less routers at the top of the tree
 a core router failure has high blast radius
A Scalable, Commodity Data
Center Network Architecture
Mohammad Al-Fares, Alexander Loukissas, Amin Vahdat
• Scalable interconnection bandwidth
• 1:1 oversubscription
• Economies of scale
• Backwards compatibility
History Lesson: Clos Networks (1953)
• Emulate a single huge switch with many smaller switches
• Add more layers to scale out
History Lesson: Clos Networks (1953)
• Emulate a single huge switch with many smaller switches
• Add more layers to scale out
History Lesson: Clos Networks (1953)
• Emulate a single huge switch with many smaller switches
• Add more layers to scale out
Fat-tree Architecture
K-ary fat tree: three-layer topology (edge, aggregation and core)
• each pod consists of (k/2)2 servers & 2 layers of k/2 k-port switches
• each edge switch connects to k/2 servers & k/2 aggr. switches
• each aggr. switch connects to k/2 edge & k/2 core switches
• (k/2)2 core switches: each connects to k pods
Obligatory Network Questions
• How do I address destinations?
•
•
Hierarchical IP addresses for scalability
[PodNumber].[SwitchNumber].[Endhost]
• How does a switch route packets?
•
•
•
Assumption: every routing table entry has 1 output
Route downward using prefix (for scalability)
Route upward using suffix (for load balancing)
Routing Optimizations
1. Flow classification
• Classify flows (e.g., src, dest, port #s)
• Move around a small set of flows as needed
2. Flow scheduling
• Keep track of large, long-lived flows at the edge switches
• Assign them to different links
VL2: a scalable and flexible data
center network
A. Greenberg, J. R. Hamilton, N. Jain, S. Kandula, C. Kim, P.
Lahiri, D. A. Maltz, P. Patel, and S. Sengupta
• Let’s take the “single big switch” model to the limit:
• Uniform high capacity
• Performance isolation:
• Layer-2 semantics:
Virtual Layer 2 Switch (VL2)
1. L2 semantics
2. Uniform high
capacity
…
…
3. Performance
isolation
…
…
VL2 Goals and Solutions
Objective
1. Layer-2
semantics
2. Uniform
high capacity
between servers
3. Performance
Isolation
Approach
Employ flat
addressing
Solution
Name-location
separation &
resolution service
Guarantee bandwidth
for
hose-model traffic
Flow-based random traffic
indirection
(Valiant LB)
Enforce hose model
using existing
mechanisms only
TCP
“Hose”: each node has ingress/egress bandwidth constraints