This document discusses different SDN deployment models including centralized vs distributed control, symmetric vs asymmetric, flood-based vs floodless, host-based vs network centric, reactive vs proactive, and flow routing vs aggregation. Under centralized control, SDN global information is held at a central controller, while distributed control distributes information and functions across multiple controllers. Reactive systems install flow entries in response to traffic, while proactive systems pre-populate flow tables to avoid setup delays. Flow routing uses exact-match entries for fine-grained control, while aggregation uses wildcard entries for large numbers of flows.

1. NDI Communications - Engineering & Training
Software Defined Networking (SDN)
Chapter 4 – SDN Deployment Models

2. Page 2
Chapter Content
Introduction
Centralized vs Distributed Control
Flow Routing vs. Aggregation
2

3. Page 3
Introduction and Terms
Symmetric vs Asymmetric:
In an asymmetric model, SDN global information is centralized as much as possible, and edge driving is
distributed as much as possible.
In a symmetrically distributed SDN model, an effort is applied to increase global information
distribution ability, and SDN aggregation performance ability so that the SDN elements are basically
one type of component.
Floodless vs Flood-based:
In a flood-based model, significant amount of the global information sharing is achieved using well
known broadcast and multicast mechanisms.
In a FloodLess model, all forwarding is based on global exact match typically achieved using
Distributed Hashing and Distributed Caching of SDN lookup tables.
Host-based Vs Network Centric:
In a host-based model, under an assumption regarding use of SDN in data-centers with lots of virtual
machines moving to enable elasticity, the SDN encapsulation processing is already done at the
host HyperVisor on behalf of the local virtual machines.
In a Network Centric design, a clearer demarcation is made between network edge and end points.
Such an SDN edge is associated with the access of Top of Rack device and outside the host endpoints.

4. Page 4
Reactive vs. Proactive (pre-populated)
Reactive
First packet of flow
triggers controller to
insert flow entries
Efficient use of flow
table
Every flow incurs small
additional flow setup time
If control connection lost,
switch has limited utility
Proactive
Controller pre-populates
flow table in switch
Zero additional flow setup
time
Loss of control connection
does not disrupt traffic
Essentially requires
aggregated (wildcard)
rules

5. Page 5
Reactive vs. Proactive (pre-populated)
Reactive
First packet of flow
triggers controller to
insert flow entries
Efficient use of flow
table
Every flow incurs small
additional flow setup time
If control connection lost,
switch has limited utility
Proactive
Controller pre-populates
flow table in switch
Zero additional flow setup
time
Loss of control connection
does not disrupt traffic
Essentially requires
aggregated (wildcard)
rules

6. Page 6
Chapter Content
Introduction
Centralized vs Distributed Control
Flow Routing vs. Aggregation

7. Page 7
SDN Domains
OpenFlow
Switch
Domain
Controller
OpenFlow
Switch
OpenFlow
Switch
OpenFlow
Switch
OpenFlow
Switch
OpenFlow
Switch
OpenFlow Protocol
Domain
Controller
SDNi

8. Page 8
Chapter Content
Introduction
Centralized vs Distributed Control
Flow Routing vs. Aggregation

9. Page 9
Flow Routing vs. Aggregation
Flow-Based
Every flow is individually
set up by controller
Exact-match flow
entries
Flow table contains one
entry per flow
Good for fine grain
control, e.g. campus
networks
Aggregated
One flow entry covers
large groups of flows
Wildcard flow entries
Flow table contains one
entry per category of
flows
Good for large number of
flows, e.g. backbone
9

10. Page 10
Summary
Yoram Orzach
yoram@ndi-com.com
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