16. Software Defined Networking

Question 1

SW defined networking

Answer 1

An approach to computer networking that allows network administrators to manage network services through abstraction of lower level functionality. This is done by decoupling the system that makes decisions about where traffic is sent (the control plane) from the underlying systems that forward traffic to the selected destination (the data plane). The inventors and vendors of these systems claim that this simplifies networking.

Question 2

Open Flow

Answer 2

SDN requires some method for the control plane to communicate with the data plane. One such mechanism, OpenFlow, is often misunderstood to be equivalent to SDN, but other mechanisms could also fit into the concept.

Question 3

Existing switching / routing

Answer 3

Uses deticated hardware

- commonly combined in one device

Question 4

Routers

Answer 4

Control plane - routing protocol creates the Routing Information Base (RIB)

Data Plane - Forwarding information base (FIB), written by control plane, from RIB information it holds

Management plane - via ssh, via SNMP

Question 5

Switches

Answer 5

Dumb devices, optimised for layer 2 switching

Some additional capability, ACLs, DHCP snooping

Question 6

Key SDN concepts

Answer 6

Separation of control and data plane
Centralising network ‘intelligence’ (through controler device/s)
Enabling a ‘programmable’ network (through control protocol -eg Open Flow, running between the controller and the underlying network devices)
Highly dynamic
- can be per flow, on demand
Rapid provisioning
Rapid innovation
- no need to wait for new features from vendors
- can empower network owners

Question 7

SDN driver/motivation

Answer 7

Changing traffic patterns
- emerging data centre requirements
- need elasticity in services
- be able to meet pek demand, big data, peak hours
- but don’t pay for capacity in quiet periods
Abstraction of services from hardware
- firewalls, IDS
- need to be able to control traffic paths
SDN can virtualise compute and storage functions

Question 8

SDN might provide answers for:

Answer 8

Complexity
Consistency
Scalability
Vendor independence

Question 9

SDN -> complexity

Answer 9

devices have many protocols working in isolation

results in tendency for networks to be static

Question 10

SDN -> consistency (across a network)

Answer 10

Simpler devices, single logical control point

Question 11

SDN -> Scalability

Answer 11

with flexibility

Question 12

SDN -> Vendor Independence

Answer 12

Through generic interfaces to underlying functions

Underlying equipment interoperable eg via openFlow

Question 13

OpenFlow fm wikipedia

Answer 13

OpenFlow is a communications protocol that gives access to the forwarding plane of a network switch or router over the network.

Question 14

OpenFlow more

Answer 14

OpenFlow enables remote controllers to determine the path of network packets through the network of switches. This separation of the control from the forwarding allows for more sophisticated traffic management than is feasible using access control lists (ACLs) and routing protocols. Also, OpenFlow allows switches from different suppliers — often each with their own proprietary interfaces and scripting languages — to be managed remotely using a single, open protocol.

Question 15

OpenFlow Tim’s

Answer 15

Open interface to packet forwarding
Provides forwarding abstraction
- one part is protocol
- one part is configuration

Question 16

OpenFlow Instruction set

Answer 16

• OF provides a “Match - Action” model
• Instructions can be programmed dynamically
• Allows a controller to populate a device flow table (if this than that rules)
• Default action is usually to send packet to controller
• Provides an abstraction of how all forwarding works today, as a set of match - action instructions

Question 17

Programming the network

Answer 17

Intelligence lies with the controller
Can implement whatever  algorithms you like in the controller for provisioning the devices
Many open source controllers available
Strategies 
 - can prepopulate the flow table
 - can program on the fly

Question 18

Standards development

Answer 18

To be interoperable, still need standards
Open Networking Foundation (ONF)
Internet Engineering Task Force (IETF)
European Telecommunications Standards Institute (ETSI)

Question 19

SDN Scenarios

Answer 19

Data centres, cloud computing, campus networks, home networks, cellular access networks…

Question 20

SDN Use Cases

Answer 20

Load balancing, enabling QoS, enforcing security policies, IPV6 transition, DDoS mitigation, device quarantining…

Growing vendor support; many switches, routers & sw controllers