4. SDN & NFV

Question 1

What is the main idea of software defined networking?

Answer 1

Separate the data and control plane:
- Switches: dumb and fast
- Controller: slow and smart

Question 2

What are the main components of SDN?

Answer 2

From top to bottom:
Application layer (e.g. routing, firewall, traffic engineering)
– Northbound API –
Network OS
– Southbound API –
Data plane (Data forwarding based on forwarding rules)

Question 3

What is OpenFlow?

Answer 3

Communication protocol between control- and data plane

Question 4

What are the packet-handling rules?

Answer 4

• Pattern: match packet header bits
• Actions: drop, forward, modify, send to controller
• Priority: disambiguate overlapping patterns
• Counters: #bytes and #packets

Question 5

What are PISA and P4?

Answer 5

PISA = Programming Protocol-independent Packet Processors:
- Concept of a programming language for data plane consisting of:
- Parser -> Match-Action Pipeline -> Deparser
P4: Implementation of PISA

Question 6

How does OpenFlow work?

Answer 6

• OpenFlow controller manipulates the flow tables on the switches.
• If an entry matches perform that action
• Otherwise forward to OpenFlow controller

Question 7

What is the structure of a P4 program?

Answer 7

• Header: Structure that defines the specific packet header bits
• Parser: State machine, which defines how packet headers are extracted
• Match-Action Pipeline:
  – Action: defines actions to apply (e.g. ip4_forward())
  – Table: defines what actions to apply if certain field matches
  — Match types: Longest prefix match, exact, ternary, range
  – Control: defines control flow (which tables to use in which order)
• Deparser: Put packet back together

Question 8

What is the motivation for SDN and NFV?

Answer 8

NFV: Middleboxes are..
- Expensive
- Inflexible (service deployment takes long)
- Time consuming and error-prone
SDN: Traditional router offer limited functionality and no modularity