9-Software Defined Networking Flashcards
What is network management
Process of configuring network to achieve a variety of tasks
Network configurations achieve a variety of tasks:
- Load Balance
- Security
- Business Relationships
Configuration mistakes can lead to
1) Oscillation - Routers cant agree on a route to a destination
2) Loops - Packets get stuck between two or more routers and never make it to the destination
3) Partitions - The network is split into two or more segments that are not connected.
4) “Black Holes” - Packets reach a router that does not know what to do with the packet and drops instead of sending to destination
Why is configuration hard?
SDN changes this
1) Defining Correctness is hard
2) Interactions between protocols -> unpredictability
3) Operators make mistakes
SDN provides operators 3 things
1) Network wide views
-topology and traffic
2) Network-level objectives
-load balance and security
3) Direct control
0>direct manipulation of data plane
Routers should
1) Forward packets
2) Collect measurements (statistics and topology info)
Routers should not
Compute routes
SDN
Removes routing from routers
What is SDN?
1) Logically centralized control
2) Network-wide control
Today: control and data planes run on routers
Data plane: Forward traffic
Control plane: compute routing tables
First in 2004 was the RCP (resource control protocol)
Worked on BGP only
2004: RCP
2005: 4D
2008: Openflow
History
Advantages of SDN
1) Coordination
2) Easy to evolve
3) Reasoning
All because of separate control plane
Control plane:
Software Program (i.e. Python, C…)
Logic that controls forwarding behavior
examples: routing protocols, configuration for network middleboxes
Data plane:
Programmable hardware (controlled by the control plane) Forward traffic according to control plane logic examples: forwarding, switching
SDN Application
Data Centers * Backbone Networks * Enterprise Networks * IXPs Home Networks
This course will focus on 1st 3 *
Examples of control plane operations?
1) Computing a forwarding path that satisfies a high level policy
2) Computing a shortest path routing tree
3) Authenticating a users device based on MAC Addresses
Why separate data and control plane?
1) independent evolution -> software & hardware can evolve independently
2) Control from high-level program -> allows operators to debug and check behavior easily
Why separate data and control plane?
1) Data centers: VM migration
2) Routing: More control over decision logic
3) Enterprise networks: Security
4) Research networks: Coexistense with production networks
Why separate data and control plane? Quiz
1) Independent evolution of data and control plane
2) Separating vendor hardware from control logic
3) Easier reasoning about network behavior
Data centers
SDN helps with VM migrations
How does control/data separation make managing data centers easier?
1) Monitoring/control of routers from a central point
2) Migrating VMs without renumbering hosts addresses
Why separate data and control plane?
Backbone security
Goal: filter the attack traffic
Challenges for SDN
1) Scalability: Hundreds to thousands of switches
2) Consistency: ensuring different replicas to see same view
3) Security/Robustness: Failure or compromise?
Ways to cope with scalability challenges?
1) Eliminate redundant data structures
2) Only perform control-plane operations for a limited # of ops
3) Cache forwarding decisions in switches
4) Run multiple controllers
Different SDN controllers
NOX, RYU, FLOODLIGHT (This lesson)
PYRETIC, FRENETIC (Programming SDN)
NOX
*First generation Openflow controller ->open-source, stable, widely used
Two flavors:
-Classic: C++, PYTHON
-New NOX: C++ only, fast, clean
NOX Architecture
Components: 1) Switches
2) Network-attached servers
Abstraction: Switch control
Control: Flow granularity
What is a Flow?
(header: counter, actions)
header= 10 tuple
counter
actions = forward, drop, sending to controller
NOX: Programmatic Interface
Performance is good but requires an understandings of low-level openflow commands and C++
When to use POX???
Class project or University research but NOT in a large internet datacenter because it does not perform as well as other controllers.
RYU
Python, OF 1.0,1.2,1.3, Open Stack
Floodlight
Java, OF 1.0, fork from “beacon”, Good documentation and performance… but has a steep learning curve.
NOX
C++, OF 1.0, good performance, slow programming/debugging hard
POX
Python, OF 1.0, performance ok… not the best, easy to program
POX Algoritm for Switch
See Udacity video #17
Modifying forwarding behavior is easy!
Switching:
Flow switching:
Firewall:
Caching
Customizing control is easy
1) Packets only reach controller if no flow table entry at the switch
2) When controller decides an action on a packet, installs in switch
3) Decision/flow table entry is cached
You can turn a switch into a firewall
in less than 40 lines of Python code
