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CS6520 Test 3 > Lesson 9 - Software Defined Networking > Flashcards

Lesson 9 - Software Defined Networking Flashcards

1
Q

3 sections of the course

A

1: Basic building blocks of the internet
2: How networks deal with large amounts of network traffic
3 (this one): How network operators manage their networks

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2
Q

3 topics of this section, which introduce us to the forefront of networking research

A

SDN
Traffic Engineering
Network Security

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3
Q

What is network management?

A

The process of configuring the network to achieve a variety of tasks, including:

            * Balancing traffic load across the network
            * Achieving various security goals
            * Satisfying business relationships that may exist between the network being configured and neighboring networks, such as the network’s upstream ISP
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4
Q

Network configuration (very important) mistakes can lead to:

A
  • Persistent oscillation (routers can’t agree on a route to a destination)
  • Loops (packets get stuck in between 2 or more routers and never actually make it to the destination
  • Partitions: the network is split into 2 or more segments that are not connected
  • Black holes: Packets reach a router that does not know what to do with it, and drops it, as opposed to sending it along to its destination
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5
Q

SDN provides operators with what 3 things?

A
  1. Network-wide views
    - Of both topology and traffic
  2. Ability to satisfy network-level objectives, including load balancing, security, and other goals.
  3. Direct control, in particular:
    - Rather than requiring network operators to configure each device individually with indirect configuration, SDN allows an operator to write a control program that directly affects/manipulates the data plane.

*allows a network operator to express network-level objective and direct control from a logically centralized controller.

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6
Q

To make network operations easier, routers should:

A
  • Forward packets (since router hardware is specialized to forward traffic at very high rates)
  • Collect measurements (such as traffic statistics and topology information
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7
Q

There’s no reason that a router should have to:

A

Compute routes. Although conventionally routing has operated as a distributed computation of forwarding tables, the computation doesn’t inherently need to run on the routers. It can be logically-centralized and be controlled from a centralized control program

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8
Q

What are the 2 defining features of SDN?

A

Logically-centralized control

Network-wide control

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9
Q

SDN’s simple goal is to

A

Remove routing from the routers and perform that routing computation at a logically centralized controller.

*It has also evolved to incorporate a much broader range of controls than simply routing decisions

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10
Q

Today’s networks have 2 functions

A
  • Data plane, whose task it is to forward packets to their ultimate destination.
    • Need a “state” in each router, known as a routing table, which allow it to make decisions to forward packets.
  • Control plane: job is to compute the routing tables.
      * In conventional networks today, the control and data plane both run on the routers that are distributed across the network
  * In an SDN, the control plane runs in a logically-centralized controller.
      * Additionally, the controller typically controls multiple routers across the network, and often, the control program exerts control over all of the routers in the network, thus facilitating network-wide control.
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11
Q

The refactoring from SDN allows us to…

A

Move from a network where devices are vertically integrated (making it very tough to innovate), to a network where the devices have open interfaces that can be controlled by software, thus allowing for much more rapid innovation.

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12
Q

RCP

A

Routing Control Platform

Previous to 2004:
-Configuration was distributed, leading to buggy or unpredictable behavior.

Around 2004, we had the idea to control the network from a logically centralized, high-level program.
-The logically-centralized controller focused on the Border Gateway Protocol (BGP), and was called the Routing Control Platform (RCP).

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13
Q

2005 generalized RCP

A
  • Decision plane: Computed the forwarding state for devices in the network
  • Data plane: Forwarded traffic based on decisions made by the Decision plane
  • Dissemination/discovery planes: provide the decision plane the information it needs to compute the forwarding state which ultimately gets pushed to the data plane.
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14
Q

OpenFlow

A

Around 2008: Concepts effectively hit the mainstream through a protocol called OpenFlow

  • OpenFlow’s intellectual roots are with the RCP and 4D, but it was made practical when merchant silicon vendor opened their API’s, so that switch chip-sets could be controlled from software. So suddenly, there was an abundance of cheap switches that were built based on open chipsets that could be controlled from software.
    • This development effectively allowed us to decouple the control plane and the data plane in commodity switching hardware.
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15
Q

Advantages of SDN over conventional networks

A
  1. Coordination: easier to coordinate behavior among a network of devices
  2. Evolve: Behavior of the network is easier to evolve
  3. Reasoning: Easier to reason about
    * These characteristics are all rooted in the fact that the control plane is separate from the data plane. This allows us to apply conventional CS techniques to old networking problems.
    * Before, it was difficult to reason about or debug a network’s behavior.
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16
Q

SDN’s infrastructure

A
  • Control plane: typically a software program written in a high-level language, such as Python or C
    * Affects the forwarding state that’s in the switch using control commands.
    * OpenFlow is one standard that defines a set of control commands by which a controller can control the behavior of one or more switches.

-Data plane: typically programmable hardware, and is controlled by the control plane.

17
Q

Which of the following are examples of control plane operations?

  • Computing a forwarding path that satisfies a high-level policy
  • Computing a shortest-path routing tree
  • Rate-limiting traffic
  • Load balancing traffic based on hash of source IP
  • Authenticate a user’s device based on MAC address
A
  • Computing a forwarding path that satisfies a high-level policy
  • Computing a shortest-path routing tree
  • Authenticate a user’s device based on MAC address
18
Q

Control Plane

A

The logic that controls forwarding behavior

    * Examples:
        * Routing protocols
        * Logic for configuring network middle boxes
    * Routing protocol might compute shortest paths over a topology, but ultimately the results of such computations must be installed in switches that actually do the forwarding
19
Q

Data Plane

A

Actual forwarding of traffic according to the forwarding logic from the Control Plane

    * Examples:
        * Forwarding packets at the IP layer, doing things like switching at layer 2
    * The act of actually taking a packet at an input port and forwarding it at an output port is a data plane function
20
Q

Why separate Control and Data planes?

A
  1. Independent evolution and development
    * Plus, SW control of the network can evolve independently of the network hardware
  2. Opportunity to control the network behavior from a high-level software program
    * In theory, this allows network operators to debug and check behavior more easily than in the status quo where network behavior is determined by distributed low-level configuration across 100s of switches and routers
21
Q

The separation of data and control provides opportunities:

A
  • Data centers, by facilitating network tasks such as VM migration to adapt to fluctuating network demands
  • In routing: it provides more control over decision logic
  • Enterprise: provides the ability to write security applications such as applications that manage network access control
  • Research: allows us to virtualize the network so that research networks and experimental protocols can coexist with production networks on the same underlying network hardware
22
Q

What are reasons for separating data and control planes?

  • No single point of failure
  • Ability to scale to much larger networks
  • Independent evolution of data and control planes
  • Separating vendor hardware from control logic
  • Easier reasoning about network behavior
A
  • Independent evolution of data and control planes
  • Separating vendor hardware from control logic
  • Easier reasoning about network behavior
23
Q

How does control/data separation make managing data centers easier?

  • Monitoring/control of routes from a central point
  • Migrating VMs without renumbering host addresses
  • Fewer switches
  • Auto load balance
A
  • Monitoring/control of routes from a central point

- Migrating VMs without renumbering host addresses

24
Q

2 fundamental challenges with SDN

A
  • Scalability
    * A single control element might be responsible for many forwarding elements (maybe hundreds to thousands of switches)
  • Consistency
    * For redundancy and reliability, typically we want to replicate the controller. So, while it’s logically centralized physically there may be many replicas. In such a scenario, we need to make sure different controller replicas see the same view of the network, so that they make consistent decisions when they’re installing state in the data plane

-A final challenge, also worth mentioning, is Security/Robustness: want to make sure that the network continues to function correctly in the event that a controller replica fails or is compromised

25
Q

What are ways to cope with scalability challenges?

  • Eliminate redundant data structures
  • Only perform control-plane operations for a limited # of hops
  • Send all traffic to controller
  • Cache forwarding decisions in switches
  • Run multiple controllers
A
  • Eliminate redundant data structures
  • Only perform control-plane operations for a limited # of hops
  • Cache forwarding decisions in switches
  • Run multiple controllers
26
Q

NOX

A
  • NOX was a first generation OpenFlow controller
    * It’s open-source, stable, and widely used
  • 2 flavors of NOX:
    * “Classic”
    * Written in C++ and Python and is no longer supported
    * “New NOX”
    * Written in C++ only
    * Codebase is fast, clean, and well-supported
    * More info is available at noxrepo.org
    • The basic abstraction that NOX supports is a switch control abstraction, where OpenFlow is the prevailing protocol
    • Control is defined at the granularity of flows, which are defined by a 10-tuple in the original OpenFlow specification
    • Controller may make different decisions for packets that belong to different parts of flow space, or packets that match different subnets of the fields defined by a flow

***Watch this lecture again

27
Q

Basic programmatic interface for the NOX controller is based on

A

Events

-Controller knows how to process different types of events, such as a switch joining or leaving, packet in/rec’d event, various statistics

28
Q

NOX provides good performance but requires

A

The programmer to understand and be comfortable with the facilities and semantics of low-level OpenFlow commands

29
Q

POX

A
  • NOX requires the programmer to write the control application in C++, which can be slow for development and debugging
    * To address the shortcomings in development with C++, POX was developed
    * POX is:
    * Widely-used
    * Maintained
    * Supported
    * Easy to use
    * Easy to read and write control programs
    * Since it’s implemented in Python, the performance of POX is not as good as the performance of NOX
30
Q

When to use POX?

  • Class Projet
  • Large internet data center
  • University research
A
  • Class Projet

- University research

31
Q

Ryu

A
  • Open-source Python controller
    * Supports OpenFlow 1.0, 1.2, 1.3, as well as the Nicira extensions
    * Works with OpenStack
    * Support for OpenStack and later versions of OpenFlow are advantages over other SDN controllers
    * It does NOT perform as well as other SDN controllers, because it was created in Python
32
Q

Floodlight

A
  • Written in java
    * Supports OF 1.0
    * Fork from the earlier “Beacon” controller
    * Advantages:
    * Good documentation
    * Integration with REST API
    * Good performance
    * Disadvantage:
    * Steep learning curve. Use it if you already know Java, if you need production level performance and support, and will use the REST API to interact with the controller
  • ** All of the 4 controllers shown are still relatively hard to use because they entail interacting directly with OpenFlow flow table modifications, which operate at a very low level of matching on flows and performing specific actions.
  • ** As we’ll see, it’s possible to develop programming languages on top of these controllers that make it much easier for a network operator to reason about network behavior
33
Q

If all of the fields are specified for forwarding out of a particular output port, then we have

A

flow switching behavior

34
Q

If all of the flow specifications are wild carded except for, say, the source MAC address, then we have

A

a firewall

35
Q

Constructing a firewall

A

Building a hash table that maps switch and source MAC address to a True or False value, depending on whether traffic should be forwarded or dropped

36
Q

Caching

A
  1. Packets only reach controller if no flow table entry at switch
  2. When controller decides on action, installs in switch
  3. Decision/flow table entry is cached
37
Q

OpenFlow makes modifying forwarding behavior easy because forwarding decisions are based on…

A

Matches on the OpenFlow 10-tuple

CS6520 Test 3 (6 decks)

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