Week2_les1

Question 1

Welke vijf fundamentele kenmerken van SDN worden er in het boek genoemd?

Answer 1

1: plane separation , 2: a simplified device , 3: centralized control , 4: network automation and virtualization , and 5: openness .

Question 2

Geef een beschrijving van reden(en) waarom de forwarding en control plane bij SDN zouden moeten worden gescheiden.

Answer 2

In deze paragraaf wordt dat niet expliciet besproken, maar het idee is dat door het scheiden van beide lagen o.a. nieuwe applicaties/tools kunnen worden worden ontworpen, dat de complexiteit wordt verminderd, er centraal beheer mogelijk wordt en dat de prestaties en veiligheid zouden moeten verbeteren.

Question 3

Welke vier mogelijke forwarding beslissingen kunnen er door de controle plane (volgens het boek!) worden genomen?

Answer 3

Forward, drop, consume en replicate Geef een beschrijving van de forwarding beslissingen die door een normale switch (via ASICs) wordt genomen. A packet may be dropped due to buffer overflow conditions or due to specific filtering resulting from a QoS rate-limiting function.

Question 4

Waar bevindt zich de logic en de gebruikte algoritmes om forwarding beslissingen te nemen.

Answer 4

Op de router, switch of bijvoorbeeld firewall zelf.

Question 5

De slimheid van een apparaat wordt bij SDN verplaatst van de control plane naar de ..?

Answer 5

Naar een controller / server.

Question 6

Welke redenen worden in het boek genoemd waarom het zinvol is om netwerkapparatuur te vereenvoudigen?

Answer 6

Complexiteit (vele regels aan code) verminderen en een controller het overzicht van het netwerk te geven en daarmee het netwerk aan te sturen.

Question 7

Wat wordt er verstaan onder distributed state, forwarding and configuration?

Answer 7

Het geven van controle en besluitvorming aan de controller

Question 8

Wat wordt er verstaan onder northbound en southbound (API)?

Answer 8

Met Northbound wordt bedoeld: de mogelijkheden om de controller te beheren en/of te programmeren. Dit vereist meestal een gebruikersinteractie. Southbound APIs/protocollen: communiceren met de hardware om deze (dynamisch) te configureren.

Question 9

Wat wordt er verstaan onder een flow en een flow table?

Answer 9

A flow describes a set of packets transferred from one network endpoint (or set of endpoints) to another endpoint(or set of endpoints). One set of rules describes the actions that the device should take for all packets belonging to that flow. A flow is unidirectional in that packets flowing between the same two endpoints in the opposite direction could each constitute a separate flow. Flows are represented on a device as a flow entry. A flow table resides on the network device and consists of a series of flow entries and the actions to perform when a packet matching that flow arrives at the device. When the SDN device receives a packet it consults its flow tables in search of a match. These flow tables had been constructed previously when the controller downloaded appropriate flow rules to the device. If the SDN device finds a match, it takes the appropriate configured action, which usually entails forwarding the packet. If it does not f ind a match, the switch can either drop the packet or pass it to the controller, depending on the version of OpenFlow and the configuration of the switch.

Question 10

Wat zal er met de data gebeuren als er geen match in de flow table wordt gevonden?

Answer 10

Dan zal het verzoek naar de controller worden verzonden. De controller kan dan mogelijk de flows aanpassen.

Question 11

Welke beschrijving van een SDN-controller worden op pagina 65 gegeven?

Answer 11

The SDN controller is responsible for abstracting the network of SDN devices it controls and presenting an abstraction of these network resources to the SDN applications running above. The controller allows the SDN application to define flows on devices and to help the application to respond to packets which are forwarded to the controller by the SDN devices.

Question 12

Op welke laag of lagen van het OSI-model werken SDN-applicaties?

Answer 12

De applicatie zit zelf meestal op laag7, maar zal aanpassingen maken op laag 2, 3 en 4. (de vierde laag wordt in het boek niet genoemd, maar het is mogelijk om aanpassingen te maken op bijvoorbeeld TCP en UDP)

Question 13

Wat wordt er verstaan onder een proactive flow?

Answer 13

Proactive flows are established by the application; typically the application will set these flows when the application starts up, and the flows will persist until some configuration change is made. Noem een voorbeeld van een reactive flow. There are also reactive flows that are defined or modified as a result of stimuli from sources others than packets from the controller. For example, the controller can insert flows reactively in response to other data sources such as Intrusion Detection Systems (IDS) or the NetFlow traffic analyzer.

Question 14

Een SDN-apparaat heeft drie functionele lagen. Welke drie zijn dat?

Answer 14

De controller, de abstraction layer en de packet processing function.

Question 15

Wat is een Flow Table?

Answer 15

Een flow table is de functionele data structure van een SDN device. Data wordt met de entries in de flow table vergeleken. Elke entry bestaat uit een match field en een action. Match fields kunnen een wildcard bevatten om de flow voor meerdere pakketten te laten gelden.

Question 16

Wat is Policy-Based Routing (PBR) en waarom zit dat meestal in TCAM?

Answer 16

PBR (zie later in de cursus!) is het zoeken naar de longest match. TCAM is sneller.

Question 17

Wat is een ODM?

Answer 17

De twee SDN implementaties zijn Open vSwitch (OVS) en OpenFLow. Whitbox switches (Original Device Manufacture (ODM) is hardware zonder naam.

Question 18

Welke plek in het netwerk krijgt een SDN-device met een hoge mate van flow granularity?

Answer 18

De edge van het netwerk. 4.4 SDN Controller

Question 19

Welke mogelijkheden worden door een SDN-Controller geboden?

Answer 19

Overzicht van het netwerk, implementatie van Policy decisions, controle van de netwerkinfrastructuur en het bieden van een northbound API voor applicaties. Naast openflow kan Cisco CLI en SNMP ook als southbound protocol worden gebruikt. Openflow en Openv vSwitch Database Management Protocol (OVSDB) zijn open source varianten.

Question 20

Wat zijn de core features van de SDN-controller?

Answer 20

4 De controller zorgt voor een abstractie. Hierdoor hoeft de applicatie niet te weten hoe de hardware moet worden aangesproken. End-user Device Discovery : Discovery of end-user devices, such as laptops, desktops, printers, mobile devices, etc. Network Device Discovery : Discovery of network devices which comprise the infrastructure of the network, such as switches, routers, and wireless access points. Network Device Topology Management : Maintain information about the interconnection details of the network devices to each other, and to the end-user devices to which they are directly attached. Flow Management : Maintain a database of the flows being managed by the controller and perform all necessary coordination with the devices to ensure synchronization of the device flow entries with that database. The core functions of the controller are device and topology discovery and tracking, flow management, device management and statistics tracking

Question 21

Wat wordt er bedoeld met de SDN Controller interfaces?

Answer 21

Een Northbound API/interface om met de controller te communiceren. Een southbound interface om met de hardwar te communiceren.

Question 22

Op welk(e) punt(en) verschillende controllers?

Answer 22

Protocollen (o.a. REST) en programmeertaal als Java, REST, Python en Ruby

Question 23

Wat zijn de voor- en nadelen van proprietary controllers?

Answer 23

Werkt met specifieke hardware, maar zal meestal niet direct de laatste specificaties /versies ondersteunen. ODL en ONOS worden als meest bruikbare open source controllers gezien.

Question 24

Welke potentiele problemen met een SDN-controller worden er in het boek (blz. 75) genoemd?

Answer 24

Nieuwe technologien hebben altijd aanloop problemen. Commercile controllers zullen waarschijnlijk beter schaalbaar zijn. Vernieuwingen moeten worden goedgekeurd door bijvoorbeeld de ONF. Verder mogelijk problemen met: cordinatie tussen applicaties, het gebrek aan gestandaardiseerde northbound APIs en flow prioritization. 4.5 SDN Applications

Question 25

Wat hebben de meeste SDN-controllers met elkaar gemeen?

Answer 25

Er worden applicaties gebruikt om via de Northbound interface met de controller te communiceren. Through this API the applications are able to: (1) configure the flows to route packets through the best path between two endpoints; (2) balance traffic loads across multiple paths or destined to a set of endpoints; (3) react to changes in the network topology such as link failures and the addition of new devices and paths, and (4) redirect traffic for purposes of inspection, authentication, segregation, and similar security-related tasks.

Question 26

Welke verantwoordelijkheden worden er genoemd in het kader van SDN-applicaties?

Answer 26

The general responsibility of an SDN application is to perform whatever function for which it was designed, be it load-balancing, firewalling, or some other operation. Once the controller has finished initializing devices and has reported the network topology to the application, the application spends most of its processing time responding to events. While the core functionality of the application will vary from one application to another, application behavior is driven by events coming from the controller as well as external inputs. External inputs could include network monitoring systems, such as Netflow, IDS, or BGP peers. 4.6 Alternate SDN Methods

Question 27

Welke alternatieven categorien zijn er voor de originele definitie van SDN die wordt aangeduid als OpenSDN?

Answer 27

we define here two alternate categories of SDN implementations, SDN via APIs and SDN via Hypervisor-Based Overlay Networks . The first of these consists of employing functions that exist on networking devices that can be invoked remotely, typically via traditional methods, such as SNMP, CLI, or NETCONF. Alternatively, newer mechanisms such as RESTful APIs may be used. In SDN via Hypervisor-Based Overlay Networks the details of the underlying network infrastructure are not relevant. Virtualized overlay networks are instantiated across the top of the physical network. We make the distinction that the overlays be hypervisor-based since network overlays exist in other, non hypervisor-based forms as well. One early example of this sort of network virtualization is VLAN technology. Another type of overlay network that is not related to our use of the term are P2P/Overlay networks such as Napster and BitTorrent. Geef een beschrijving van SDN via Device APIs. In SDN via Device APIs , the strategy is to provide a richer set of control points on the devices, so that centrally located software can manipulate those devices and provide the intelligent and predictable behavior that is expected in an SDN-controlled network. Consequently, many vendors offer SDN solutions by improving the means of affecting configuration changes on their network devices.

Question 28

Wat wordt er verstaan onder REST, I2RS en RIB?

Answer 28

REST has become the dominant method of making API calls across networks for computational tasks. REST uses HyperText Transfer Protocol (HTTP), the protocol commonly used to pass web traffic. RESTful APIs are simple and extensible and have the advantage of using a standard TCP port and, thus, require no special firewall configuration to permit the API calls to pass through firewalls. Interface to the Routing System (I2RS) [ 23 ] I2RS provides an interface between routing protocols and the Routing Information Base (RIB). The four key drivers inspiring this new protocol are: The need for an interface that is programmatic, asynchronous, and offers fast, interactive access for atomic operations. To provide access to structured routing information and state that is frequently not directly configurable or modeled in existing implementations or configuration protocols. To provide the ability for network management and other applications to subscribe to structured, filterable even t notifications from the routing system. To facilitate extensibility and provide standard data-models to be used by network applications.

Question 29

Wat zijn NETCONF, YANG en RESTCONF?

Answer 29

NETCONF is one of the device management and configuration protocols most favored by vendors and customers today. It is used especially in higher-level devices such as core routers. These devices expose their configurable information via data models defined using the YANG data definition language. (NETCONF and YANG will be discussed in greater detail in Section 6.2.2 .) In our context of SDN via Controller APIs, the application typically makes RESTCONF requests to the controller. RESTCONF is a protocol wherein NETCONF requests are bundled in easier-to-use REST messages. The controller in turn translates the RESTCONF request into the NETCONF protocol, with the contents of the request remaining fundamentally the same.

Question 30

Wat wordt er verstaan onder imperative en declarative?

Answer 30

imperative: Imperative systems and APIs require the user to input exactly how to do a particular task. Declarative: Declarative systems and APIs request the user to input exactly what is to be accomplished. It is the responsibility of the system to determine how to do it.

Question 31

Wat zijn de voor- en nadelen van SDN via APIs?

Answer 31

There are a number of benefits of SDN via APIs. One distinct advantage of this approach is that, because it uses legacy management interfaces, it therefore works with legacy switches. Thus, this solution does not require upgrading to OpenFlow-enabled switches. Another benefit of this approach is that it allows for some improvement in agility and automation. These APIs also make it easier to write software such as orchestration tools which can respond quickly and automatically to changes in the network (e.g., the movement of a virtual machine in a data center). A third advantage is that it allows for some amount of centralized control of the devices in the network. Therefore, it is possible to build an SDN solution using the provided APIs on the distributed network devices. Finally, there is potential for increased openness in the SDN via APIs approach. Although the individual interfaces may be proprietary to individual vendors, when they are exposed to the applications, they are made open for exploitation by applications. The degree of openness will vary from one NEM to another. Of course, the API-based SDN methods have their limitations. First, in some cases there is no controller at all . The network programmer needs to interact directly with each switch. Second, even when there is a controller, it may not provide an abstract, network-wide view to the programmer. This is certainly true when dealing with NETCONF-based APIs on the controller. In these situations, the programmer needs to think in terms of individual switches. Geef een beschrijving van Overlaying. Another more innovative alternate SDN method is what we refer to as Hypervisor-Based Overlay networks. Under this concept the current physical network is left as it is, with networking devices and their configurations remaining unchanged. Above that network, however, hypervisor-based virtualized networks are erected. The systems at the edges of the network interact with these virtual networks, which obscure the details of the physical network from the devices that connect to the overlays.

Question 32

Waar staat de afkorting MD-SAL voor?

Answer 32

Model-driven service abstraction layer. Dit is de laag tussen de applicaties aan de noordkant en de hardware aan de zuidkant.

Question 33

Wat zijn de doelen van MD-SAL?

Answer 33

Abstraction : Earlier versions of ODL resulted in every southbound protocol having its own protocol-specific set of APIs. This clearly is not desirable for application developers, having to develop against varying APIs for multiple different protocols. MD-SAL permits communication to devices only through models, thus yielding an abstraction that provides protocol-independent APIs for application developers to use. Standardized Communication : When an MD-SAL module is created, APIs for the module are automatically generated by tools included within the MD-SAL environment. Thus, these APIs (both RESTful and internal) are more standardized than would otherwise be true if they were created ad hoc by human developers. Significantly, these APIs are generated automatically by the build framework, and thus require no extra design or implementation effort by the API developer. This facilitates easier intermodule and interapplication communication. Microservices : Microservices are a software architecture style in which complex applications are composed of small, independent processes communicating with each other using standardized APIs. MD-SAL facilitates such an environment in ODL through the use of YANG models to define every service. Hence every MD-SAL application is a service with its own auto-generated APIs. Welk protocol zal door de Network providers, volgens het boek, worden gebruikt NETCONF en BGP Monitoring Protocol (BMP)

Question 34

Wat zijn de drie kenmerken van intents based applications?

Answer 34

Abstraction : The goal of an SDN controller, as with operating systems in general, is to abstract the details of the hardware below from the application running above. Declarative : Specifying what to do, rather than how to do it, is a characteristic of declarative systems. Protocol-agnostic : An abstract declarative interface hides details of how the network programming occurs, allowing different protocols to be used in different situations. In het boek worden twee additionele Application models genoemd.

Question 35

Wat is het verschil tussen een imperative en een declarative system?

Answer 35

An imperative system requires that it be told exactly how to do something. The net result of all the hows is that the system will achieve the what that was intended in the first place. A declarative system needs only be told what needs to be done; the system itself figures out how to accomplish the goal.

Question 36

Wat voor een type SDN controller is bijvoorbeeld APIC-em van Cisco?

Answer 36

Policy-level API / controller

Question 37

wat zijn de kenmerken van de external application focus?

Answer 37

ExternalSDNapplicationscanbewritteninmanydifferentprogramminglanguagesincluding Python, Ruby, PERL, and even scripting languages. ExternalSDNapplicationscanrunonthesamesystemasthecontroller,onadifferentbut geographically local system, on a remote system, or even in the cloud. ExternalSDNapplicationsgenerallyhaveareducedimpactontheoperationofthecontroller(e.g., internal applications can cause failures or bottlenecks on the controller).

Question 38

Wat zijn de kenmerken van de programmeertaal P4?

Answer 38

Language : The language itself is declarative, and is syntactically similar to C. Matches : Matching tables define against what the incoming packets will be compared. Actions : Action tables define what should be done to the packet after a match has occurred. Compile-time vs. Run-time : The language is intended to be compiled into run-time format for efficient execution.

Question 39

Bij welk type controller/proces kom je de programmeertaal P4 tegen?

Answer 39

Policy-based routing (ACLs, forwarding).

Question 40

Benoem de verschillen en overeenkomsten tussen een SDN-software en hardware switch.

Answer 40

Functionaliteiten komen overeen, zo hebben beide flow tabellen. Als de snelheid hoog moet zijn (100Gbs) dan is hardware noodzakelijk. Software SDN is sterk beter geworden. Software toepassingen zijn minder kwetsbaar voor resource beperkingen als processing power en memory size. Software toepassingen zijn instaat om meer flows en flexibiliteit daarvan te gebruiken. Hardware heeft een beperkt aantal flow entries. Software based SDN gaat meestal via hypervisors. Hardware werkt met Content-addressavle Memories (CAM) of TCAM