How SDN works? need help answering this question

Question

1-In a SDN using the OpenFlow protocol, packet forwarding rules are stored in the packet switch's

a- forwarding table 

b- switch table        

c- arp table

d- flow table

e- None of the above

2- In a SDN, entries in a packet switch's flow table are managed by

a) the packet switch itself

b) a network administrator

c) a remote controller

d) neighboring switches

e) None of the above

3- What is the defacto standard protocol for inter-AS routing for the Internet?

Answer 1

The key to answering the SDN related questions (1 and 2) is to understand what OpenFlow is:

Firstly, OpenFlow is not synonymous with SDN. SDN is more than a split control/data plane. But OpenFlow is used as part of many SDN solutions.

OpenFlow is a network stack designed to manage and direct traffic among routers and switches from various vendors. It separates the programming of routers and switches from underlying hardware. (different vendors do have varying levels of support for OpenFlow.)

The technology consists of three parts: flow tables installed on switches, a controller and a the OpenFlow protocol for the controller to talk securely with switches.

Flow tables are set up on switches. Controllers talk to the switches via the OpenFlow protocol and impose policies on flows. As a result it is the controller that can add, update, and delete flow entries in flow tables, both reactively and proactively.

In an OpenFlow network, each OpenFlow switch contains at least 1 flow table (usually more) and a set of flow entries within that table. These flow entries contain match fields, counters and instructions to apply to matched packets. If a matching entry is found, the instructions associated with the specific flow entry are executed. If no match is found in a flow table, the outcome depends on the configuration of the Table-miss flow entry. The Table-miss flow entry is the last in the table. It’s basically a catch-all, and the actions to be taken depend on how you configure it. You can forward the packet to the controller over the OpenFlow Channel, or you could drop the packet, or continue with the next flow table.

Hope that helps