Chapter 9. Software-Defined Networking and Networking for Containers

Question 1

What problem does the virtualization of the network solve?

Answer 1

• high demands that traditional networks cannot cope with (mobile devices, cloud computing,…)
• similiar flexibility needed for the connection of devices, applications, VMs, containers
• can be achieved by virtualization of network

Question 2

What does Software-Defined Networking (SDN) allow?

Answer 2

• decoupling of the network control layer from the traffic forwarding layer
• allows SDN to program the control layer and to create custom rules in order to meet new networking requirements

Question 3

What planes are categorized in networking?

Answer 3

• Data Plane
• Control Plane
• Management Plane

Question 4

What is the Data Plane in networking responsible for?

Answer 4

• responsible for handling data packets and applying actions to them based on rules which we program into lookup-tables
• also called Forwarding plane

Question 5

What is the Control Plane in networking responsible for?

Answer 5

• tasked with calculating and programming the actions for the Data Plane
• here are forwarding decisions made and where services such as Quality of Service (QoS) and VLANs are implemented

Question 6

What is the Management Plane in networking responsible for?

Answer 6

• is the place where we can configure, monitor and manage network devices

Question 7

What kind of activities has every network device to perform?

Answer 7

• Ingress and egress packets
• Collect, process and manage network information
• monitor and manage the network

Question 8

Where is the network device activity of “Ingress and egress packets” performed?
What is part of these plane activities?

Answer 8

• at the lowest layer
• which decides what to do with packets based on forwarding tables
• these activities are mapped as Data plane activities
• all routers, switches, modems, etc are part of this plane

Question 9

Where is the network device activity of “Collect, process and manage the network information” performed?
What is part of these plane activities?

Answer 9

• the network device makes forwarding decisions by collecting, processing and managing the network information, which the Data plane follows
• these activities are mapped by the Control plane
• some protocols which run on Control plane are routing and adjacent device discovery

Question 10

Where is the network device activity of “Monitor and manage the network” performed?
What is part of these plane activities?

Answer 10

• using tools available in the Management plane we can interact with the network device to configure it and monitor it with tools like Simple Network Management Protocol (SNMP)

Question 11

How does networking work in Software-defined networking (SDN)?

Answer 11

• decoupling of Control Plane and Data Plane
• Control Plane has centralized view of the overall network, allows it to create forwarding tables of interest
• these tables are then submitted to Data Plane to manage network traffic
• Control Plane has well defined APIs that receive requests from applications to configure the network
• after preparing the desired state, the Control plane communicates that to the Data plane, using a well defined Protocol like Open Flow

Question 12

What is important in regards to communication with containers?

Answer 12

• containers need to be able to communicate with other containers on the same or different hosts
• network namespaces are used to isolate the network from one container to another on the host system
• network namespaces can be shared between containers

Question 13

As an example how does the container communication on hosts work?

Answer 13

• on single host, using virtual Ethernet feature with Linux brdiging, a virtual network interface can be given to each container while assinging an IP address
• with tools like Macvlan and IPVlan each container can be configured to have a unique worldwide routable IP address

Question 14

How can multi-host networking be achieved with containers?

Answer 14

• usually by using some sort of Overlay network driver
• that usually encapsulates the Layer 2 traffic to a higher layer
• examples: Docker Overlay Driver, Flannel, and Weave

Question 15

Which standards have been proposed for container networking?

Answer 15

• Container Network Model (CNM)
• Container Networking Interface (CNI)

Question 16

What is the Container Network Model?

Answer 16

• main driver: Docker Inc.
• uses libnetwork project
• standardized build process through three main components

Question 17

What are the three main components for the Container Network Model?

Answer 17

• a network sandbox
• one or multiple endpoints
• one or more networks

Question 18

What is the Container Network Interface? (CNI)

Answer 18

• Cloud Native Computing Foundation project (CNCF)
• consists of specifications and libraries for writing plugins to configure network interfaces in Linux containers

Question 19

What is the Container Network Interface limited to?
Who uses this model?

Answer 19

• providing network connectivity of containers and removing allocated resources when the containers are deleted
• used by projects like Kubernetes, OpenShift, Cloud Foundry

Question 20

What is Service discovery, especially in the container context?

Answer 20

• mechanism that enables processes and services to find each other
• context container: provides mapping between a server name and its ip-address, which can change in its lifetime

Question 21

What are the steps for service discovery?

Answer 21

• Registration
• Lookup

Question 22

How does the Registration step for service discovery work?

Answer 22

• when container starts, the scheduler registers the container name to the container IP mapping in a key-value store like etcd or Consul
• if a container stops or restarts the scheduler updated the mapping accordingly

Question 23

How does the LookUp step for service discovery work?

Answer 23

• Services and applications use LookUp to retrieve the IP address of a container so that they can connect to it
• generally supported by Domain Name Server (DNS), which is local to the environment
• DNS resolves the requests by looking at the entries in the key-value store, which is used in Registration