305-300 Exam Dumps : LPIC-3: Virtualization and Containerization - Exam 305, version 3.0

The purpose of a .dockerignore file is to specify files that Docker does not submit to the Docker daemon when building a Docker image. A .dockerignore file is a text file that contains a list of files or directories that should be excluded from the build context, which is the set of files and folders that are available for use in a Dockerfile. By using a .dockerignore file, you can avoid sending files or directories that are large, contain sensitive information, or are irrelevant to the Docker image to the daemon, which can improve the efficiency and security of the build process. The other options are incorrect because they do not describe the function of a .dockerignore file. Option A is wrong because a .dockerignore file does not affect the files existing in a Docker image, but only the files sent to the daemon during the build. Option C is wrong because a .dockerignore file does not exist in the root file system of containers, but in the same directory as the Dockerfile. Option D is wrong because a .dockerignore file does not affect the volumes that Docker attaches to a container, but only the files included in the build context. Option E is wrong because a .dockerignore file does not affect the parts of a Dockerfile that are executed, but only the files available for use in a Dockerfile. References:

What are .dockerignore files, and why you should use them?

Dockerfile reference | Docker Docs

How to use .dockerignore and its importance - Shisho Cloud

LXC implements system containers, which are a type of operating-system-level virtualization. System containers allow running multiple isolated Linux systems on a single Linux control host, using a single Linux kernel. System containers share the same kernel with the host and each other, but have their own file system, libraries, andprocesses. System containers are different from application containers, which are designed to run a single application or service in an isolated environment. Application containers are usually smaller and more portable than system containers, but also more dependent on the host kernel and libraries. Hardware containers, CPU emulation, and paravirtualization are not related to LXC, as they are different kinds of virtualization methods that involve hardware abstraction, instruction translation, or modification of the guest operating system. References:

1: LXC - Wikipedia

2: Linux Virtualization : Linux Containers (lxc) - GeeksforGeeks

3: Features - Proxmox Virtual Environment

Libvirt supports creating and managing various types of virtual networks that can be used to connect virtual machines to each other or to the external network. One of the common types of virtual networks is the NAT-based network, which uses network address translation (NAT) to allow virtual machines to access the outside world through the host’s network interface. By default, libvirt creates a NAT-based network called ‘default’ when it is installed and started. This network appears as a standard Linux bridge device on the host system, named virbr0. The bridge device has an IP address of 192.168.122.1/24 and acts as a gateway and a DHCP server for the virtual machines connected to it. The bridge device also has iptables rules to forward and masquerade the traffic from and to the virtual machines. The virtual machines connected to the ‘default’ network have their own IP addresses in the 192.168.122.0/24 range and their own MAC addresses generated by libvirt. The virtual machines can communicate with each other, with the host, and with the external network through the bridge device and the NAT mechanism12.

The other statements in the question are false regarding networking with libvirt. Libvirt’s network functionality is not limited to connecting virtual machines to a physical network interface of the host system. Libvirt can also create isolated networks that do not have any connection to the outside world, or routed networks that use static routes to connect virtual machines to the external network without NAT3. Libvirt does not assign the same MAC address to all virtual machines and isolate their network interfaces at the link layer. Libvirt assigns a unique MAC address to each virtual machine and allows them to communicate with each other at the network layer4. Libvirt does not require a dedicated network interface that may not be used by the host system. Libvirt can share the host’s network interface with the virtual machines using NAT or bridging, or it can pass a physical network interface to a virtual machine exclusively using PCI passthrough5. Libvirt does not support exactly one virtual network and connect all virtual machines to it. Libvirt supports creating and managing multiple virtual networks with different names and configurations, and connecting virtual machines to different networks according to their needs6. References:

libvirt: Virtual Networking

libvirt: NAT forwarding (aka “virtual networks”)

libvirt: Routed network

libvirt: MAC address

libvirt: PCI passthrough of host network devices

[libvirt: Network XML format]