Essential Services Flashcards by Kathrin Brunner

What’s the purpose of a server?

The purpose of a server is usually to provide services to clients (“to serve” others).

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Which two types of clients do you know?

Clients and servers can be internal clients (in, e.g., a corporate network) or external (internet).

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What does IP stand for?

Internet Protocol

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What are Routers/Gateways used for?

Routers/Gateways are used to connect different networks in that they route packets originating from the source network to the destination network based on their destination IP address.

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What are NAT Routers? What’s special about them?

NAT Routers, allow a single external IP address to be used by many private addresses.

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Why are IPv4 addresses still in use?

A lot of devices still lack support for IPv6

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How are the parts of IPv6 addresses separated?

By :

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What does DNS stand for?

domain name system

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What does the DNS do?

As IP addresses, consisting of several numbers, are hard to remember, the domain name system (DNS) has been put in place. Its purpose is the translation of names to IP addresses and back.

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How does the communication between client and DNS server work?

The client queries the DNS server to resolve the name, that is it asks the DNS server for the IP address associated with a given name. The DNS servers responds with an IP address and the client can connect via this IP address.

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How many ports are there per IP address?

65535 (different doors)

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What are well-known ports?

Standardised ports, whose port number is associated with a known service. (service = server)

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What’s the job of the web server?

The web server is used, as the name suggests, to serve web pages.

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How are web pages requested and transferred?

With the HTTP protocol (hyper text transfer protocol)

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Name a popular web server

Apache 2

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What does SSL stand for?

secure socket layer

Name SSL libraries

OpenSSL or GnuTLS

Why is configuration split across multiple files?

For better separation

What are the most important configurations?

ServerAdmin
Name (and e-mail address) of the server administrator
ServerName
Name of the server, usually fully qualified domain name (FQDN)
DocumentRoot
Where to look for documents to serve
SSLEngine
Enable/disable encryption (SSL)

What is a Virtual Host?

One Apache server can be configured to serve multiple domains and IP addresses. A Virtual Host is used to serve different domains or subdomains on the same IP address. Apache then decides upon connecting, based on the name, which virtual host has to respond (Name-based Virtual Hosts). Each Virtual Host can have its own set of Apache options defined.

How can you extend Apache’s functionality of a basic server?

By using modules

Name some Modules

Server Sided Scripts (PHP, WSGI, CGI, …)
Encryption Support (SSL)
Database Access (MySQL, PostgreSQL, SQLite, …)
File Serving Capabilities (WebDAV)
Proxy Support

What is PHP?

A very powerful and common scripting language is PHP, the Hypertext Pre-Processor

How and where are PHP scripts executed?

All PHP scripts are executed on the server and can run directly within Apache using the PHP interpreter (provided as an Apache Module).

How are PHP scripts identified?

PHP scripts are identified by their file extension, nowadays most of the time simply .php

Which applications are written in PHP?

Many modern web applications are written in PHP, examples include Webmail, Content Management Systems, Web Forms, Wiki Systems, etc.

What can you find in /etc/php?

System-wide configuration for PHP and an Apache-specific configuration file.

What's SSH standard port?

What can you do against SSH attackers?

It is good practice to change the port to a higher, unused number. However, this only reduces the amount of attacks, but is in no way a security concept (security by obscurity).

How and why can you compare SSH and VPN?

SSH provides the ability to tunnel about anything over its encrypted channel. It thus provides nearly the capabilities of a fully-fledged virtual private network (VPN) solution.

What is a Secure Shell Daemon?

Remote console login services are provided by the Secure Shell Daemon - ssh. It allows the user to remotely connect to a server and gain access to the console via an encrypted channel. Authentication can either be done via password or public key or even a combination thereof. SSH also provides a secure way to copy files, without capabilities to list directory contents (scp). On the other hand, a secure implementation similar to FTP is availabe (sftp).

Where lies the configuration of SSH?

The configuration of SSH is split into server and client side configuration files. Both files rely under the /etc/ssh directory and are even named very similarily.

What is the SMTP Server?

The SMTP Server (Simple Mail Transfer Protocol) is used for sending an E-Mail from one machine to another (for example Postfix).

What does IMAP stand for?

Internet Message Access Protocol

What does POP stand for?

Post Office Protocol

How does E-Mail communication work?

The SMTP Server sends an E-Mail from one machine to another. The E-Mail is then stored by the handling (receiving) SMTP service into the user’s inbox. An IMAP or POP server enable the receiver to check for and retrieve the message.

Which ports do you need to run a secure, modern E-Mail system?

Ports 25, 143 and 110