Chapter 12 Network Configuration

What is a host?

A host is any device that communicates with another device.

What is a network packet?

Packets are used to send network communications between hosts. The data delivery is broken down into smaller chunks (packets), that allow for much more efficient delivery.

What is SOA?

This is the Start of Authority. These records indicate the primary server for the domain... ...Example: $host -t SOA example.com Additionally, a comprehensive list of DNS information can be found using -a option.

What is the file that holds the location of the DNS server(s)?

/etc/resolv.conf

What is the primary IPv4 configuration file?

/etc/sysconfig/network-scripts/ifcfg-eth0

What is a client?

A client is a host that is accessing a server.

What is a network?

A network is a collection of two or more hosts that are able to communicate with each other.

$netstat can also be used to display open ports.

A port is a unique number that is associated with a service provided by a host. If the port is open, then the service is available for other hosts. -tln option will display list of all currently open ports. "LISTENing" means the port is open.

What is a router?

A router is a "gateway" and it is a machine that connects hosts from one network to another network.

What is a server?

A server is a host that provides a service to another host or client, i.e. a web server stores, processes, and delivers web pages.

What must each host have in order to access the internet?

Each host must have a unique IP address! In the IPv4 environment, there is a technical limit of about 4.3 billion IP addresses.

What is a hostname?

Each host on a network could have its own hostname. Hostnames are translated into IP addresses before the network packet is sent on the network.

Okay, let's talk more about IP addresses

Hosts will use the IP address to "address" network packets to the destination machine. The network packet will also include the "return address" of the sending machine.

What protocol do roughly 98-99% of devices on a network still use?

IPv4! But how is this even possible? It's possible due to two reasons primarily. 1. The invention of NAT 2. Porting issues

What are porting issues?

Porting is switching over from one technology to another. IPv6 has a lot of great new features but all of the hosts need to be able to utilize these features. Getting everyone on the internet (or even just some) to make these changes poses a challenge.

What is TCP/IP?

TCP is transmission control protocol and IP is internet protocol This is just a fancy name for a collection of protocols (protocol = set of rules) that are used to define how network communication should take place between hosts. This is the most often utilized collection of protocols.

What does the $netstat command do?

This can be used to display information about network connections as well as display the routing table similar to route command. TX-OK and TX-ERR are important to make note of with this command as a high amount of TX-ERR statistics can indicate a problem on the network. -i option to display statistics and -r option to display routing.

What does the $ifconfig command do?

This command is "interface configuration" and it is used to display network configuration info.

What does $route do?

This command shows where network packages are sent.

What does the $host command do?

This command works with DNS to associate a hostname with an IP address. It can also determine the hostname if the IP address is known instead.

What does /etc/hosts file contain?

This contains a table of hostnames to IP addresses. It can be used to supplement a DNS server.

What does the /etc/nsswitch/conf file contain?

This file can be used to modify where hostname lookups occur.

What does the /etc/sysconfig/network file contain?

This file contains the network setting that can determine if networking is turned on (yes) or off (no). The hostname setting defines the local machine's hostname.

What is DNS?

This is Domain Name Server. It is the service of translating domain names into IP addresses. Hostnames are translated into IP addresses prior to the network packet being sent on the network.

What is DHCP?

This is Dynamic Host Configuration Protocol. It is used to assign hosts with hostnames, IP addresses, and other network related information. DHCP defines how network information is assigned to client hosts and the DHCP server is the machine that provides this information.

What the heck is NAT?

This is Network Address Translation. A group of hosts are placed into a private network with no direct access to the Internet. A router is given a single IP address to access the internet and then the group of hosts on the private network share this single IP address.

What is a network mask?

This is a number system that can be used to define which IP addresses are considered to be within a single network. Networks have to be clearly defined.

What does $ping do?

This is a tool used to determine whether or not another machine is "reachable"

What is a RSA key fingerprint?

This is a unique code for the machine you are logging into. The RSA key fingerprint will be stored on your local system and designed to aid in future login attempts. If you receive an error related to the RSA key fingerprint, it could be caused by a man-in-the-middle attack or simply the system was recently reinstalled and now has a new RSA key. You can remove the ~/.ssh/known-hosts file from your local system (or just remove the entry for that one machine) and try to connect again. When you want to return to your local machine, run the $exit command. This will logout and close connection to "test".

what is a IP address?

This is a unique number assigned to a host on a network. Hosts use these numbers to "address" network communication.

What is IPv4?

This is internet protocol version 4. It is a total of four 8-bit numbers used to define the address. (8-bit = numbers from 0 to 255) i.e. the address 192.168.10.120 is considered a 32-bit address because 4 times 8-bit = 32=bit.

What is IPv6?

This is internet protocol version 6! It was officially "created" in 1998. The addresses for IPv6 are much larger 128-bit addresses. This new IPv6 has many more advanced features that address some of IPv4's limitations, including better speed, more advanced package management and more efficient data transportation.

What does CNAME stand for?

This is the canonical name--aka alias. Example. $host -t CNAME example.com ... there is no CNAME record for ....

What is ethernet?

This is the most common way to physically connect hosts into a network. These cables are connected to network cards that support ethernet connections. The most common speeds are 10Mbps/100Mbps/1000Mbps.

What is a denial of service attack?

This is when a server is overwhelmed by the amount of information it receives, i.e. it is overwhelmed by a massive number of network packets.

What does the $dig command do?

This performs queries on the DNS server to determine if the information needed is available on the server. $dig example.com This will determine the IP address of the host. If none of the DNS servers have the requested information, you will receive an error message: "connection timed out; no servers could be reached"

What is a ssh command?

This will allow you to connect to another machine across the network, log in and then perform tasks on the remote machine. If you want to use a different username to login, follow the syntax "username@hostname"

What about $ip addresses show?

This will reveal your machine IP address.

Let's talk about DNS once more....

When a computer tries to access www.example.com, the IP address is not known for this website and the computer relies on DNS to associate an IP address with the URL or hostname request. It is common to have multiple name server settings in the event that one DNS server isn't responding.

What needs to be done after making configuration changes?

You either need to reboot the machine or run a command as the administrator to make the changes take effect.