CompTIA A+ Core Certification: A Simple Guide To Networking - Network Configuration Concepts

220-1101: Objective 2.6: Compare and contrast common network configuration concepts.
Computer network technologies evolve at a rapid pace, and keeping track of all the different technologies and protocols can be daunting. Still, a fundamental understanding of communication processes and network configuration concepts is essential for a computer technician. This will become even more true as people increase their computer use for communication and as the number of devices talking to each other grows exponentially. 

Domain names are how humans identify web server destinations on the Web. For example, NYT.com, US.gov, and Alaska.edu are all domain names that point to useful websites. Computers, however, use IP addresses, so domain names have to be translated, or mapped, to computer-friendly network addresses. This is not unlike the contacts list on your phone that maps people’s names to their phone numbers.

Computers and other devices use the Domain Name System (DNS) to map names to addresses on the Internet. Servers throughout the Internet track names and addresses. When a user types in www.cisco.com, the DNS protocol sends out messages asking for the network address of cisco.com. A DNS server that knows then responds with the address.

This process is often called resolving IP addresses. It generates a lot of traffic on the Web, and DNS traffic can sometimes be generated by viruses that target a server and cause so much traffic with DNS requests that the server shuts down.
 

DNS stores 32-bit IPv4 address data in A records. DNS accesses A records when resolving IPv4 address requests. IPv6 addresses are bigger (128 bits), and DNS stores them in AAAA records.
Handling email traffic on the Web is a daunting task. One function of DNS is to efficiently map email addresses to the destination email servers. It does this by sending a DNS mail exchange (MX) record that directs email to a mail server. The MX record works with SMTP, the standard mail protocol, to determine mail priority and other settings.
Text (TXT) records enable administrators to enter common text explanations into DNS that usually describe domain ownership or other information. TXT records are also used to counter email spam.

Other DNS tools that can protect email from spam follow:
DomainKeys Identified Mail (DKIM): A process that enables a receiving mail system to make sure that the message was authorized by the sending party and was not used for spam or phishing.
Sender Policy Framework (SPF): A tool that lets domain owners list the IP addresses that are authorized to send mail, to control spam.
Domain-based Message Authentication, Reporting, and Conformance (DMARC): A mail authentication process that builds on DKIM and SPF to further enhance security from fraudulent spam.

When a device is configured to receive an IP address dynamically, a DHCP server leases the first available IP address from a specific pool or range of IP addresses. A device is leased an IP address for a certain amount of time and can renew a leased IP address before the lease expires. This process is known as a DHCP leasing. If the lease expires, the device must request an IP address again. The purpose of using a lease is to ensure that any unused IP addresses are put back into the pool of available addresses and can be leased to another device. Otherwise, the pool of addresses could become quickly depleted.
 

Configuring a DHCP reservation with a specific address from the DHCP pool of addresses is possible. This is a permanent lease that is assigned to a DHCP client. It is similar to a static address, in that it doesn’t change, but it is configured into the DHCP server and the address is from the range of addresses that DHCP gives out to clients.
 

A DHCP scope is a pool or range of IP addresses that the DHCP server can assign or lease to devices. Generally, a scope is a single pool of IP addresses that are assigned to devices on a specific network. In some cases, multiple scopes are configured within the DHCP server to assign to devices on different networks.

VLAN
A virtual local area network (VLAN) is a group of computers on a local area network (LAN) that are configured to behave as if they have their own separate LAN. Usually LANs are separated by a router, but a switch might have the capability to group ports together to behave like a LAN inside the switch. Because the LAN exists in software configuration instead of in hardware, it is considered a VLAN. For example, if a LAN of 10 computers is divided evenly into VLAN 1 and VLAN 2, the computers in VLAN 2 will be able to communicate among themselves, but not with any hosts on VLAN 1. The hosts in each VLAN will even have IP addresses on different networks, and communicating between VLANs will require the services of a router.

VPN
A virtual private network (VPN) is a private (secure) network connection that is carried by an insecure public network, such as the Internet. A VPN connection requires a VPN server at the remote site and a VPN client at the client site. VPN traffic between client and server is encrypted and encapsulated into packets suitable for transmission over the network. VPNs can be used in place of leased lines for connections between locations and for telecommuting workers.
 

The most common types of VPNs are PPTP and L2TP/IPsec VPNs. PPTP uses 128-bit encryption. L2TP combined with IPsec (L2TP/IPsec) uses 256-bit encryption.
Remember that a VPN extends a LAN by establishing a remote connection, a connection tunnel, using a public network such as the Internet. Common VPN implementations include site to site, host to site, and host to host.