Computer Network Unit 3
broadcast
A message that is read by every node on a network.
DHCP reservation
An IP address that is set aside by a DHCP server for a specific network client, which is identified by its MAC address.
dynamic port
Number assigned by a client or server as the need arises.
Octets
One of 4 bytes that are separated by periods and together make up an IPv4 address.
default gateway
The gateway device that nodes on the network turn to first for access to the outside world.
node ID
The portion of an IP address that identifies the node on a network
forward zone
A DNS lookup file that holds A records.
iterative query
A DNS query that does not demand a resolution, which means the server provides the information only if it already has that information available.
Extension identifier
A unique set of characters assigned to each NIC by its manufacturer
extension identifier
A unique set of characters assigned to each NIC by its manufacturer.
dig (domain information groper)
A utility available on Linux and macOS that provides more detailed domain information than nslookup. Use dig to query DNS nameservers for information about host addresses and other DNS records.
dynamic IP address
An IP address that is assigned to a device upon request and may change when the DHCP lease expires or is terminated.
static IP address
An IP address that is manually assigned to a device and remains constant until it is manually changed.
classful addressing
An IP addressing convention that adheres to network class distinctions, in which the first 8 bits of a Class A address, the first 16 bits of a Class B address, and the first 24 bits of a Class C address are used for network information.
global address
An IPv6 address that can be routed on the Internet. These addresses are similar to public IPv4 addresses. Most global addresses begin with the prefix 2000::/3, although other prefixes are being released.
NS (Name Server) record
A DNS lookup file that indicates the authoritative name server for a domain. It's mostly used for delegating subdomains to other name servers.
recursive query
A DNS query that demands a resolution or the response that the information can't be found.
WSL (Windows Subsystem for Linux)
A Linux shell CLI in Windows that allows users to interact with underlying Windows functions and system files
SPF (Sender Policy Framework)SPF (Sender Policy Framework)
A validation system that helps fight spam by identifying the email servers allowed to send email on behalf of a domain.
LDAPS (Lightweight Directory Access Protocol over SSL
A version of LDAP that uses SSL to encrypt its communications with network directories and clients
device ID or extension identifier
67, 68
OUI (organizationally unique identifier)
A 24-bit character sequence assigned by IEEE that appears at the beginning of a network interface's physical address and identifies the NIC's manufacturer
elevated Command Prompt
A Command Prompt window with administrative privileges.
resolvers
A DNS client that requests information from DNS name servers
reverse zone
A DNS lookup file that holds A records where the IP addresses must be stored in reverse— with the last octet listed first—plus the domain .in-addr.arpa. For example, the IP address 1.2.3.4 would be stored in a PTR record as 4.3.2.1.in-addr.arpa.
IANA (Internet Assigned Numbers Authority)
A nonprofit, US government-funded group that was established at the University of Southern California and charged with managing IP address allocation and the Domain Name System. The oversight for many of IANA's functions was given to ICANN in 1998; however, IANA continues to perform Internet addressing and Domain Name System administration.
DNS zone
A portion of the DNS namespace for which one organization is assigned authority to manage.
SMB (Server Message Block)
A protocol for communications and resource access between systems, such as clients and servers
caching DNS server
A server that accesses public DNS data and caches the DNS information it collects.
DMZ (demilitarized zone)
An area on the perimeter of a network that is surrounded by two firewalls—an external firewall that is more porous to allow more types of access, and an internal firewall that is more hardened to provide greater protection to the internal network.
DKIM (DomainKeys Identified Mail)
An authentication method that uses encryption to verify the domain name of an email's sender.
process
An instance of running a computer application or service
ifconfig
An interface configuration and management utility used with UNIX and Linux systems.
session
An ongoing conversation between two hosts.
forwarding DNS server
An optional server that receives queries from local clients but doesn't work to resolve the queries.
name servers
Computers that hold these databases, organized in a hierarchical structure
Open source
Software whose code is publicly available for use and modification.
registered ports
The TCP/IP ports in the range of 1024 to 49,151. These ports can be used by network users and processes that are not considered standard processes. Default assignments of these ports must be registered with IANA.
well-known ports
The TCP/IP ports numbered 0 to 1023, so named because they were long ago assigned by Internet authorities to popular services and are, therefore, well known and frequently used.
primary DNS server
The authoritative name server for an organization, which holds the authoritative DNS database for the organization's zones. This server is contacted by clients, both local and over the Internet, to resolve DNS queries for the organization's domains.
secondary DNS server
The backup authoritative name server for an organization.
APIPA (Automatic Private IP Addressing)
A service available on Windows computers that automatically assigns the computer's NIC a link-local IPv4 address in the range of 169.254.0.1 through 169.254.255.254.
anycast address
A type of IPv6 address that represents a group of interfaces, any one of which (and usually the first available of which) can accept a transmission. At this time, anycast addresses are not designed to be assigned to hosts, such as servers or workstations, but rather to routers.
dual stacked
A type of network that supports both IPv4 and IPv6 traffic.
DHCPv6
The version of DHCP used with IPv6.
FQDN (Fully Qualified Domain Name)
A host name plus domain name that uniquely identifies a computer or location on a network
canonical name
The true name of a server, such as www.example.com, as opposed to one of many alias names a server might have, such as ns1.example.com.
ipconfig
The utility used to display and alter TCP/IP addressing and domain name information in the Windows client operating systems
-incorrect netmask -incorrect gateway -duplicate IP address -names not resolving
What are some common configuration errors?
TFTP (Trivial File Transfer Protocol
A TCP/IP Application layer protocol that is seldom used by humans. Computers commonly use it as they are booting up to request configuration files from another computer on the local network. Unlike FTP, TFTP relies on UDP at the Transport layer using port 69
ping (Packet Internet Groper)
A TCP/IP troubleshooting utility that can verify TCP/IP is installed, bound to the NIC, configured correctly, and communicating with the network. Ping uses ICMP to send echo request and echo reply messages.
nslookup (name space lookup)
A TCP/IP utility that allows a technician to query the DNS database from any computer on the network and find the host name of a network node by specifying its IP address, or vice versa. This ability is useful for verifying that a host is configured correctly and for troubleshooting DNS resolution problems.
gateway
A computer, router, or other device that a host uses to access another network. Gateways perform connectivity, session management, and data translation, so they must operate at multiple layers of the OSI model.
ICMP (Internet Control Message Protocol)
A core protocol in the TCP/IP suite that notifies the sender when something has gone wrong in the transmission process and packets were not delivered.
firewall
A device (either a router, a dedicated device, or a computer running special software) that selectively filters or blocks traffic between networks.
TTL (Time to Live)
A field that indicates the maximum duration that an IPv4 packet can remain on the network before it is discarded. Although this field was originally meant to represent units of time, on modern networks it represents the number of times a packet can still be forwarded by a router, or the maximum number of router hops remaining.
CLI (command-line interface)
A graphic-free user interface, such as the Command Prompt application in Windows, where technicians can enter commands more quickly and with more flexibility than in a GUI (graphical user interface) environment
DNS (Domain Name System or Domain Name Service)
A hierarchical way of tracking domain names and their addresses, devised in the mid-1980s.
FQDN (fully qualified domain name)
A host name plus domain name that uniquely identifies a computer or location on a network.
socket
A logical address consisting of a host's IP address and the port of an application running on the host with a colon separating the two values
interface
A network connection made by a node or host on a network
DHCP scope
A shortage of available IP addresses on a network so that no new clients can connect to the network.
exhausted DHCP scope
A shortage of available IP addresses on a network so that no new clients can connect to the network.
SIP (Session Initiation Protocol
A signaling protocol that is used to make an initial connection between hosts but that does not participate in data transfer during the session
H.323
A signaling protocol used to make a connection between hosts prior to communicating multimedia data. H.323 has largely been replaced by SIP, which is easier to use
NTP (Network Time Protocol
A simple Application layer protocol in the TCP/IP suite used to synchronize the clocks of computers on a network. NTP depends on UDP for Transport layer services
subnet
A smaller network within a larger network in which all nodes share a network addressing component and a fixed amount of bandwidth
IPv6(Internet Protocol version 6
A standard for IP addressing that is gradually replacing the current IPv4. Most notably, IPv6 uses a newer, more efficient header in its packets and allows for 128-bit source and destination IP addresses, which are usually written as eight blocks of hexadecimal numbers, such as 2001:0DB8:0B80:0000:0000:00D3:9C5A:00CC.
LDAP (Lightweight Directory Access Protocol
A standard protocol for accessing network directories
address translation
A technique in which IP addresses used on a private network are assigned a public IP address by a gateway when accessing a public network.
CNAME (Canonical Name) record
A type of DNS data record that holds alternative names for a host.
TXT (Text) record
A type of DNS data record that holds any type of free-form text. It might contain text designed to be read by humans regarding network, server, or accounting issues.
MX (Mail Exchanger) record
A type of DNS data record that identifies a mail server and that is used for email traffic.
SRV (Service) record
A type of DNS data record that identifies the hostname and port of a computer hosting a specific network service besides email, such as FTP or SIP.
PTR (Pointer) record
A type of DNS data record that is used for reverse lookups, to provide a host name when the IP address is known.
A (Address) record
A type of DNS data record that maps the IPv4 address of an Internet-connected device to its domain name.
AAAA (Address) record
A type of DNS data record that maps the IPv6 address of an Internet-connected device to its domain name. Pronounced "quad-A record."
DNAT (Destination Network Address Translation)
A type of address translation in which a gateway has a pool of public IP addresses that it is free to assign to a local host whenever the local host makes a request to access the Internet.
DHCP (Dynamic Host Configuration Protocol)
An Application layer protocol in the TCP/IP suite that manages the dynamic distribution of IP addresses on a network.
subnet mask
In IPv4 addressing, a 32-bit number that helps one computer find another by indicating what portion of an IP address is the network and subnet portion and what portion is the host portion
netmask
In IPv4 addressing, a 32-bit number that helps one computer find another by indicating what portion of an IP address is the network portion and what portion is the host portion.
broadcast domain
Logically grouped network nodes that can communicate directly via broadcast transmissions. By default, switches and repeating devices, such as hubs, extend broadcast domains. Routers and other Layer 3 devices separate broadcast domains.
private port
Number assigned by a network administrator that is different from the well-known port number for that service.
EUI-64 (Extended Unique Identifier-64)
The IEEE standard defining 64-bit physical addresses. In the EUI-64 scheme, the OUI portion of an address is 24 bits in length. A 40-bit extension identifier makes up the rest of the physical address, for a total of 64 bits.
IPv4 (Internet Protocol version 4)
The Internet Protocol standard released in the 1980s and still commonly used on modern networks. It specifies 32-bit addresses composed of four octet
authoritative server
The authority on computer names and their IP addresses for computers in their domains.
resource records
The element of a DNS database stored on a name server that contains information about TCP/IP host names and their addresses.
namespace
The entire collection of computer names and their associated IP addresses stored in databases on DNS name servers around the globe
Host name
The first part of an FQDN, such as www or ftp, which identifies the individual computer on the network
host name
The first part of an FQDN, such as www or ftp, which identifies the individual computer on the network.
-Data Link Layer MAC address -Network layer IP address -transport layer ports -application layer FQDNs, computer names, and host names
The four addressing methods
TLD (top-level domain)
The last part of an FQDN and the highest-level category used to distinguish domain names—for example, .org, .com, and .net. A TLD is also known as the domain suffix.
Domain name
The last two parts of an FQDN, such as mycompany.com. Usually, a domain name is associated with the company's name and its type of organization, such as a university or military unit
domain name
The last two parts of an FQDN, such as mycompany.com. Usually, a domain name is associated with the company's name and its type of organization, such as a university or military unit.
ICANN (Internet Corporation for Assigned Names and Numbers)
The nonprofit corporation currently designated by the US government to maintain and assign IP addresses
network ID
The portion of an IP address common to all nodes on the same network or subnet
host ID
The portion of an IP address that identifies the host on a network
DHCP pool
The predefined range of addresses that can be leased to any network device on a particular segment.
name resolution
The process of discovering the IP address of a host when the FQDN is known.
ICMPv6
The version of ICMP used with IPv6 networks. ICMPv6 performs the functions that ICMP, IGMP, and ARP perform in IPv4. It detects and reports data transmission errors, discovers other nodes on a network, and manages multicasting.
