West Chapter 3

Four Addressing Methods

- Application Layer FQDNs - Transport Layer Port Numbers - Network Layer IP Address - Data Link Layer MAC Address

OUI (Organizationally Unique Identifier) (block ID) (company-ID)

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.

Resolver

A DNS client that requests information from DNS name servers.

Recursive Query

A DNS query that demands a resolution or the response that the information can't be found.

Iterative Queries

A DNS query that does not demand a resolution, which means the server provides the information only if it already has that information available.

Root Servers

A DNS server maintained by ICANN and IANA that is an authority on how to contact the top-level domains, such as those ending with .com, .edu, .net, .us, and so on. ICANN oversees the operation of 13 clusters of root servers around the world.

Port Address Translation (PAT)

A form of address translation that assigns a separate TCP port number to each ongoing conversation, or session, between a local host and an Internet host.

Command-Line Interface (CLI)

A graphic-free user interface, such as the Command Prompt program in Windows, where technicians can enter commands more quickly and with more flexibility than in a GUI (graphical user interface) environment.

NetBIOS over TCP/IP (NetBT) (NetBIOS)

A protocol that runs in the Session and Transport layers of the OSI model and associates NetBIOS names with workstations. NetBIOS allows old applications designed for out-of-date NetBIOS networks to work on TCP/IP networks.

MGCP (Media Gateway Control Protocol)

A protocol used for communication between media gateway controllers and media gateways.

Hosts File

A text file that associates TCP/IP host names with IP addresses. On a UNIX- or Linux-based computer, hosts is found in the /etc directory. On a Windows-based computer, it is found in the %systemroot%\system32\ drivers\etc folder.

CNAME (Canonical Name) Record

A type of DNS data record that holds alternative names for a host.

MX (Mail Exchanger) Record

A type of DNS data record that identifies a mail server and that is used for email traffic.

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.

Unicast Address

A type of IPv6 address that represents a single node on a network.

Static Network Address Translation (SNAT)

A type of address translation in which a gateway assigns the same public IP address to a host each time it makes a request to access the Internet.

Dynamic Network Address Translation (DNAT)

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.

Extension Identifier (Device ID)

A unique set of characters assigned to each NIC by its manufacturer. In the traditional, 48-bit physical addressing scheme, the extension identifier is 24 bits long. In EUI-64, the extension identifier is 40 bits long.

Samba

An open source software package that provides complete Windows-style file- and printer-sharing capabilities.

Tunneling

The process of encapsulating one type of protocol in another. Tunneling is the way in which higher-layer data is transported over VPNs by Layer 2 protocols.

Address Translation

The process of substituting a private IP address used by computers on a private network with the public IP address of a gateway device or router when these computers need access to other networks or the Internet.

Open Source

The term that describes software whose code is publicly available for use and modification.

Vim Text Editor

The text editing utility in Linux that allows a technician to make changes to text files, such as when editing the IP address range for a DHCP server.

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 TCP/IP addressing and domain name information in the Windows client operating systems.

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.

Elevated Command Prompt Window

A command prompt window with administrative privileges.

Loopback Interface

A computer's connection with itself.

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.

Distributed Database Model

A database model in which data is distributed over multiple servers. In the case of DNS, for example, the records for host names and IP addresses are stored on thousands of servers around the globe so that DNS will not fail catastrophically if one or a handful of servers experience errors.

DNS Cache

A database on a computer that stores information about IP addresses and their associated host names. DNS caches can exist on clients as well as on name servers.

Firewall

A device (either a router or a computer running special software) that selectively filters or blocks traffic between networks.

CIFS (Common Internet File System)

A file access protocol. CIFS runs over TCP/IP and is the cross-platform version of SMB used between Windows, UNIX, and other operating systems.

DNS (Domain Name System or Domain Name Service)

A hierarchical way of tracking domain names and their addresses, devised in the mid-1980s. The DNS database does not rely on one file or even one server, but rather is distributed over several key computers across the Internet to prevent catastrophic failure if one or a few computers go down. DNS is a TCP/IP service that belongs to the Application layer of the OSI model.

Fully Qualified Domain Name (FQDN)

A host name plus domain name that uniquely identifies a computer or location on a network.

Class A

A license for a single octet in an IPv4 address range. For example, the Class A license for 119 would acquire 119.0.0.0 through 119.255.255.255 IP addresses.

Class C

A license for the first three octets in an IPv4 address range. For example, the Class C license for 200.80.15 would acquire 200.80.15.0 through 200.80.15.255 IP addresses.

Class B

A license for the first two octets in an IPv4 address range. For example, the Class B license for 150.100 would acquire 150.100.0.0 through 150.100.255.255 IP addresses.

Socket

A logical address consisting of a host's IP address and the port number of an application running on the host with a colon separating the two values. For example, if a host has an IP address of 10.43.3.87, the socket address for Telnet running on that host is 10.43.3.87:23.

Multicasting

A means of transmission in which one device sends data to a specific group of devices (not necessarily the entire network segment) in a point-to-multipoint fashion.

Split-Horizon DNS

A method for preventing routing loops. This Layer 3 technology is employed by distance-vector routing protocols to ensure that a router knows which of its interfaces received a routing update so the router will not retransmit that same update back on the same interface.

DDNS (Dynamic DNS)

A method of dynamically updating DNS records for a host. DDNS monitoring software reports IP address changes to the DDNS service, which automatically updates DNS records.

Interface

A network connection made by a node or host on a network.

Alias

A nickname for a host.

Caching-Only Server

A nonauthoritative name server that exists merely to resolve names for clients. When it receives a request for information that is not stored in its DNS cache, it will then query the company's authoritative name server.

Internet Assigned Numbers Authority (IANA)

A nonprofit, U.S. 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.

Hexidecimal Number (Hex Number)

A number written in the base 16 numbering system, which uses the 16 numerals 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, and F.

Private Port

A port assigned by a network administrator that is different from the well-known port number normally used for that service.

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. SMB was first used by earlier Windows OSs for file sharing on a network. UNIX uses a version of SMB in its Samba software. The cross-platform version of SMB used between Windows, UNIX, and other operating systems is called the CIFS (Common Internet File System) protocol.

Signaling Protocol

A protocol that makes an initial connection between hosts but that does not actually participate in data exchange.

DNS Servers

A server that contains a database of TCP/IP host names and their associated IP addresses. A DNS server supplies a resolver with the requested information. If it cannot resolve the IP address, the query passes to a higher-level DNS server.

Automatic Private IP Address (APIPA)

A service available on computers running one of the Windows operating systems that automatically assigns the computer's network interface a link-local IP address. In IPv4, this address is in the range of 169.254.0.1 through 169.254.255.254. IPv6 does not use APIPA, but a similar address type, the unicast link-local address with the prefix FE80::/10, is used instead.

SIP (Session Initiation Protocol)

A set of Application layer signaling and control protocols for multiservice, packet-based networks. SIP is used to make an initial connection between hosts for transferring multimedia data.

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.

Bit

A single pulse in the digital encoding system that can have one of only two values: 0 or 1.

Packet Analyzer (Protocol Analyzer)

A software package or hardware-based tool that can capture and analyze data on a network. Protocol analyzers are more sophisticated than network monitoring tools, as they can typically interpret data up to Layer 7 of the OSI model.

Internet Protocol version 6 (IPv6)

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.

Reservation

A static IP address assigned by DHCP.

Octal Number System (Base 8 Number System)

A system founded on using eight numbers (0 through 7) to encode information.

Binary Number System (Base 2 Number System)

A system that uses 1s and 0s to encode information.

Network Address Translation (NAT)

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.

Zone Files

A text file associated with a DNS zone that contains resource records identifying domains and their IP addresses.

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. Using DHCP to assign IP addresses can nearly eliminate duplicate-addressing problems.

SNMP (Simple Network Management Protocol)

An Application layer protocol in the TCP/IP suite used to monitor and manage devices on a network.

Loopback Address

An IP address reserved for communicating from a node to itself, used mostly for troubleshooting purposes. The IPv4 loopback address is always cited as 127.0.0.1, and the IPv6 loopback address is ::1.

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. BOOTP and DHCP are two ways of assigning dynamic IP addresses.

Static IP Address

An IP address that is manually assigned to a device and remains constant until it is manually changed.

Public IP Addresses

An IP address that is valid for use on public networks, such as the Internet. An organization assigns its hosts public addresses from the range of addresses assigned to it by Internet numbering authorities.

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. DNS servers and Web servers are typically placed in the DMZ.

Split DNS

An implementation of DNS where internal and external DNS queries are handled by different DNS servers or by a single DNS server that is specially configured to keep internal and external DNS zones separate.

Link (Local Link)

Any local area network (LAN) bounded by routers.

Private IP Address

IP addresses that can be used on a private network but not on the Internet. IEEE recommends the following IP address ranges for private use: 10.0.0.0 through 10.255.255.255; 172.16.0.0 through 172.31.255.255; and 192.168.0.0 through 192.168.255.255.

Zone Transfer

In DNS, the act of copying a primary name server's zone file to the secondary name server to ensure that both contain the same information.

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 portion and what portion is the host portion.

Time to Live Field

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.

Authoritative Servers

The authority on computer names and their IP addresses for computers in their domains.

Name Servers

See DNS server.

Computer Name

See FQDN.

Fully Qualified Host Name

See FQDN.

Host Table

See hosts file.

Dynamic Port

TCP/IP ports in the range of 49,152 through 65,535, which are open for use without requiring administrative privileges on a host or approval from IANA.

Internet Protocol version 4 (IPv4)

The Internet Protocol standard released in the 1980s and still commonly used on modern networks. It specifies 32-bit addresses composed of four octets.

Well-Known Ports

The TCP/IP port numbers 0 to 1023, so named because they were long ago assigned by Internet authorities to popular services (for example, FTP and Telnet), and are, therefore, well known and frequently used.

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.

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 Internet IP addresses and their associated names distributed over DNS name servers worldwide.

Host Name

The first part of an FQDN, such as www or ftp, which identifies the individual computer on the network.

Default Gateway

The gateway device that nodes on the network turn to first for access to the outside world.

Interface ID

The last 64 bits, or four blocks, of an IPv6 address that uniquely identify the interface on the local link.

Top-Level Domain (TLD)

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.

BIND (Berkeley Internet Name Domain)

The most popular DNS server software. BIND is free, open source software that runs on Linux, UNIX, and Windows platforms.

Internet Corporation for Assigned Names and Numbers (ICANN)

The nonprofit corporation currently designated by the U.S. government to maintain and assign IP addresses.

DHCP Scope

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.

Neighbors

Two or more nodes on the same link.