Chapter 4

public address

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.

Bonjour

Apple's implementation of the Zeroconf group of protocols.

Routable

The protocols that can span more than one LAN because they carry Network layer and addressing information that can be interpreted by a router.

root server

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 root servers around the world.

Label

A character string that represents a domain (either top-level, second-level, or third-level).

ARP (Address Resolution Protocol)

A core protocol in the TCP/IP suite that belongs in the Network layer of the OSI model. ARP obtains the MAC (physical) address of a host, or node, and then creates a local database that maps the MAC address to the host's IP (logical) address.

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.

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 assigned to a specific process running on a computer. Some sockets are reserved for operating system functions.

dynamic ARP table entry

A record in an ARP table that is created when a client makes an ARP request that cannot be satisfied by data already in the ARP table.

static ARP table entry

A record in an ARP table that someone has manually entered using the ARP utility. Static ARP table entries remain the same until someone manually modifies them with the ARP utility.

host name

A symbolic name that describes a TCP/IP device.

Format Prefix

A variable-length field at the beginning of an IPv6 address that indicates what type of address it is (for example, unicast, anycast, or multicast).

TLD (top-level domain)

The highest-level category used to distinguish domain names—for example, .org, .com, and .net. A TLD is also known as the domain suffix.

Switch

The letters or words added to a command that allow you to customize a utility's output. Switches are usually preceded by a hyphen or forward slash character.

TCP (Transmission Control Protocol)

A core protocol of the TCP/IP suite. TCP belongs to the Transport layer and provides reliable data delivery services.

echo request

The request for a response generated when one device pings another device.

echo reply

The response signal sent by a device after another device pings it.

ICMP (Internet Control Message Protocol)

A core protocol in the TCP/IP suite that notifies the sender that something has gone wrong in the transmission process and that packets were not delivered.

alias

A nickname for a node's host name. Aliases can be specified in a local host file.

Ipconfig

The utility used to display TCP/IP addressing and domain name information in the Windows client operating systems.

ping6

The version of the PING utility used on Linux computers that run IPv6.

Ping

To send an echo request signal from one node on a TCP/IP-based network to another, using the PING utility. See also PING.

UDP (User Datagram Protocol)

A core protocol in the TCP/IP suite that sits in the Transport layer of the OSI model. UDP is a connectionless transport service.

anycast address

A type of address specified in IPv6 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.

Resolver

Any host on the Internet that needs to look up domain name information.

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, when combined with a device's IP address, indicates what kind of subnet the device belongs to.

Octet

One of the 4 bytes that are separated by periods and together make up an IPv4 address.

IP packet

The IP portion of a TCP/IP frame that acts as an envelope for data, holding information necessary for routers to transfer data between subnets.

Dynamic Ports

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.

country code

TLD A top-level domain that corresponds to a country. For example, the country code TLD for Canada is .ca, and the country code TLD for Japan is .jp.

resource record

The element of a DNS database stored on a name server that contains information about TCP/IP host names and their addresses.

dotted decimal notation

The shorthand convention used to represent IPv4 addresses and make them more easily readable by humans. In dotted decimal notation, a decimal number between 0 and 255 represents each binary octet. A period, or dot, separates each decimal.

Subprotocols

The specialized protocols that work together and belong to a protocol suite.

DHCPv6

The version of DHCP used with IPv6. DHCPv6 uses port number 546 for client-to-server communications and port number 547 for server-to-client communications.

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.

IPv4 IP 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 octets. It lacks the security, automatic addressing, and prioritization benefits of IPv6. It also suffers from a limited number of addresses, a problem that can be resolved by using IPv6 instead.

TFTP (Trivial File Transfer Protocol)

A TCP/IP Application layer protocol that enables file transfers between computers. Unlike FTP, TFTP relies on UDP at the Transport layer and does not require a user to log on to the remote host.

Ifconfig

A TCP/IP configuration and management utility used with UNIX and Linux systems.

IGMP (Internet Group Management Protocol or Internet Group Multicast Protocol)

A TCP/IP protocol used on IPv4 networks to manage multicast transmissions. Routers use IGMP to determine which nodes belong to a multicast group, and nodes use IGMP to join or leave a multicast group.

PING (Packet Internet Groper)

A TCP/IP troubleshooting utility that can verify that 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 that determine the validity of an IP address.

network class

A classification for TCP/IP-based networks that pertains to the network's potential size and is indicated by an IP address's network ID and subnet mask. Network Classes A, B, and C are commonly used by clients on LANs; network Classes D and E are reserved for special purposes.

Zeroconf (Zero configuration)

A collection of protocols that assigns link-local addresses, performs DNS functions, and discovers services, such as print services, available to the node.

ARP table

A database of records that maps MAC addresses to IP addresses. The ARP table is stored on a computer's hard disk where it is used by the ARP utility to supply the MAC addresses of network nodes, given their IP addresses.

Domain

A group of computers that belong to the same organization and have part of their IP addresses in common.

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.

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.

DDNS (Dynamic DNS)

A method of dynamically updating DNS records for a host. DDNS client computers are configured to notify a service provider when their IP addresses change, then the service provider propagates the DNS record change across the Internet automatically.

IPv6 (IP version 6)

A newer standard for IP addressing that is gradually replacing the current IPv4 (IP version 4). Most notably, IPv6 uses a newer, more efficient header in its packets and allows for 128-bit source and destination IP addresses. The use of longer addresses will allow for many more IP addresses to be in circulation. IPv6 also provides automatic addressing, better security, and prioritization features.

TTL (Time to Live)

A number that indicates the maximum duration that a 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 router hops a datagram has endured. The TTL for datagrams is variable and configurable, but is usually set at 32 or 64. Each time a datagram passes through a router, its TTL is reduced by 1.When a router receives a datagram with a TTL equal to 1, the router discards that datagram.

Subnet

A part of a network in which all nodes shares a network addressing component and a fixed amount of bandwidth.

DNS zone

A portion of the DNS namespace for which one organization is assigned authority to manage.

IPv4LL (IP version 4 Link Local)

A protocol that manages automatic address assignment among locally connected nodes. IPv4LL is part of the Zeroconf group of protocols.

Flow

A sequence of packets issued from one source to one or many destinations. Routers interpret flow information to ensure that packets belonging to the same transmission arrive together. Flow information may also help with traffic prioritization.

name server

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

DHCP server

A server that manages IP address assignment, maintaining information about which addresses are allowable, which are available, and which have already been associated with a host.

APIPA (Automatic Private IP Addressing)

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.

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.

TCP/IP (Transmission Control Protocol/Internet Protocol)

A suite of networking protocols that includes TCP, IP, UDP, and many others. TCP/IP provides the foundation for data exchange across the Internet.

Hop

A term used to describe each trip a unit of data takes from one connectivity device to another. Typically, hop is used in the context of router-to-router communications.

Telnet

A terminal emulation protocol used to log on to remote hosts using the TCP/IP protocol. Telnet resides in the Application layer of the OSI model.

zone file

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

host file

A text file that associates TCP/IP host names with IP addresses.

address resource record

A type of DNS data record that maps the IP address of an Internet-connected device to its domain name.

unicast address

A type of IPv6 address that represents a single interface on a device. An IPv6 unicast address begins with either FFC0 or FF80.

multicast address

A type of address in the IPv6 that represents multiple interfaces, often on multiple nodes. An IPv6 multicast address begins with the following hexadecimal field: FF0x, where x is a character that identifies the address's group scope.

dual-stack

A type of network that supports both IPv4 and IPv6 traffic.

Avahi

A version of Zeroconf available for use with the Linux operating system.

diskless workstation

A workstation that doesn't contain a hard disk, but instead relies on a small amount of read-only memory to connect to a network and to pick up its system files.

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.

FTP (File Transfer Protocol)

An Application layer protocol used to send and receive files via TCP/IP.

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, although in fact, transmitting to any IP address whose first octet is 127 will contact the originating device. In IPv6, the loopback address is represented as ::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.

link-local address

An IP address that is automatically assigned by an operating system to allow a node to communicate over its local subnet if a routable IP address is not available. ICANN has established the range of 169.254.0.0 through 169.254.254.255 as potential link-local IPv4 addresses. IPv6 link-local addresses begin with FE80.

static IP address

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

private address

An IP address used only on an organization's internal network. Certain IP address ranges are reserved for private addresses. Private addresses cannot be used to communicate over the Internet.

loopback test

An attempt to contact one's own machine for troubleshooting purposes. In TCP/IP-based networking, a loopback test can be performed by communicating with an IPv4 address that begins with an octet of 127. Usually, this means pinging the address 127.0.0.1.

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 are accessible to network users and processes that do not have special administrative privileges. Default assignments of these ports must be registered with IANA.

port number

The address on a host where an application makes itself available to incoming data.

Lease

The agreement between a DHCP server and client on how long the client can use a DHCP-assigned IP address. DHCP services can be configured to provide lease terms equal to any amount of time.

Namespace

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

TCP/IP core protocols

The major subprotocols of the TCP/IP suite, including IP, TCP, and UDP.

Hosts

The name of the host file used on UNIX, Linux, and Windows systems. 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.

network ID

The portion of an IP address common to all nodes on the same network or subnet.

DHCP scope

The predefined range of addresses that can be leased to any network device on a particular segment.

Subnetting

The process of subdividing a single class of network into multiple, smaller networks.

domain name

The symbolic name that identifies a domain. Usually, a domain name is associated with a company or other type of organization, such as a university or military unit.

DHCPv4

The version of DHCP used with IPv4. DHCPv4 uses port number 67 for client-to-server communications and port number 68 for server-to-client communications.

Internetwork

To traverse more than one LAN segment and more than one type of network through a router.