chapter 4 voc.

probe (1) A repeated trial message transmitted by the tracert and traceroute utilities to trigger routers along a route to return specific information about the route.

(2) A small electronic device that emits a tone when it detects electrical activity on a wire pair. When used in conjunction with a tone generator, it can help locate the termination of a wire pair. Also called a tone locator. (3) In 802.11 wireless networking, a type of frame issued by a station during active scanning to find nearby access points.

traceroute

A TCP/IP troubleshooting utility avail- able in Linux, UNIX, and macOS systems that sends UDP messages to a random port on the destination node to trace the path from one networked node to another, identifying all intermediate hops between the two nodes.

netstat

A TCP/IP troubleshooting utility that displays statistics and the state of current TCP/IP connections. It also displays ports, which can signal whether services are using the correct ports.

pathping

A Windows utility that combines the functionality of the tracert and ping utilities to provide deeper information about network issues along a route; similar to UNIX's mtr command.

tracert

A Windows utility that uses ICMP echo requests to trace the path from one networked node to another, identifying all intermediate hops between the two nodes.

default route

A backup route, usually to another router, used when a router cannot determine a path to a message's destination.

route command

A command-line tool that shows a host's routing table.

ARP (Address Resolution Protocol)

A core protocol in the TCP/IP suite that belongs in the Data Link layer of the OSI model. ARP works in conjunction with IPv4 to discover the MAC address of a node on the local network and to maintain a database that maps local IP addresses to MAC addresses.

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.

routing table

A database stored in a router's memory that maintains information about the location of hosts and best paths for forwarding packets to them.

tcpdump

A free, command-line packet sniffer utility that runs on Linux and other UNIX operating systems.

AS (autonomous system)

A group of networks, often on the same domain, that are operated by the same organization.

IS-IS (Intermediate System to Intermediate System)

A link-state routing protocol that uses a best- path algorithm. IS-IS was originally codified by ISO, which referred to routers as "intermediate systems," thus the protocol's name

checksum

A method of error checking that deter- mines if the contents of an arriving data unit match the contents of the data unit sent by the source.

dynamic routing

A method of routing that automat- ically calculates the best path between two networks and accumulates this information in a routing table.

CSMA/CD (Carrier Sense Multiple Access with Collision Detection)

A network access method specified for use by IEEE 802.3 (Ethernet) networks. In CSMA/CD, each node waits its turn before trans- mitting data to avoid interfering with other nodes' transmissions.

AD (administrative distance)

A number indicating a protocol's reliability, with lower values being given higher priority. This assignment can be changed by a network administrator

neighbor discovery

A process whereby routers learn about all of the devices on their networks. On IPv4 networks, this process is managed by ARP with help from ICMP. On IPv6 networks, NDP (Neighbor Discovery Protocol) automatically detects neighboring devices and automatically adjusts when nodes fail or are removed from the network.

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.

border router

A router that connects an autono- mous system with an outside network—for example, the router that connects a business to its ISP. Also called edge router.

edge router

A router that connects an autonomous system with an outside network—for example, the router that connects a business to its ISP.

exterior router

A router that directs data between autonomous systems, for example, routers used on the Internet's backbone.

core router

A router that directs data between net- works within the same autonomous system.

interior router

A router that directs data between networks within the same autonomous system. Also called core router.

jumbo frame

A setting on Ethernet network devices that allows the creation and transmission of extra-large frames, as high as 9198 bytes

packet sniffer

A software package or hardware- based tool that can capture data on a network.

Layer 3 switch,

A switch capable of interpreting Layer 3 data and works much like a router in that it supports the same routing protocols and makes routing decisions.

Layer 4 switch

A switch capable of interpreting Layer 4 data, which means it can perform advanced filtering, keep statistics, and provide security functions.

static routing

A technique in which a network administrator programs a router to use specific paths between networks.

three-way handshake

A three-step process in which Transport layer protocols establish a connection between nodes. The three steps are: Node A issues a SYN packet to node B, node B responds with SYN-ACK, and node A responds with ACK.

link-state routing protocol

A type of routing protocol that enables routers to share information beyond neighboring routers, after which each router can independently map the network and determine the best path between itself and a message's destination node.

EGP (exterior gateway protocol)

A type of routing protocol used by edge routers and exterior routers to distribute data outside of autonomous systems. BGP is the only modern example of an exterior gateway protocol.

IGP (interior gateway protocol)

A type of routing protocol, such as OSPF and IS-IS, used by core routers and edge routers within autonomous systems.

routing cost

A value assigned to a particular route as judged by the network administrator; the more desirable the path, the lower its cost.

OSPF (Open Shortest Path First)

An IGP and link-state routing protocol that makes up for some of the limitations of RIP and can coexist with RIP on a network.

EIGRP (Enhanced Interior Gateway Routing Protocol)

An advanced distance-vector protocol devel- oped by Cisco that combines some of the features of a link-state protocol and so is sometimes referred to as a hybrid protocol.

RIPv2 (Routing Information Protocol version 2)

An updated version of the original RIP routing protocol that generates less broadcast traffic and functions more securely than its predecessor. However, RIPv2's packet forwarding is still limited to a maximum 15 hops.

BGP (Border Gateway Protocol)

Dubbed the "protocol of the Internet," this path-vector routing protocol is the only current EGP and is capable of considering many factors in its routing metrics.

protocol analyzer

Hardware or software that captures packets to decode and analyze their contents.

routing metric

Properties of a route used by routing protocols to determine the best path to a destination when various paths are available. Routing metrics may be calculated using any of several variables, including hop count, bandwidth, delay, MTU, cost, and reliability.

spoofing

The act of impersonating fields of data in a transmission, such as when a source IP address is impersonated in a DRDoS attack.

Ethernet II

The current Ethernet standard. Ethernet II is distinguished from other Ethernet frame types in that it contains a 2-byte type field to identify the upper-layer protocol contained in the frame.

latency

The delay between the transmission of a signal and its receipt.

MTU (maximum transmission unit)

The largest IP packet size in bytes allowable by routers in a path without fragmentation and excluding the frame size.

routing protocol

The means by which routers communicate with each other about network status. Routing protocols determine the best path for data to take between networks.

best path

The most efficient route from one node on a network to another, as calculated by a router.

hop limit

The number of times that an IPv6 packet can be forwarded by routers on the network; similar to the TTL field in IPv4 pack

RIP (Routing Information Protocol)

The oldest routing protocol that is still widely used, RIP is a distance-vector protocol that uses hop count as its routing metric and allows up to only 15 hops. Compared with other, more modern, routing protocols, RIP is slower and less secure.

collision domain

The portion of an Ethernet network in which collisions could occur if two nodes transmit data at the same time. Today, switches and routers separate collision domains.

gateway of last resort

The router on a network that accepts all unroutable messages from other routers.

distance-vector routing protocol,

The simplest type of routing protocols; used to determine the best route for data based on the distance to a destination.

convergence time

The time it takes for a router to recognize a best path in the event of a change or network outage.

hop

The trip a unit of data takes from one connec- tivity device to another. Typically, hop is used in the context of router-to-router communications.

internetwork

To traverse more than one LAN seg- ment and more than one type of network through a router

hybrid routing protocol

l A routing protocol that exhibits characteristics of both distance-vector and link-state routing protocols

collision

n In Ethernet networks, the interference of one node's data transmission with the data transmis- sion of another node sharing the same segment.