Chapter 3: How Data is Transported Over Networks
A TCP/IP troubleshooting utility available in Linux, UNIX, and OS X 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.
traceroute
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.
tracert
A process whereby routers learn about all of the devices on their networks.
neighbor discovery Additional Info: 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.
An error that is reported when a logical (not physical) connection between a node and a network is malfunctioning. They can be prompted by any number of problems, including interface misconfiguration.
interface errors
A router that directs data between networks within the same autonomous system.
interior routers
To traverse more than one LAN segment and more than one type of network through a router.
internetwork
A setting on Ethernet network devices that allows the creation and transmission of extra-large frames, as high as 9198 bytes, depending on the type of Ethernet architecture used.
jumbo frame
The delay between the transmission of a signal and its receipt.
latency
A TCP/IP troubleshooting utility that displays statistics and details about TCP/IP components and connections on a host. It also displays ports, which can signal whether services are using the correct ports.
netstat
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.
link-state routing protocols
The traffic or processing burden sustained by a router in the path.
load
A TCP/IP troubleshooting utility that provides information about NetBIOS names and their IP addresses.
nbtstat (NetBios over TCP/IP Statistics) Additional Info: If you know the NetBIOS name of a workstation, you can use nbtstat to determine its IP address.
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.
pathping
How do you stop a command while it's still running?
press CTRL + C
A repeated trial message transmitted by the tracert and traceroute utilities to trigger routers along a route to return specific information about the route.
probes
ARP is a layer ____ protocol
2 (Data Link Layer) Additional Info: It uses IP in layer 3, and operates only within its local network bound by routers
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.
Dynamic ARP table entries
A type of routing protocol used by border routers and exterior routers to distribute data outside of autonomous systems.
EGP (exterior gateway protocols) Additional Info: BGP is the only modern example of an exterior gateway protocol.
A router that directs data between autonomous systems, for example, routers used on the Internet's backbone.
Exterior routers
True or False? IP ensures data packets are delivered to the right addresses?
False. IP is an unreliable, connectionless protocol. IP depends on TCP to ensure that data packets are delivered to the right addresses.
A Network layer protocol used on IPv4 networks to manage multicast transmissions.
IGMP (Internet Group Management/Multicast Protocol) Additional Info: Routers use IGMP to determine which nodes belong to a multicast group, and nodes use IGMP to join or leave a multicast group.
A type of routing protocol, such as OSPF and IS-IS, used by interior routers and border routers within autonomous systems.
IGP (interior gateway protocols)
A link-state routing protocol that uses a best-path algorithm similar to OSPF's. This protocol was originally codified by ISO, which referred to routers as "intermediate systems," thus the protocol's name. Unlike OSPF, this protocol is designed for use on interior routers only.
IS-IS (Intermediate System to Intermediate System)
The sequence number in the first SYN message in a three-way handshake. This number appears to be random, but in reality, it is calculated by a specific, clock-based algorithm, which varies by operating system.
ISN (Initial Sequence Number)
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 3 switch
A switch capable of interpreting Layer 4 data, which means it can perform advanced filtering, keep statistics, and provide security functions.
Layer 4 switch
An online database that correlates manufacturers with their respective OUIs.
MAC address lookup tables
A supervisory computer or server in an ICS or SCADA system that controls the physical system. Also called the control server or the SCADA server.
MTU (maximum transmission unit)
A problem that occurs when a router receives a message that is too large for the next segment's MTU. The router returns an ICMP error message to the sender, but the error message is not returned correctly. From the sender's perspective, messages are lost for no apparent reason.
MTU black hole
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.
OSPF (Open Shortest Path First)
The oldest routing protocol that is still widely used, this routing protocol 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, this protocol is slower and less secure.
RIP (Routing Information Protocol)
An updated version of the original RIP routing protocol that generates less broadcast traffic and functions more securely than its predecessor. This version is still limited to 15 hops.
RIPv2 (Routing Information Protocol version 2)
A number indicating a protocol's reliability, with lower values being given higher priority. This assignment can be changed by a network administrator when one protocol should take precedence over a previously higher-rated protocol on a network.
AD (Administrative Distance)
A database of records that maps MAC addresses to IP addresses.
ARP table/cache Additional Info: 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.
A globally unique number that identifies an autonomous system. These work similarly to IP addresses that identify individual nodes on a network.
ASN (autonomous system number) Additional Info: Each ASN now consists of 32 bits instead of 16 bits, and they are assigned by IANA.
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.
BGP (Border Gateway Protocol)
A router that connects an autonomous system with an outside network—for example, the router that connects a business to its ISP.
Border/gateway routers
Logically grouped network nodes that can communicate directly via broadcast transmissions.
Broadcast domain Additional Info: By default, switches and repeating devices, such as hubs, extend broadcast domains. Routers and other Layer 3 devices separate broadcast domains.
What are the three parts of a TCP three-way handshake?
Checksums sequencing flow control
A record in an ARP table that someone has manually entered using the ARP utility.
Static ARP table entries Addtional Info: Static ARP table entries remain the same until someone manually modifies them with the ARP utility.
True or False? Command parameters can be combined into a single command.
True For example, entering the command netstat -an will display the IP addresses and port numbers of active TCP connections and listening TCP and UDP ports.
The time it takes for a router to recognize a best path in the event of a change or network outage.
convergence time
A routing protocol that exhibits characteristics of both distance-vector and link-state routing protocols.
hybrid routing protocol
A group of networks, often on the same domain, that are operated by the same organization.
autonomous system (AS)
The most efficient route from one node on a network to another, as calculated by a router.
best path
A method of error checking that determines if the contents of an arriving data unit match the contents of the data unit sent by the source.
checksum
One of several types of specialized devices that allows two or more networks or multiple parts of one network to connect and exchange data.
connectivity devices
A backup route, usually to another router, used when a router cannot determine a path to a message's destination.
default route
The simplest type of routing protocols; used to determine the best route for data based on the distance to a destination.
distance-vector routing protocols Additional Info: Some distance-vector routing protocols only factor in the number of hops to the destination, while others take into account latency and other network traffic characteristics.
A method of routing that automatically calculates the best path between two networks and accumulates this information in a routing table.
dynamic routing Additional Info: If congestion or failures affect the network, a router using dynamic routing can detect the problems and reroute data through a different path. Modern networks primarily use dynamic routing.
A sequence of packets issued from one source to one or many destinations.
flow Additional Info: Routers interpret flow information to ensure that packets belonging to the same transmission arrive together. Flow information may also help with traffic prioritization.
A method of gauging the appropriate rate of data transmission based on how fast the recipient can accept data.
flow control
The router on a network that accepts all unroutable messages from other routers.
gateway of last resort
A command-line tool that shows a host's routing table.
route command Additional Info: On a Linux or UNIX system, such as OS X (the operating system on Apple computers), you can view the routing table by entering route at the command prompt. On a Windows-based system, use the command route print instead. On a Cisco-brand router or another brand that uses Cisco command conventions, use the command show ip route.
A complex, manual process in which route information from one routing protocol is adapted to another routing protocol's specifications.
route redistribution
A value assigned to a particular route as judged by the network administrator; the more desirable the path, the lower its cost.
routing cost
A problem that happens when a message gets stuck in a loop between a limited number of routers without ever reaching its destination.
routing loop
Properties of a route used by routing protocols to determine the best path to a destination when various paths are available.
routing metrics Additional Info: Routing metrics may be calculated using any of several variables, including hop count, bandwidth, delay, MTU, cost, and reliability.
The means by which routers communicate with each other about network status.
routing protocols Additional Info: Routing protocols determine the best path for data to take between networks.
A database stored in a router's memory that maintains information about the location of hosts and best paths for forwarding packets to them.
routing table
A chronological number that TCP attaches to each segment so the destination host can, if necessary, reorder segments as they arrive.
sequence number
A technique in which a network administrator programs a router to use specific paths between networks.
static routing Additional Info: Because it does not account for occasional network congestion, failed connections, or device moves, and requires manual configuration, static routing is not optimal.
A three-step process in which Transport layer protocols establish a connection between nodes.
three-way handshake Additional Info: 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.