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Chapter 8
Exam 3
65
Other
Undergraduate 4
12/02/2009

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Term
Interfaces
Definition
in routers, ports are called interfaces
Term
Routing
Definition
the forwarding of a packet; the process of exchanging information for building routing tables
Term
Network Part
Definition
the first part of the IP address… identifies the host’s network on the Internet
Term
Internet Networks
Definition
owned by single organizations, such as corporations, universities, and ISPs
Term
Network
Definition
organizational concept: a group of hosts, switched networks, and routers owned by a single organization
Term
Subnet Part
Definition
the second/middle part of the IP address… specifies a particular subnet within the network
Term
Host Part
Definition
the last part of the IP address… identifies a particular host on the subnet
Term
Border Router
Definition
a border router’s main job is to connect different networks
Term
Internal Router
Definition
connects different subnets within a firm
Term
Network Masks
Definition
give the original bits in the network part, followed by zeros
Term
Subnet Masks
Definition
give the original bits in the network and subnet parts, followed by zeros
Term
Route
Definition
forward
Term
Routing Table
Definition
in the routing table, each row represents a route for all IP addresses within a range of IP addresses… typically a network or subnet
Term
Default Row
Definition
the row of a routing table that will be selected automatically if no other row matches; its value is 0.0.0.0
Term
Best-Match Row
Definition
the row that provides the best forwarding option for a particular incoming packet
Term
Longest Match
Definition
the matching row that matches a packet’s destination IP address to the greatest number of bits; chosen by a router when there are multiple matches
Term
Metric Column
Definition
displays numbers describing the desirability of a route represented by a certain row in a routing table
Term
Next-Hop Router (NHR)
Definition
a router to which another router forwards a packet in order to get the packet a step closer to reaching its destination
Term
Decision Caching
Definition
the remembering of a decision made for a destination IP address and using it for successive packets with the same destination
Term
Address Resolution Protocol (ARP)
Definition
protocol for address resolution used in Ethernet networks. If a host or router knows a target host’s or router’s IP address, ARP finds the target host data link layer address
Term
ARP Cache
Definition
section of memory that stores known pairs of IP addresses and switched network standards
Term
IP version 4 (IPv4)
Definition
standard that governs most routers on the Internet and on private internets
Term
Time to Live (TTL)
Definition
the field added to a packet and given a value by a source host, usually between 64 and 128. Each router along the way decrements the TTL field by one. A router decrementing the TTL to zero will discard the packet; this prevents misaddressed packets from circulating endlessly in search of their nonexistent destinations
Term
Protocol Field
Definition
in IP, a field that designates the protocol of the message in the IP packet’s data field
Term
Identification Field
Definition
in IPv4, header field used to reassemble fragmented packets. Each transmitted packet is given a unique identification field value. If the packet is fragmented en route, all fragments are given the initial packet’s identification field value
Term
Fragment Offset Field
Definition
In IPv4, a flag field that tells a fragment’s position in a stream of fragments from an initial packet.
Term
Options
Definition
options are suspicious because they are uncommon and usually used by attackers
Term
Diff-Serv Field
Definition
the field in an IP packet that can be used to label IP packets for priority and other service parameters
Term
IP version 6 (IPv6)
Definition
a new version of the Internet Protocol whose most important change is an increase in the size of IP address fields from 32 bits to 128 bits. This means that instead of supporting 232 unique addresses, it can now support 2128 addresses
Term
Transmission Control Protocol (TCP)
Definition
TCP takes care of the more complex internetwork transmission control tasks. TCP messages are called TCP segments
Term
Sequence Number Field
Definition
In TCP, a header field that tells a TCP segment’s order among the multiple TCP segments sent by one side
Term
Acknowledgment Number Field
Definition
In TCP, a header field that tells what TCP segment is being acknowledged in a segment
Term
Flag Fields
Definition
a one-bit field
Term
Set
Definition
the condition of a flag field if it has a value of 1
Term
Three-way Handshake
Definition
a three-message exchange that opens a connection in TCP. (SYN, SYN/ACK, ACK)
Term
Four-way Close
Definition
a normal TCP connection close; requires four messages (FIN, ACK, FIN, ACK)
Term
FIN
Definition
One-bit field in a TCP header; indicates that the sender wishes to close a TCP connection
Term
Abrupt Reset
Definition
a second way to close TCP connections (it is like hanging up the phone)
Term
RST bit
Definition
in a TCP segment, if the RST bit is set, this tells the other side to end the connection immediately
Term
Port Number
Definition
the field in TCP and UDP that tells the transport process what application process sent the data in the data field or should receive the data in the data field
Term
Well-known Port Numbers
Definition
standard port number of a major application that is usually (but not always) used. For example, the well known TCP port number for HTTP is 80.
Term
Ephemeral Port Numbers
Definition
the temporary number a client selects whenever it connects to an application program on a server. According to IETF rules, ephemeral port numbers should be between 49153 and 65535
Term
Socket
Definition
the combination of an IP address and a port number, designating a specific connection to a specific application on a specific host. It is written as an IP address, a colon, and a port number, for instance 128.171.17.13:80
Term
User Datagram Protocol (UDP)
Definition
a simple (connection-less and unreliable) protocol used by VoIP because there is no time to wait for retransmissions. SNMP uses UDP to reduce network traffic
Term
Length
Definition
the field in a UDP datagram that enables the receiving transport process to process the datagram properly
Term
UDP Checksum
Definition
the field in a UDP datagram that allows the receiver to check for errors. If an error is found, the UDP datagram is discarded
Term
Dynamic Routing Protocols
Definition
a protocol used by routers to exchange routing table information
Term
Autonomous System
Definition
Internet network owned by an organization
Term
Interior Dynamic Routing Protocols
Definition
dynamic routing protocols used for internal networks (internets). There are three popular interior dynamic routing protocols: RIP, OSPF, EIGRP
Term
Routing Information Protocol (RIP)
Definition
a simple but limited interior routing protocol whose metric is merely the number of router hops needed to get to the destination host. Its simplicity makes it attractive for smaller internets but has poor security
Term
Open Shortest Path First (OSPF)
Definition
complex but highly scalable interior routing protocol. OSPF is very efficient, having a complex metric based on a mixture of cost, throughput, and traffic delays. OSPF also offers a strong security. It costs much more to manage than RIP but is the only routing protocol that makes sense for larger internets
Term
Enhanced Interior Gateway Routing Protocol (EIGRP)
Definition
interior routing protocol used by Cisco routers. It can route SNA and IPX/SPX traffic as well as IP traffic but it is a proprietary protocol which forces users of EIGRP to buy only Cisco routers
Term
Gateway
Definition
another term for router
Term
Border Gateway Protocol (BGP)
Definition
almost universally used routing protocol designed specifically for the exchange of routing information between autonomous systems
Term
Internet Control Message Protocol (ICMP)
Definition
the protocol created by the IETF to oversee supervisory messages at the internet layer. ICMP messages are encapsulated in the data field of IP messages
Term
ICMP Error Message
Definition
in ICMP, an error advisement message
Term
Error Advisement
Definition
in ICMP, the process wherein if an error is found, there is no transmission, but the router or host that found the error usually sends an ICMP error message to the source device to inform it that an error has occurred. It is then up to the device to decide what to do (this is not the same as error correction because there is no mechanism for the retransmission of lost or damaged packets)
Term
ICMP Echo
Definition
most famous ICMP error message type. One host or router can send an echo request message to another. If the target device’s internet process is able to do so, it will send back an echo reply message. Echo is a good diagnostic tool because if there are network difficulties, a logical early step in diagnosis is to ping many hosts and routers to see whether they can be reached
Term
Pinging
Definition
sending a message to another host and listening for a response to see if it is active. Another term for an ICMP echo
Term
Static IP Addresses
Definition
an IP address that never changes. Most servers have static IP addresses so that they can be found easily
Term
Dynamic IP
Definition
IP address that is different each time the user goes on the Internet
Term
Dynamic Host Configuration Protocol (DCHP)
Definition
the protocol used by DHCP servers, which provide each user PC with a temporary IP address each time he or she connects to the Internet
Term
Layer 3 Switches
Definition
a router that does processing in hardware and that is much faster and less expensive than traditional software-based routers. Layer 3 switches are usually dominant in the Ethernet core above workgroup switches. Hardware based routers have less functionality than software based routers
Term
Layer 4 Switches
Definition
a switch that examines the port number fields of each arriving packet’s encapsulated TCP segment, allowing it to switch packets based on the application they contain. Layer 4 switches can give priority or even deny forwarding to IP packets from certain applications
Term
Application Switches
Definition
make switching decisions according to the content of application messages. Application switches may determine where the application message goes and what priority the message should be given
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