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| in routers, ports are called interfaces |
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| the forwarding of a packet; the process of exchanging information for building routing tables |
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| the first part of the IP address… identifies the host’s network on the Internet |
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| owned by single organizations, such as corporations, universities, and ISPs |
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| organizational concept: a group of hosts, switched networks, and routers owned by a single organization |
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| the second/middle part of the IP address… specifies a particular subnet within the network |
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| the last part of the IP address… identifies a particular host on the subnet |
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| a border router’s main job is to connect different networks |
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| connects different subnets within a firm |
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| give the original bits in the network part, followed by zeros |
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| give the original bits in the network and subnet parts, followed by zeros |
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| in the routing table, each row represents a route for all IP addresses within a range of IP addresses… typically a network or subnet |
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| the row of a routing table that will be selected automatically if no other row matches; its value is 0.0.0.0 |
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| the row that provides the best forwarding option for a particular incoming packet |
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| 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 |
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| displays numbers describing the desirability of a route represented by a certain row in a routing table |
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| a router to which another router forwards a packet in order to get the packet a step closer to reaching its destination |
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| the remembering of a decision made for a destination IP address and using it for successive packets with the same destination |
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| Address Resolution Protocol (ARP) |
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| 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 |
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| section of memory that stores known pairs of IP addresses and switched network standards |
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| standard that governs most routers on the Internet and on private internets |
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| 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 |
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| in IP, a field that designates the protocol of the message in the IP packet’s data field |
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| 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 |
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| In IPv4, a flag field that tells a fragment’s position in a stream of fragments from an initial packet. |
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| options are suspicious because they are uncommon and usually used by attackers |
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| the field in an IP packet that can be used to label IP packets for priority and other service parameters |
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| 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 |
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| Transmission Control Protocol (TCP) |
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Definition
| TCP takes care of the more complex internetwork transmission control tasks. TCP messages are called TCP segments |
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| In TCP, a header field that tells a TCP segment’s order among the multiple TCP segments sent by one side |
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| Acknowledgment Number Field |
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| In TCP, a header field that tells what TCP segment is being acknowledged in a segment |
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| the condition of a flag field if it has a value of 1 |
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| a three-message exchange that opens a connection in TCP. (SYN, SYN/ACK, ACK) |
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| a normal TCP connection close; requires four messages (FIN, ACK, FIN, ACK) |
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| One-bit field in a TCP header; indicates that the sender wishes to close a TCP connection |
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| a second way to close TCP connections (it is like hanging up the phone) |
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| in a TCP segment, if the RST bit is set, this tells the other side to end the connection immediately |
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| 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 |
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| 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. |
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| 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 |
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| 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 |
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| User Datagram Protocol (UDP) |
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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 |
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Definition
| the field in a UDP datagram that enables the receiving transport process to process the datagram properly |
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| the field in a UDP datagram that allows the receiver to check for errors. If an error is found, the UDP datagram is discarded |
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| Dynamic Routing Protocols |
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Definition
| a protocol used by routers to exchange routing table information |
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Definition
| Internet network owned by an organization |
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| Interior Dynamic Routing Protocols |
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Definition
| dynamic routing protocols used for internal networks (internets). There are three popular interior dynamic routing protocols: RIP, OSPF, EIGRP |
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| Routing Information Protocol (RIP) |
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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 |
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| Open Shortest Path First (OSPF) |
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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 |
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| Enhanced Interior Gateway Routing Protocol (EIGRP) |
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| 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 |
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| Border Gateway Protocol (BGP) |
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| almost universally used routing protocol designed specifically for the exchange of routing information between autonomous systems |
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| Internet Control Message Protocol (ICMP) |
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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 |
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Definition
| in ICMP, an error advisement message |
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Term
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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) |
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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 |
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Definition
| sending a message to another host and listening for a response to see if it is active. Another term for an ICMP echo |
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| an IP address that never changes. Most servers have static IP addresses so that they can be found easily |
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Definition
| IP address that is different each time the user goes on the Internet |
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| Dynamic Host Configuration Protocol (DCHP) |
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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 |
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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 |
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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 |
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Term
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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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