Cis 370 Exam 1

Front 1

Protocols

Back 1

End systems and packet switches run protocols that control and maintain the sending of information. Protocols are like the rules that are followed when dealing with any networks that transfer information between each other. A protocol defines the format and the order of messages exchanged between two or more communicating entities, as well as the actions taken on the transmission and/or receipt of a message or other event.

Front 2

Encapsulation

Back 2

Encapsulation is a method of designing modular communication protocols in which logically separate functions in the network are abstracted from their underlying structures by inclusion or information hiding within higher level objects.

Front 3

Networking Media

Back 3

Physical media is what the bit uses to transfer or transmit in the physical medium. Physical media is stuff like fiber optical cables and radio spectrums and etc. but the physical media is grouped into two different categories, guided and unguided. Guided media transfers along a solid medium such as fiber optic, coaxial, or twisted pair. Unguided use waves that propagate in space or the atmosphere.

Front 4

Packet Switching

Back 4

Packet Switching is the process in which packets are transferred over packet switches like routers and link layers. It uses networking media like routers and wires to transfer the packets over the network. There is sometimes problems like congestions or queues that it has to deal with and wait over, but the bottom line for packet switching is that it gets to its destination and if it doesn’t it can retransmit or ask for the pieces that it didn’t receive from the other sender. Here is more from the notes on it, Packets are sent to packet switches, like routers and link layer switches. Then packets are transmitted over the communication link at a certain rate. So the rate of transfer is L/R. Most packets use the store and forward transmission input. This means that the packet switch must receive the entire packet before it can begin to transmit the first bit of the packet. Each packet switch has multiple links attached to it. For each link, the packet switch has an output buffer and that is also called and o

Front 5

Packet Sniffing

Back 5

Packet sniffing is the act of capturing packets of data flowing across a computer network. The software or device used to do this is called a packet sniffer. Packet sniffing is to computer networks what wiretapping is to a telephone network.

Front 6

TCP

Back 6

TCP is a connection based protocol that establishes a connection with another end by doing a three way handshake. First it sends a SYN packet to the host it wants to connect to, then the other host will respond to the SYN with an ACK packet and then to end the handshake a SYN ACK is sent back to establish the connection.

Front 7

IP

Back 7

IP specifies the formats the packets that are sent between machines. An Internet Protocol address (IP address) is a numerical label assigned to each device (e.g., computer, printer) participating in a computer network that uses the Internet Protocol for communication. An IP address serves two principal functions: host or network interface identification and location addressing. Its role has been characterized as follows: A name indicates what we seek. An address indicates where it is. A route indicates how to get there.

Front 8

Throughput

Back 8

In communication networks, such as Ethernet or packet radio, throughput or network throughput is the average rate of successful message delivery over a communication channel. This data may be delivered over a physical or logical link, or pass through a certain network node. The throughput is usually measured in bits per second (bit/s or bps), and sometimes in data packets per second or data packets per time slot.

Front 9

Application Programming Interface (API)

Back 9

End systems that are attached to the internet provide an API or Application Programming Interface that specifies how a program running on one end system asks the internet how it delivers data to a specific destination program.

Front 10

Socket

Back 10

The messages sent by these processes are sent into and received from a network through a software interface called a socket. A socket is the interface between the application layer and the transportation layer within a host.

Front 11

Non-persistent connections

Back 11

Non-persistent connections can obtain 1 connection to obtain a picture from a website, and then obtain a different connection to get another picture. The connections aren’t the same.

Front 12

Web Caching

Back 12

Web Cache also called a Proxy Server is a network entity that satisfies HTTP requests on behalf of an origin web server. The cache has its own disk storage and keeps copies of recently requested objects. The cache is kind of like a middle man between connections. Lets say I was trying to connect to a site to obtain a picture, with HTTP, I will connect to the web cache, and if the cache has that particular picture I want stored locally, then it will just respond with the picture in it’s response message, however, if the cache doesn’t have the picture, it makes the connection to the website, and keeps the process going. Typically the cache is purchased and installed by an ISP. Through the use of Content Distribution Networks, web cache’s are increasingly playing an important role on the internet. A CDN installs many geographically distributed caches. To prevent anything from staying in the cache for to long, HTTP uses a conditional get statement.

Front 13

DNS Caching

Back 13

DNS Caching is a very important feature offered by DNS. In a simple form of explanation, in a query chain, when a DNS server receives a DNS reply that contains a lot of mapping information, it can cache in its local memory. DNS servers that implement the DNS distributed database, store Resource Records (RR) that provide Hostname-to-IP addressing mapping. NSLOOKUP allows you to send a DNS query directly to the DNS server you are working with on your system by command prompt.

Front 14

DNS Vulnerabilities

Back 14

DNS cache poisoning (sometimes referred to as cache pollution) is an attack technique that allows an attacker to introduce forged DNS information into the cache of a caching name server. DNS cache poisoning is not a new concept; in fact, there are published articles that describe a number of inherent deficiencies in the DNS protocol and defects in common DNS implementations that facilitate DNS cache poisoning. The following are examples of these deficiencies and defects.

Front 15

Logical Communication

Back 15

A transport layer provides for logical communication between application processes running on different hosts. By logical communication we mean that from an application’s perspective, it is as if the hosts running the processes were directly connected; in reality the hosts may be on opposite sides of the world connected by numerous routers and link types. Application processes use logical communication provided by the transport layer to send messages to each other free from the worry of the details of the physical infrastructure to carry out these messages.

Front 16

Port Scanning

Back 16

The act of systematically scanning a computer's ports. Since a port is a place where information goes into and out of a computer, port scanning identifies open doors to a computer. Port scanning has legitimate uses in managing networks, but port scanning also can be malicious in nature if someone is looking for a weakened access point to break into your computer.

Front 17

End-end Principle

Back 17

The principle that states how each layer in end to end communication specifically does its own function to help reduce redundancy in the process of end to end communication.

Front 18

Maximum Segment Size

Back 18

A TCP connection provides a full-duplex service which means data can flow between two hosts at the same time. TCP is also point-to-point which is between a single sender and a single receiver.
The maximum segment size or MSS is the maximum amount of data that can be grabbed and placed in a segment.

Front 19

Acknowledgement Number (ACK) And Sequence Number

Back 19

Bottom line, Sequence and Acknowledgement numbers are 32 bit numbers used by TCP to track data that is sent, received, and outstanding. TCP keeps track of data by assigning a sequence number to each byte sent, and then it uses the corresponding acknowledgement numbers to determine if any data was lost in transit. At the beginning of a TCP connection, each side will start by using an Initial Sequence Number (ISN) derived from a unique clock value from 0 to 4,294,967,295.

Front 20

Duplicate ACK

Back 20

Is when the receiver sends out a duplicate ACK telling the sender that it hasn’t received all of the packets yet. The sender however doesn’t retransmit the packet until it has received three ACK’s. It does this because the packet still may arrive at the destination out of order and if it was to send another packet to the receiver and the receiver was to receive the rest of the packet, it would just duplicate the packet, causing more congestion in the network.

Front 21

SYN Flood Attack

Back 21

SYN Flood Attack is when an attacker sends a large number of TCP SYN segments to exhaust the connection resources and not completing the third part of the handshake.

Front 22

Demultiplexing

Back 22

Is delivering data in the transport layer segment, to the correct socket. Sockets are doors through which data passes through from the network to the process and through which data passes from the process to the network.

Front 23

Multiplexing

Back 23

Gathering data chunks at the source host from different sockets, encapsulating each data chunk with header information to create segments, and passing the segments to the network layer.