Chapter 1 - Introduction to TCP/IP Networking

Table 1-5 is a reference model for the OSI model, the protocols and specifications, and the device types.

5. Application, presentation, and session (Layer 5 - 7) layer utilizes Telnet, HTTP, FTP, SMTP, POP3, VoIP, SNMP, and run on hosts or firewalls. 4. Transport (Layer 4) layer utilizes TCP, UDP and runs on hosts and firewalls. 3. Network (Layer 3) layer utilizes IP and runs on routers. 2. Data Link (Layer 2) layer utilizes Ethernet (IEEE 802.3), HDLC and runs on switches, wireless access points (WAP's), and lastly Cable and DSL modems. 1. Physical (Layer 1) layer utilizes RJ-45, Ethernet (IEEE 802.3) and runs on hubs, repeaters and cables.

What are the seven layers of the OSI model?

7. Application 6. Presentation 5. Session 4. Transport 3. Network 2. Data Link 1. Physical

What does each layer of the OSI model entails?

7. Application layer. Provides an interface from the application to the network by supplying a protocol with actions meaningful to the application, for example, "get web page object." 6. Presentation layer. This layer negotiates data formats, such as ASCII text, or image types like JPEG. 5. Session layer. This layer provides methods to group multiple bidirectional messages into a workflow for easier management and easier backout of work that happened if the entire workflow fails. 4. Transport layer. In function, much like TCP/IP's transport layer. This layer focuses on data delivery between the two endpoint hosts (for example, error recovery). 3. Network layer. Like the TCP/IP network (Internet) layer, this layer defines logical addressing, routing (forwarding), and the routing protocols used to learn routes. 2. Data Link layer. Like the TCP/IP data link layer, this layer defines the protocols for delivering data over a particular single type of physical network (for example, the Ethernet data link protocols). 1. Physical layer. This layer defines the physical characteristics of the transmission medium, including connectors, pins, use of pins, electrical currents, encoding, light modulation, and so on.

Note: In networking diagrams, what represents a part of a network whose details are not important to the purpose of the diagram. In this case, Figure 1-2 ignores the details of how to create an enterprise network.

A cloud diagram represents a part of a network not necessary for the example.

What is a router?

A router is a networking device that connects TCP/IP networks together for the purpose of routing (forwarding) IP packets from source to destination. A router does the equivalent of the work done by each post office site: they receive IP packets on various physical interfaces, make decisions based on the IP address included with the packet, and then physically forward the packet out a different network interface.

In the event that information fails to traverse a TCP/IP network, what mechanism is used by TCP error recovery to guarantee delivery of data?

Acknowledgements

The previous example mentioning sequence numbers and error recovery, and shown in Figure 1-7 also demonstrates a function called what?

Adjacent-layer interaction In this example, the higher-layer protocol (Layer 7 - HTTP) wants error recovery, and the higher layer uses the next lower-layer protocol (Layer 4 - TCP) to perform the service of error recovery; the lower layer provides a service to the layer above it.

What are some example protocols associated with the TCP/IP Architecture Layers in Table 1-2? Application Transport Internet Link

Application - HTTP, POP3, SMTP Transport - TCP, UDP Internet - IP Link - Ethernet, Point-to-Point Protocol (PPP), T1

What are the four names for the Physical, Data Link, Network and Transport messages?

Bits, Frames, Packets and Segments

IP addressing such as 1.1.1.1, or 2.2.2.2 is a style called what?

Dotted-decimal notation (DDN)

What single service provided by TCP would come into play if a HTTP GET request is lost in transit?

Error recovery

True or False? If you request a web page from a web server, it will continuously send the same HTTP Header when forwarding more data?

False. Step 3 in Figure 1-6 shows another message from web server Larry to web browser Bob, but this time without an HTTP header. HTTP transfer the data by sending multiple messages, each with a part of the file. Rather than wasting space by sending repeated HTTP headers that list the same information, these additional messages simply omit the header.

What is a basic four step example of how the link-layer works with the network-layer to forward traffic?

Figure 1-11 shows four steps. The first two occur on the web server, and the last two occur on the router (R1). Step 1. The web server encapsulates the IP packet between a header and a trailer, creating an Ethernet frame. Step 2. The web server physically transmits the bits of this Ethernet frame, using electricity flowing over the Ethernet cabling. Step 3. Router R1 physically receives the electrical signal over a cable, and re-creates the same bits by interpreting the meaning of the electrical signals. Step 4. Router R1 de-encapsulates the IP packet from the Ethernet frame by removing and discarding the Ethernet header and trailer. By the end of this process, the link-layer processes on the web server and R1 have worked together to deliver the packet from the webserver to Router R1.

When comparing the postal service to routing, what's the equivalent of home addresses to computers?

Home addresses are comparable to IP addresses. Just like how home addresses need to have unique apartment numbers, road's, zip codes, etc.; devices operating under the TCP/IP model, primarily defined by the Internet Protocol (IP), each computer should have a different IP address. IP defines the process of routing at Layer 3, so that devices called routers can work like the post office, forwarding packets of data so that they are delivered to the correct destinations.

Note: The term ___ ___ refers to any device, regardless of size or power, that has an IP address and connects to any TCP/IP network.

IP host

The process of forwarding IP packets is called what?

IP routing (or simply routing)

What is a basic example of how TCP acknowledges work?

In Figure 1-7, it outlines the basic idea behind how TCP notices lost data and asks the sender to try again. In this example, a web browser requests a web page from a web server. The web server then sends a TCP header with a sequence number, HTTP OK reply, and Data. This data succeeds, but when the subsequent data regarding the web page is lost, the end-user's web browser notices the TCP message (segment) with a particular sequence number is missing. Let's say SEQ = 1, and SEQ = 3 succeeds, but SEQ = 2 is dropped in transit. The web browser will send a TCP segment back to the web server, asking the web server to send message 2 (SEQ = 2) again.

Today, what model can be used as a standard of comparison to other networking models such as TCP/IP?

Open Systems Interconnection (OSI) model

What's a basic example on how HTTP functions between two end-points?

Person A will open a web browser, and request a web page from Person B. That request is sent to the web server hosted by Person B. Person B's web server will then process the request down the TCP/IP stack, and provide the home.htm file for the home page.

The original TCP/IP model can be found in which RFC?

RFC 1122

The TCP/IP model both defines and references a large collection of protocols that allow computers to communicate. To define a protocol, TCP/IP uses documents called what?

Requests For Comments (RFC)

What is the HTTP return code for an OK reply?

Return code (200).

Figure 1-7 also shows an example of a similar function to adjacent-layer interaction called what?

Same-layer interaction When a particular layer on one computer wants to communicate with the same layer on another computer, the two computers use headers to hold the information that they want to communicate. The web server's TCP process created the TCP headers with the sequence numbers; the end-user's TCP process received and reacted to the TCP segments.

What is the term for smaller networks often used for home use, or small mom and pop shops?

Small Office / Home Office (SOHO)

What are the five steps when encapsulating data on a TCP/IP host?

Step 1. Create and encapsulate the application data with any required application layer headers. For example, the HTTP OK message can be returned in an HTTP header, followed by part of the contents of a web page. Step 2. Encapsulate the data supplied by the application layer inside a transport layer header. For end-user applications, a TCP or UDP header is typically used. Step 3. Encapsulate the data supplied by the transport layer inside a network layer (IP) header. IP defines the IP addresses that uniquely identify each computer. Step 4. Encapsulate the data supplied by the network layer inside a data link layer header and trailer. This layer uses both a header and a trailer. Step 5. Transmit the bits. The physical layer encodes a signal onto the medium to transmit the frame.

What are the two most popular TCP/IP transport layer protocols?

TCP and UDP

TCP/IP actually has two alternative models, as shown in Figure 1-4. What are they called?

TCP/IP Original was Link, Internet, Transport and Application. TCP/IP Updated is Physical, Data Link, Network, Transport, and Application.

What does TCP/IP stand for, and what does it mean?

TCP/IP stands for Transmission Control Protocol/Internet Protocol and it's a common name for the suite of protocols developed by the U.S Department of Defense in the 1970's to support the construction of worldwide internetworks. TCP and IP are the two best-known protocols in the suite.

What does a return code of 200 (HTTP OK reply) do?

The HTTP 200 OK success status response code indicates that the request has succeeded. A 200 response is cacheable by default. The meaning of a success depends on the HTTP request method. GET: The resource has been fetched and is transmitted in the message body.

If the TCP/IP model refers to Layer 1 - 4 messages as Bits, Frames, Packets and Segments, what does the OSI model refer to these messages as?

The OSI models refers to these messages as protocol data units (PDU's). A PDU represents the bits that include the headers and trailers for that layer, as well as the encapsulated data. For example, an IP packet, as shown in Figure 1-14, using OSI terminology, is a PDU, more specifically a Layer 3 PDU (abbreviated L3PDU) because IP is a Layer 3 protocol. OSI simple refers to the Layer x PDU (LxPDU), with x referring to the number of the layer being discussed, as show in Figure 1-16.

Routing data across a network is most notably compared to what example?

The postal service This is because just like data being routed across a LAN or WAN, envelopes being sent from source to destination is similar. If you have a package to send to a friend in town, you just need to drop it off at the post office and they'll forward it onto the correct truck. However, if you have a package for a friend across the country, it's going to be sent between one post office to another post office, then another, and so on, until the package gets delivered across the country.

TCP/IP defines two versions of IP. What are they, and which one most well known and established whereas the latter being up and coming?

The two different versions of IP is IP version 4 (IPv4), and IP version 6 (IPv6). IPv4 is still renowned across the world, with IPv6 steadily growing in popularity.

What's a more technical example on how HTTP functions between two end-points?

The web browser will construct a HTTP Header with a GET request for home.htm. The web server will send back a HTTP Header with a OK reply, including the Data of home.htm. If needed, the web server will send more data with information regarding home.htm.

The process of a web server adding a TCP header to the contents of a web page, followed by adding an IP header and then adding a data link header and trailer, is an example of what? a. Data encapsulation b. Same-layer interaction c. OSI model d. All of these answers are correct.

a. Data encapsulation

Which of the following protocols are examples of TCP/IP data link layer protocols? (Choose two answers.) a. Ethernet b. HTTP c. IP d. UDP e. SMTP f. TCP g. PPP

a. Ethernet g. PPP

Note: Protocols defines both ___ and ___ for the same general reason, but ___ exists at the beginning of the message and ___ exists at the end.

a. Headers b. Trailers

Which OSI layer defines the standards for cabling and connectors? a. Layer 1 b. Layer 2 c. Layer 3 d. Layer 4 e. Layer 5, 6, or 7

a. Layer 1

What are two different perspectives on networks from a home-user?

a. PC uses Ethernet cable (RJ-45) to connect to the modem, and then connects to "The Internet" via CATV (Coaxial)(RJ-6) cable. b. PC or Tablet uses Wireless (802.11 a/b/g/n) to connect to the modem, and then connects to "The Internet" via Digital Subscriber Line (DSL).

Note: The full version of most web addresses - also called ___ or ___ - begins with the letters http, which means that HTTP is used to transfer the web pages.

a. Uniform Resource Locators (URL) b. Universal Resource Identifies (URI)

Note: The original TCP/IP model's link layer has also been referred to as what two things?

a. network access layer b. network interface layer

A ___ , sometimes also called either a ___ or ____ , refers to a comprehensive set of documents. Individually, each document describes one small function required for a network; collectively, these documents define everything that should happen for a computer network to work. For example, a document could define the voltage and current levels used on a particular cable when transmitting data.

a. networking model b. networking architecture c. networking blueprint

The process of HTTP asking TCP to send some data and making sure that it is received correctly is an example of what? a. Same-layer interaction b. Adjacent-layer interaction c. OSI model d. All of these answers are correct.

b. Adjacent-layer interaction

The process of TCP on one computer marking a TCP segment as segment 1, and the receiving computer then acknowledging the receipt of TCP segment 1 is an example of what? a. Data encapsulation b. Same-layer interaction c. Adjacent-layer interaction d. OSI model e. All of these answers are correct.

b. Same-layer interaction

Which OSI layer defines the functions of logical network-wide addressing and routing? a. Layer 1 b. Layer 2 c. Layer 3 d. Layer 4 e. Layer 5, 6, or 7

c. Layer 3

Which of the following terms is used specifically to identify the entity created when encapsulating data inside data link layer headers and trailers? a. Data b. Chunk c. Segment d. Frame e. Packet

d. Frame

Which of the following protocols are examples of TCP/IP transport layer protocols? (Choose two answers.) a. Ethernet b. HTTP c. IP d. UDP e. SMTP f. TCP

d. UDP f. TCP

The term ___ refers to the process of putting headers (and sometimes trailers) around some data?

encapsulation