Lesson 1: Explaining the OSI and TCP/IP Models CompTIA Network+ (N10-007)

Identify the layer that does not add a header to the data payload. A. Physical B. Network C. Transport D. Application

A At each level, except the Physical layer, the sending nodes adds a header to the data payload which forms a chunk of data called a Protocol Data Unit (PDU). This process is known as encapsulation. At the Network layer, the Transmission Control Protocol (TCP) segment is wrapped in an Internet Protocol (IP) header. The IP packet is put into an Ethernet frame at the Data Link layer. At the Transport layer, a TCP header is added to the application. Data is generated by an application, such as Hypertext Transfer Protocol (HTTP), which will include an application header.

Summarize the purpose of the Internet Engineering Task Force (IETF). A. The IETF focuses on solutions to Internet problems and the adoption of new standards. B. The IETF allocates addresses to regional registries who then allocate them to local registries. C. The IETF encourages the development and availability of the Internet, and provides organizational resources to the IAB. D. The IETF manages allocation of IP addresses and maintenance of the top-level domain space.

A The Internet Engineering Task Force (IETF) focuses on solutions to Internet problems and the adoption of new standards. The IETF is governed by the Internet Architecture Board (IAB). The Internet Assigned Numbers Authority (IANA) allocates addresses to regional registries, who then allocate them to local registries or Internet service providers (ISPs). The purpose of Internet Society (ISOC) is to encourage the development and availability of the Internet. It provides organizational resources to the Internet Architecture Board (IAB). The Internet Assigned Numbers Authority (IANA) manages allocation of Internet Protocol (IP) addresses and maintenance of the top-level domain space.

Which layers of the Open System Interconnection (OSI) model make up the physical and logical topologies of network segments? (Select two). A. Layer 1 B. Layer 2 C. Layer 3 D. Layer 4

A and B Layer 1, Physical layer, is responsible for physical topology. Physical and Logical topologies create network segments within the Open System Interconnection (OSI) model. Layer 2, Data Link layer, determines how multiple nodes that are on the same physical segment can share access to the network media. This is referred to as the logical topology. Layer 3, Network layer, is responsible for moving data around a network of networks, known as an internetwork. Layer 4, Transport layer, has the critical function of identifying each type of network application by assigning it a port number.

Consider the features of Protocol Data Units (PDUs) and determine what role encapsulation performs during communications. A. Enables communication between nodes at the same layer B. Describes how data should be packaged C. Describes where data should go D. Enables systems to communicate by exchanging data

B Encapsulation describes how data should be packaged for transmission. The basic process of encapsulation is for the protocol to add fields in a header to the data it receives from an application or other protocol. Same layer interaction is communications between nodes at the same layer. At each layer, for two nodes to communicate, they must be running the same protocol. Addressing is the term used in Protocol Data Units (PDUs) for describing where data should go. A protocol is a set of rules that enable systems to communicate by exchanging data in a structured format.

A packet is being sent from Network 1 to Network 4. The shortest route is for the packet to use the path 1234. A router fails at Network 3 and the packet uses an alternate path of 1254. This scenario depicts the application of which of the following technology? A. Circuit-switched path B. Packet switching C. Circuit D. Fragmentation

B Packet switching provides the ability for one host to forward information to another using any available path. It is considered robust because it can automatically recover from communications link failures. A circuit-switched path is designed so that routers negotiate a link, then once the connection is established, all communications are forwarded along the same path. If this circuit were broken, the computers would stop communicating immediately. A circuit is a dedicated path established between two locations, such as two routers or two modems. Fragmentation is the capability of the Internet Protocol (IP) to divide large messages into numerous small packets meaning that a single packet can be resent at relatively little cost if it is lost or damaged during transmission.

Compare the Open System Interconnection (OSI) model and the Transmission Control Protocol/Internet Protocol (TCP/IP) protocol stack and determine which statements accurately distinguish between the two. (Select two). A. The TCP/IP protocol stack consists of 5 layers compared to the 7 layers found in the OSI model. B. The Application layer of TCP/IP consolidates Layers 5-7 of the OSI model. C. PPP, PPTP, and L2TP occur at the Link layer of the TCP/IP protocol stack and occur at Layer 2 of the OSI model. D. TCP and UDP occur at the Internet layer of the TCP/IP protocol stack.

B and C The Application layer of the Transmission Control Protocol/Internet Protocol (TCP/IP) protocol stack covers the Session (layer 5), Presentation (layer 6), and the Application (layer 7) of the Open System Interconnection (OSI) model. Point-to-Point Protocol (PPP), Point-to-Point Tunneling Protocol (PPTP), and Layer 2 Tunneling Protocol (L2TP) all occur at the Link layer of the TCP/IP protocol stack. The TCP/IP protocol stack consists of 4 layers (Link, Internet, Transport, and Application) compared to the 7 layers (Physical, Data Link, Network, Transport, Session, Presentation, and Application) found in the OSI model. Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) both occur at the Transport layer of the TCP/IP protocol stack.

Differentiate between the characteristics of a Local Area Network (LAN) and a Wide Area Network (WAN). A. A LAN is limited in size and typically has less than 1000 nodes while a WAN is unlimited in size. B. A WAN is limited in size and typically has less than 1000 nodes while a LAN is unlimited in size. C. A LAN is a network with one geographic location while a WAN is spread across multiple geographic locations with shared links. D. A WAN is a network with one geographic location while a LAN is spread across multiple geographic locations with shared links.

C A network in a single location is often described as a Local Area Network (LAN). Networks in different geographic locations with shared links are called Wide Area Networks (WANs). A LAN does not have a limit to the size of the network and can include residential networks with a couple of nodes to an enterprise network with thousands of nodes. A WAN does not have a limit to the size of the network. A WAN may consist of two locations, each containing a small number of nodes or consisting of hundreds of locations with thousands of nodes. A WAN is spread across several geographic locations with shared links while a LAN has a single geographic location.

Summarize the functions of the Link layer in the Transmission Control Protocol/Internet Protocol (TCP/IP) protocol stack. A. The Link layer establishes connections between the different applications that the source and destination hosts use to communicate. B. The Link layer is where many of the high level protocols can be run, such as File Transfer Protocol (FTP). C. The Link layer defines the host's connection to the network media and includes the hardware and software involved in the interchange of frames between hosts. D. The Link layer provides addressing and routing functions along with the ability to fragment large frames from the Network Interface layer into smaller packets.

C The Link layer defines the host's connection to the network media and includes the hardware and software involved in the interchange of frames between hosts. The Transport layer establishes connections between the different applications that source and destination hosts are communicating with. It breaks Application layer information into segments. The Application layer is the layer at which many Transmission Control Protocol/Internet Protocol (TCP/IP) services (high level protocols) can be run, such as File Transfer Protocol (FTP). The Internet layer provides addressing and routing functions. It also provides the ability to fragment large frames from the Network layer into smaller packets.

Evaluate the roles of Layer 1 and Layer 2 of the Open Systems Interconnection (OSI) model. Which of the following devices are part of Layer 2? (Select two) A. Hub B. Modem C. Bridge D. Network Interface Card

C and D Layer 2 is the Data Link layer. This layer is responsible for transferring data between nodes on the same logical segment. A bridge joins two network segments while minimizing the performance reduction. A Network Interface Card (NIC) joins a host to network media and enables it to communicate over the network by assembling and disassembling frames. Layer 1 is the Physical layer. A node is any device that can communicate on the network and can be used to describe endpoint devices or forwarding devices. A hub is a multiport repeater deployed as the central point of connection for nodes. A modem is a device that converts between digital and analog signal transmissions and is found at the Physical layer.

Summarize the role of Layer 6 in the Open System Interconnection (OSI) model. A. Provides an interface for software programs on network hosts that have established a communications channel B. Administers the process of establishing the dialog, managing data transfer, and then ending the session C. Moves data around an internetwork using logical network and host IDs D. Transforms data between the format required for the network and the format required for the application

D Layer 6 is known as the Presentation layer. This layer transforms data between the format required for the network and the format required for the application. The Application layer, Layer 7, provides an interface for software programs on network hosts that have established a communications channel to exchange data. The Session layer, Layer 5, represents the dialog control functions that administer the process of establishing the dialog, managing data transfer, and then ending the session. This can occur via simplex, half-duplex, or duplex. The Network layer, Layer 3, is responsible for moving data around a network of networks, known as an internetwork, using logical network and host IDs. The networks are often heterogeneous.