CS402: Computer Communications and Networks

Read this introduction to the basic terms and technologies we will cover in this course, as well as a brief review of how the Internet and computer networks evolved over time.

This video covers the historical significance of the IETF in shaping the Internet. The IETF's origins were as a network working group in the late 1960s, before the Advanced Research Projects Agency Network (ARPANET) implementation. Vint Cerf and Bob Kahn were instrumental in developing TCP/IP and transitioning ARPANET to TCP/IP in 1983. In 1986, the IETF's mission was to address engineering challenges within the DoD Internet, which included ARPANET and the Military Network (MILNET). The Internet Activities Board (IAB) transformed into the Internet Architecture Board (IAB) in 1992, which brought about changes in the roles of the Internet Engineering Steering Group (IESG) and the Internet Research Task Force (IRTF). There was controversy surrounding the IAB's recommendation of IP version 7 (IPv7), which led to the restructuring of the IETF and IAB through the POISED Working Group.

This video discusses Internet-Drafts (I-Ds) and Requests for Comments (RFCs) in the context of the Internet Engineering Task Force (IETF). It explores the unrestricted accessibility of IETF documents and the legal guidelines governing their use and distribution. What are the roles of RFCs as live documents and permanent records? Review the specifics of document formats, translation permissions, and regulations for excerpt publication, and note the file naming conventions, various RFC categories, such as Best Current Practices and Internet Standards, and the emphasis on compatibility over strict adherence in the path to standardization.

This chapter serves as an introduction to networking as you link across time to review the development of standards and technologies that comprise today's wired and wireless information systems entangled in the Web. What is the difference between a service and a protocol? What is topology, and what is a transmission mode? What is the purpose of each?

Watch this video about network topology and the difference between logical and physical topologies. You should become familiar with network structures such as bus, ring, star, mesh, point-to-point, point-to-multipoint, and MPLS. You should be able to recognize and explain these topologies, including their characteristics and some real-world applications.

This video explores the various forms of physical transmission media utilized in communication networks, namely twisted pair cable, coaxial cable, and fiber optic cable. You should be able to distinguish between these media types, their core applications, the materials they are constructed from, and their specific purposes in network communication.

While watching this video, focus on understanding network devices and their functions. How do devices like hubs, repeaters, concentrators, and amplifiers extend data transmission distances within specific network domains? Modems convert digital to analog signals. Bridges facilitate traffic forwarding based on MAC addresses and network connectivity between topologies. Switches reduce collision domains and direct packets using MAC addresses, while advanced switches enhance security and routing capabilities. Routers connect networks and use routing protocols to determine data paths. Network segmentation limits exposure to threats and controls movement within the network.

Layers are the foundation for studying computer networks. You must understand how to work with layers to describe the flow of a data request to its destination and how the reverse occurs when the destination sends a response.

Watch this video on Wide Area Networks (WANs). Common WAN components are copper line drivers, demarcation points, and Network Interface Units (NIUs). WANs are used to connect LANs over long distances. Common WAN issues include Internet connectivity problems, DNS issues, and interface concerns. How these issues can be resolved and troubleshooted?

This section discusses how networked applications are built on top of the transport service. There are two main types of transport services: connectionless and connection-oriented. What are the similarities and differences between the two types of services?

Watch this video from 37:08 to 58:00. Focus on the three common guided media for data transmission: twisted pair, coaxial cable, and optical fiber. Note their key characteristics and applications. Consider the advantages and disadvantages of each medium in terms of data rates and distances they can cover. Think about when it might be more practical to use twisted pair for shorter distances, coaxial cable for medium distances, or optical fiber for long-distance, high-speed connections. Be able to identify the main differences between these media. What are some real-world scenarios where you might choose one over the others?

Read these lecture notes. As you read, pay attention to the history and different versions of the internetworking structure based on TCP/IP protocols.

As you read these sections, consider the following questions: Which came first, the OSI model or the TCP/IP model? Which layers in the OSI model appear to be missing in the TCP/IP stack? Where are they in the TCP/IP model?

This video explores the OSI model and its various layers, which are important in facilitating communication among networked devices. By the end of this presentation, you will be able to recognize and articulate the functions of the seven OSI model layers and understand their sequential order. Be sure to observe how these layers interact to ensure seamless communication.

As you read this section, consider these questions: What is the client-server model? What is the function of the client? Where does the server reside?

This section introduces the peer-to-peer model, which will be discussed further.

Peer-to-peer (P2P) communication allows direct communication between two parties, which bypasses the need for a middleman, such as a server. Using P2P, a message can be sent online to a friend, going straight to their device as if they were having a face-to-face conversation or using an audio telecommunications device. Pay attention to the history of P2P, beginning with Napster. Then, review the role P2P plays in Bitcoin, a digital currency. The big deal here is control. How is P2P data stored that allows for control, and how does this make it harder for others to access it without consent? Since P2P promotes independence and security, consider the industries that could benefit from P2P technology while watching the video.

As you read, try to answer the following question: how does the peer-to-peer model change or improve the client-server model discussed in the previous section?

To access a website, you need to know the website's IP address. IP addresses can be somewhat cumbersome and difficult to remember since they are simply four numbers separated by periods (for example, 120.755.3.9). The Domain Name System (DNS) is the application that has solved this problem by allowing us to use "human readable" names for websites. What is the domain name for your home page on your work, school, or home LAN? What is the IP address for each one? Which would you rather use, the IP address or the domain name?

DNS is a global network that translates domain names into IP addresses. The video explains how the DNS functions like a GPS for the Internet, where domain names are your destination and IP addresses are the coordinates guiding you to your destination. It also describes how DNS is crucial for Content Delivery Networks (CDNs) to deliver content efficiently by providing geographically relevant IP addresses. After viewing, consider the question: What is the effect on web navigation right after a DNS update occurs?

This section examines the e-mail application and explores two more popular protocols: SMTP and POP3. How does e-mail work? How long does it take for a message to reach its destination? Then what happens?

HTTP is a text-based protocol, in which the client sends a request and the server returns a response. Try browsing the links on this page, such as by navigating through this course, to see how this is accomplished.

This video introduces Simple Network Management Protocol (SNMP), which is critical for maintaining a network's health. It allows the collection, organization, and modification of data about network devices. SNMP agents, embedded in devices like routers and switches, send alerts and how these are structured within a Management Information Base (MIB). Pay particular attention to the transition from SNMPv1 and v2 to the more secure SNMPv3, noting the security mechanisms it introduces. How do the security features in SNMPv3 enhance the protocol's effectiveness in protecting network management activities?

Secure shell (SSH) is a protocol enabling a protected connection to another computer across an unsecured network. A good analogy of sending data over the internet without SSH is like placing information in an unlocked box that anyone could open. SSH secures the process by allowing the box to be locked so only the intended recipient can open it with a special key. Through SSH, data is encrypted to ensure that sensitive information remains confidential. The primary goal of SSH is to ensure that the data sent can only be read by the person intended to receive it. Why might it be important to use SSH when connecting to a computer remotely over a public network?

Ports act as access points for services, similar to phone extension numbers, while protocols are the languages used for communication between applications. This video covers some well-known ports and dynamic port assignments that enable multiple connections, such as FTP, TFTP, SNMP, Telnet, SSH, DNS, DHCP, RDP, and SMB, alongside their default port numbers, that will enhance your understanding of network communication and management.

Read this tutorial on how to make a simple network application program with a Python socket. 

These exercises further expand the key principles in this chapter. As a computer professional, you will enjoy the challenges and higher-level discussions in this section. For the novice, wander through the presentations and spend more time on the topics that are meaningful to you.

It will take a significant amount of time for you to finish these exercises. We recommend that you schedule 4 hours and attempt a few challenging exercises.

This section discusses the transport protocol in perfect and imperfect network service environments in terms of interactions with the Service Data Unit (SDU) at various stages of the transmission between sending and receiving nodes. What happens to your transmission when the environment is perfect? If your data gets corrupted by transmission errors, lost, reordered, or duplicated, then what happens? When something goes wrong, what mechanisms are used to repair impacted activity?

The UDP allows several applications running on a host to exchange SDUs with several other applications running on remote hosts. This section explores the checksum process and how the UDP accomplishes this multiprocessing.

Almost every Internet application relies on the TCP in the transport layer. In this section, you will discover how your favorite Internet activity exchanges data worldwide. Then, as you continue through this unit, you will be able to travel with your data as it streams to its destination and back.

As you read this section, make sure you can describe the three-way handshake used by TCP to establish a connection.

As you read this section, make sure you are able to identify and explain the two types of connection release.

This section covers TCP's mechanisms for reliable data transfer, including how sequence and acknowledgment numbers ensure data integrity and how window sizes manage the flow of data to prevent overloading the receiver. How do these elements work together to maintain a stable and ordered data transfer process? How do sequence numbers and acknowledgments enhance the reliability of TCP communication?

Read this section on the Nagle Algorithm. What two strategies does it provide for data transmission?

Read this section on TCP windows. How does a TCP window improve processing in the transport layer?

Follow the path in this section to see how the TCP retransmission timeout improves transport performance.

As you read this section, consider the following questions: What is the exponential back off and how does TCP use it? What is the delayed acknowledgment strategy in TCP? What is the fast retransmit heuristic as utilized by TCP? What is the SACK option?

TCP's congestion control is one of its best performance control features. This section explains this feature and how it improves performance in the transport layer.

Read this tutorial to understand congestion management at different levels: end-to-end, router assisted, and pricing based.

Watch this video up to 8:56 to learn about Stream Control Transmission Protocol (SCTP). SCTP is a versatile transport protocol designed to manage multimedia and stream traffic. It's important to distinguish SCTP from the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP). Pay particular attention to their respective orientations and levels of reliability. Additionally, familiarize yourself with SCTP's various service types, including process-to-process communication, multiple streams, and multihoming capabilities.

Watch this video up to 14:25 to learn about the vulnerabilities in the Real-Time Transport Protocol (RTP) used for streaming audio and video content over IP networks. Knowledge of RTP's architecture and the significance of using randomized sequence numbers and timestamps to improve security. The video gives a hands-on demonstration of a critical vulnerability within the Asterisk PBX system, where RTP sessions can be hijacked by packets with incorrect source information. This points out the need for packet validation in RTP implementations to prevent unauthorized access and to ensure secure communication.

Read this summary of the transport layer, which relies on TCP mechanisms to recover from the errors of the network layer. Review the strategies at each stage of the transmission.

These exercises further expand the key principles in this chapter. As a computer professional, you will enjoy the challenges and higher-level discussions in this section. If you are a novice, explore the presentations and spend more time on the topics that are meaningful to you.

The network layer includes the datagram and virtual circuit modes, the separation between the data plane and the control plane, and the algorithms used by routing protocols. As you read this section, it is important to understand the purpose of the router and the use of the packet in enabling you to send data and receive the response. How does the packet interact with the router?

What are the two internal organizations used in the network layer? When is each used? What is a datagram? This page explores how a datagram is used at the network level. Compare and contrast the datagram organization with the virtual circuit discussed in this section. The concept of hop-by-hop forwarding is in this section. What does this concept have to do with the routing table? What is the difference between the data and control planes?

This video explores the elements of the Network Layer, which is the OSI Model's third tier. The primary role of the Network Layer is to route datagrams across various subnetworks. What does it mean for the datagram transmission to be a connectionless message? Make sure you can distinguish between unicast and broadcast messaging. Ensure you know the function of routers when directing traffic between networks, the structure of datagrams (especially the header and the payload), which component carries the transmitted information, and the differences between the two prevalent Internet Protocol versions used today: IPv4 and IPv6.

The control plane maintains the routing table using three techniques: static routing, distance vector routing, and link state routing. As you explore each one in detail, note their advantages and disadvantages. How does each method deal with link and router failures?

As you read this section, ensure you understand what static routing is and its advantages and disadvantages.

What is distance vector routing? What are its advantages and disadvantages?

Read this section on link state routing and its advantages and disadvantages. How does link state routing handle link and routing failures?

Watch this video to learn about Dijkstra's algorithm, a fundamental concept in graph theory for finding the shortest path in graphs with non-negative weights. Think about how the algorithm determines the shortest path from a source to all vertices. It does this by updating the distances and by prioritizing the nearest vertex, and then it constructs a minimum path tree. The algorithm finds shortest paths but only when using non-negative weights. If negative weights are used, what are the consequences?

The Bellman-Ford algorithm is a powerful tool for finding the shortest paths in weighted graphs that can handle negative weight edges. A weighted graph can be represented by circles representing nodes and edges represented by lines between or connecting the nodes. Unlike Dijkstra's algorithm, Bellman-Ford accommodates graphs with negative weights by iterating N-1 times, where N is the number of vertices. Why can't the graph contain negative weight cycles? How does the algorithm compare with Dijkstra's in terms of speed and versatility? When might the slower speed of Bellman-Ford be a worthwhile trade-off for its broader applicability?

This section explores the Internet Protocol (IP) to discover how IP enables the applications running above the transport layer (UDP/TCP) to utilize any of the different datalink layers available.

This section discusses IP version 4 before exploring network addressing in more detail. What are two of the problems with IP version 4 that led to the development of the Classless Interdomain Routing (CIDR) architecture? How does CIDR improve the scalability of the IP routing system?

IPv4 addresses are notated using a dotted decimal format. The current IPv4 system lacks sufficient addresses for today's device volume. After you watch this video, can you explain the difference between public and private IPv4 address ranges and their allocation strategies? What are the functions of special addresses like 0.0.0.0, 127.0.0.1, and 255.255.255.255? Can you think of scenarios where IPv4 addresses are autoconfigured versus when they are leased? To better understand the autoconfiguration process, consider reviewing RFC 3927, which formalizes this protocol.

Read these pages for a deeper and more detailed understanding of the need and use of subnetting and supernetting. Make sure that you understand the exact subnet to which an address/mask combination belongs. Once you determine the exact subnet, make sure that you can name the first and last hosts on that subnet, as well as the network name and broadcast address. These are very important principles that need to be mastered.

Sometimes, a router or the destination host has to inform the sender of the packet of a problem that occurred while processing that packet. In the TCP/IP protocol suite, this reporting is done by the Internet Control Message Protocol (ICMP). How does the ICMP generate these messages?

As the popularity of the Internet grew exponentially, it became necessary for an expanded addressing architecture, IP version 6 (IPv6). This section discusses how IPv6 has resolved a number of routing issues while becoming the new standard.

ICMPv6 is the companion protocol for IPv6, just as ICMPv4 is the companion protocol for IPv4. ICMPv6 is used by routers and hosts to report problems when processing IPv6 packets. In addition, ICMPv6 is used when auto-configuring addresses. This section discusses messaging for IPv6.

What are middleboxes, and why do we need them?

Large corporations and government agencies prefer their networks to be private (that is, not seen on the Internet). This section explores the concept of private networks to learn how their need to communicate with the outside world and with specific machines under certain conditions has resulted in NAT: the mechanism that allows private networks to communicate openly with the outside world. How does NAT work?

Routing protocols are discussed in terms of two classifications: intradomain and interdomain. What are the differences between these classifications?

The initial group of routing protocols comprises intradomain routing protocols, also called interior gateway protocols or IGPs. These protocols are called intradomain because they facilitate information exchange within the same domain or network. Routers use these protocols to share information about reachable destinations within the domain. Intradomain routing protocols include the Routing Information Protocol (RIP), a distance vector protocol, and the Open Shortest Path First (OSPF) that uses link-state routing.

What is RIP? What are the features of the RIP protocol? How does RIP meet the objectives of intradomain routing? What are its weaknesses?

What is OSPF? What are the features of the OSPF protocol? How does OSPF meet the objectives of intradomain routing? What are its weaknesses? How is OSPF different from RIP?

What are the objectives of interdomain routing? What is the difference between transit and stub domains? What are some of the relationships you can expect to find in an interdomain routing policy?

How does BGP differ from the intradomain protocols RIP and OSPF you have studied? What messages might the BGP generate? What is router convergence? Why is router convergence necessary? How does the BGP handle router convergence?

Watch this video from 59:10 to 1:06:39 to learn about multicast networking and how it enables data to be sent to multiple specified recipients by using special IP addresses representing a group of hosts. This type of selective broadcasting is helpful for applications such as streaming media, where it is efficient for one source to transmit to many receivers, such as a live lecture being sent to online students. Why is multicast more efficient than unicast or broadcast in this scenario? What mechanisms allow a host to join or leave a multicast group, and how does the network keep track of the memberships? What is multicast's role in optimizing network traffic and managing bandwidth, particularly when the same data is sent to many users?

This video explores Quality of Service (QoS) and details strategies for network traffic prioritization. Flows are characterized by bandwidth, delay, jitter, and packet loss for traffic management. There are four primary QoS enhancement techniques and three scheduling methods that dictate packet transmission priorities. Traffic shaping and its two main algorithms are designed to regulate data flow and maintain network efficiency. Admission control and resource reservation are two crucial processes for managing network congestion and ensuring the availability of necessary resources.

These exercises expand the key principles in this unit. If you are a computer professional, you will enjoy the challenges and higher-level discussions in this section. If you are a novice, explore the presentations and spend more time on the topics that are meaningful to you.

This is a software tool that helps you perform networking experiments on your computer. If you'd like to explore it, download it and try it with a few simple examples.

If you'd like more practice, you can scan for network devices in your local area network using an app on your mobile device.

The datalink layer uses the service provided by each of the different technologies found in the physical layer to send and receive bits between directly connected devices. The datalink layer receives packets from the network layer. What are the two main services provided by the datalink layer? Why are these services necessary?

What is the framing problem? What service does the datalink layer provide to resolve this problem?

Datalink mechanisms also help solve problems related to detecting transmission errors.

A computer network environment faces additional problems beyond the framing and error detection issues that are resolved in the datalink layer. What are these problems? How do the Medium Access Control algorithms function in each computer network topology?

What is static allocation? What are some of the static allocation methods utilized in the datalink layer to share resources in a computer network? Make sure you can describe each method and how they handle the available resources.

The University of Hawaii addressed the problem of sharing resources with its network of remote island campuses in a unique way. This description of the ALOHAnet explores their solution.

ALOHAnet originated at the University of Hawaii in the early 1970s. This network revolutionized wireless networking with its innovative ALOHA random access method using UHF frequencies to enable communications between remote units and a central station without dedicated scheduling. The system began as Pure ALOHA and was later refined with Slotted ALOHA, which had enhanced efficiency using synchronized transmission timings that mitigated data collisions. This formed the foundational technology for Ethernet, Wi-Fi, and mobile technology using a system of random time intervals.

How did Reservation ALOHA (R-ALOHA) reduce network delays and support higher traffic levels? What mechanism allows stations to maintain control over specific slots after successful transmissions? Consider how the two-channel star configuration of ALOHAnet optimized network communication for interactive computing. This design choice has influenced contemporary network communication protocols and the efficient use of network resources.

CSMA enhanced the ALOHA solution. Make sure you can describe CSMA and how it works to share computer network resources.

In a wired environment, both ALOHA and CSMA performance are better able to detect collisions. Can you explain why that is?

CSMA/CA is found in the Wi-Fi environment. How are collisions avoided?

Some applications are sensitive to the time delay of transmissions. Deterministic Medium Access Control algorithms have been used to resolve this problem. Explore this section to see some of the deterministic algorithms.

It would take a library full of volumes to discuss all of the technologies used on the Internet. We have condensed this information into a discussion of six major categories. The following resources address the datalink services of these technologies.

The Point-to-Point Protocol (PPP) evolved from the Serial Line IP (SLIP) to facilitate reliable internet connectivity over direct links. PPP includes framing, option negotiation, and session authentication that ensures a secure structure for data transmission. Important features include a flag sequence framing and protocol identification, enabling versatile authentication methods through the Extensible Authentication Protocol (EAP). Why did PPP replace SLIP, and how does its frame structure support data integrity?

Read this section about MAC addresses, which are the datalink services found in an Ethernet environment.

Read this article to learn about the difference between the two current implementations of the Ethernet protocol. Pay attention to the differences in the frame format between the two, and make sure you can determine which type of frame is being received for a captured frame. As you read, focus on the historical development of Ethernet, its role in local area networks (LANs), and the significance of IEEE 802.3 standards. How has Ethernet evolved? How can you differentiate it from the IEEE 802.3 standards?

What is an Ethernet switch? How does it function in the datalink layer? How does it utilize Medium Access Control mechanisms?

Watch this video to see how SDN works at a high level.

The spanning tree protocol is a distributed standard switch used to reduce the network topology to a spanning tree by eliminating all cycles. Explore these examples to see how this technology processes frames in the datalink layer.

How do Ethernet switches create virtual LANs?

Read this section for a deeper look at how VLANs are implemented in networks and how switches react when they receive frames with a particular VLAN tag. How do switches direct frames based on VLAN tag, dropping or forwarding depending on VLAN members on a particular VLAN?

Wi-Fi is a very popular wireless networking technology. There are hundreds of millions of Wi-Fi devices, resulting in multiple wireless networking standards that use different frequency ranges and different physical layers. This section explores the wireless revolution in the datalink layer.

The Address Resolution Protocol (ARP) is a vital network function that translates IP addresses to MAC addresses. ARP comes into play when a network device, such as a host or router, needs to determine the MAC address associated with a known IP address in the same local network to facilitate direct communication. In this video, you will see how a device broadcasts an ARP request to retrieve the MAC address of another device. This process ensures that data is transmitted to the correct recipient. As you watch, consider the enhanced efficiency ARP provides to network operations. Be prepared to discuss the potential impact on data transmission if ARP were unavailable and the role ARP plays in directing data to the correct device in a network.

Read this summary of how Local Area Networks pose a problem for transporting frames when several devices share the same transmission channel. Various Medium Access Control algorithms have been necessary to regulate the access to the transmission channel by reducing collisions: ALOHA, CSMA, CSMA/CD, and CSMA/CA. Review these key technologies here.

Watch this video for more details about networking devices such as switches, hubs, and routers. A network switch is a multiport network bridge that uses hardware addresses to process and forward data at the data link layer (layer 2) of the OSI model. A router is a networking device that forwards data packets between computer networks. An Ethernet hub, active hub, network hub, repeater hub, multiport repeater, or simply "hub", is a network hardware device for connecting multiple Ethernet devices together and making them act as a single network segment.

These exercises expand on the key principles from this unit. If you are a computer professional, you will enjoy the challenges and higher-level discussions in this section. If you are a novice, explore the presentations and spend more time on the topics that are meaningful to you.

This is an optional assignment. Follow the steps in this document to practice controlling your computer from a mobile device.

This article discusses one of the most popular network applications: Voice over IP. There are several industry protocols for Voice over IP. One of the most popular and widely accepted is the IETF protocol SIP. As you read, pay special attention to the registering and calling process.

Watch this video from 4:04 to 34:12. It discusses Internet Protocol Television (IPTV), a technology that streams live TV over the Internet. Unlike regular streaming, IPTV requires a strong Internet connection that can simultaneously handle TV, Internet, and voice calls. IPTV uses specialized networks to maintain consistent quality.

Pay attention to how TV channels are converted into digital formats for transmission, the efficiency of multicast technology in sending streams to multiple viewers, and the importance of network management. The video demonstrates how multicast efficiently distributes TV content, which reduces internet load. What technologies support this infrastructure from the network to your living room? How does IPTV combine the reliability of traditional TVs with the versatility of the Internet?

Read this section and focus on DoS attacks, intrusion, hijacking, Web authentication attacks, and weaknesses in Internet architecture.

When you first used your computer to access the Internet, what was the first security technique you heard about? How does a firewall protect your system from the "evil-doers" lurking on the Internet?

As you watch this video, concentrate on virtualization and deployment models like private, community, public, and hybrid clouds. When is cloud computing beneficial, such as for businesses requiring scalability? When may it not be suitable due to regulatory or stability reasons? What needs do the service models SaaS, PaaS, and IaaS serve? Which deployment model fits certain business scenarios? How does virtualization support cloud computing?

Watch this video, which discusses the advantages and disadvantages of cloud computing and when it makes sense for companies to move to the cloud.

Read this article and make sure you can describe when and where authentication, authorization, and accounting (AAA) are used.

Authentication services act as the first line of defense to confirm identities through credentials like usernames and passwords. The AAA validates user access, authorizes resource use, and logs activity. The Remote Authentication Dial-In User Service (RADIUS) protocol manages remote access authentication. What are its security implications, particularly the potential risks of only encrypting passwords? What are the potential consequences of authentication failure?

Watch this video from 16:26 to 28:09. Consider the distinctions between TACACS+ and RADIUS. TACACS+ is the go-to for WAN environments, with its robust logging and TCP-based encryption encompassing the whole packet. RADIUS is UDP-based and is favored in LAN settings for its speed and selective encryption of user credentials.

TACACS+ is relatively complex, while RADIUS has a more straightforward configuration process and improved resource efficiency. Both protocols are compatible with various authentication methods and directory services, but TACACS+ typically stands out for comprehensive accounting. Is the complexity of TACACS+ justified by its benefits? How often do network professionals use debugging tools to scrutinize authentication logs and maintain network security?

Lightweight Directory Access Protocol (LDAP) manages and accesses directory information over a network. LDAP is structured hierarchically within the Directory Information Tree. How might this hierarchy influence the way you query and retrieve information?

LDAP communications are not encrypted by default. Therefore, while LDAP is useful for authentication and directory services, securing LDAP communications with SSL or TLS is essential due to its unencrypted nature. Why it might be crucial to implement SSL or TLS in LDAP interactions? What are the roles of directory schemas and query mechanisms?

Watch this video on TCP and reliable data delivery. Why does TCP divide a file into packets, and how do sequence numbers aid in reconstruction at the destination? Consider TCP's response to packet loss and the role of acknowledgments in ensuring complete data transfer. How does TCP determine when to resend packets, and how does the timeout mechanism deal with delayed or out-of-order packets? Each element of TCP's design is essential for the protocol's ability to deliver data reliably over the Internet.

If you want to practice, follow these steps, which will instruct you on using port-scanning techniques to administrate a large network.

Read this detailed description of VPNs and how they can be used to improve network security.

If you would like to practice, follow these steps to control your computer from a mobile device via Virtual Network Computing. Virtual Network Computing is a graphical desktop sharing system. It uses the Remote Frame Butter Protocol to control another computer remotely. Even if you choose not to try this activity, reading it can still be valuable since it explains the difference between RDP and VNC.

If you have a Windows computer, you can try following these steps to control your computer from a mobile device.