Networking Protocols and Communications Notes PDF

# NETWORKS PROTOCOLS AND COMMUNICATIONS ## OSI MODEL - **Application layer (layer 1)** - PDU: Data - Protocols: HTTP, FTP, SMTP, DNS - Function: Provides network services directly to end-user applications for process-to-process communications - **Presentation layer (layer 6)** - P...

# NETWORKS PROTOCOLS AND COMMUNICATIONS ## OSI MODEL - **Application layer (layer 1)** - PDU: Data - Protocols: HTTP, FTP, SMTP, DNS - Function: Provides network services directly to end-user applications for process-to-process communications - **Presentation layer (layer 6)** - PDU: Data - Protocols: TLS, SSL - Function: Manages data representation and coding, ensuring data is in a readable format for the receiving application - **Session layer (layer 5)** - PDU: Data - Protocols: NetBIOS, PPTP - Junction: Manages sessions between applications, coordinating and maintaining connections - **Transport layer (layer 4)** - PDU: Segment - Protocols: TCP, UDP - Function: Ensures reliable or unreliable data transport between hosts providing flow control, error checking, and data segmentation - **Network Layer (layer 3)** - PDU: Packet - Protocols: IP, ICMP, ARP - Function: Routes packets across network by managing logical addressing and forwarding - **Data link layer (layer 2)** - PDU: Frame - Protocols: Ethernet, PPP - Function: Facilitates data transfer between devices on the same network segment, handling MAC addressing and error detection - **Physical layer (layer 1)** - PDU: Bits - Protocols: Ethernet, Wi-Fi, Bluetooth - Function: Transmits raw bits over a physical medium ## TCP/IP MODEL - **Application layer** - PDU: Data - Protocols: HTTP, FTP, DNS - Function: Combines OSI layers 5-7, handling high-level protocols and network services. - **Transport layer** - PDU: Segment - Protocols: TCP, UDP - Function: Manages end-to-end communication, error checking, and data segmentation. - **Internet layer** - PDU: Packet - Protocols: IP, ICMP, ARP - Function: Manages logical addressing, routing, and packet forwarding. - **Network Access layer** - PDU: Frame/Bits - Protocols: Ethernet, Wi-Fi - Function: Encompasses both the OSI Data link and Physical layers, focusing on frame transmission and network interface. ## OSI Model vs TCP/IP Protocol Suite vs TCP/IP Model | OSI Model | TCP/IP Protocol Suite | TCP/IP Model | |-------------------|----------------------------------|-----------------| | Application | HTTP, DNS, DHCP, FTP | APPLICATION | | Presentation | | | | Session | | | | Transport | TCP, UDP | Transport | | Network | IPv4, IPv6, ICMPv4, ICMPv6 | Internet | | Data Link | Ethernet, WLAN, SONET, SDH | NETWORK | | Physical | | ACCESS | ### Benefits of using a layered model: - Foster competition because products from different vendors can work together. - Provide a common language to describe networking functions and capabilities. # NETWORK ACCESS ## Unshielded Twisted Pair (UTP) and Shielded Twisted Pair (STP) - **Unshielded Twisted Pair** - Composed of pairs of wires twisted together without any shielding - Primarily used in Ethernet networks for data transmission - More susceptible to electromagnetic interference (EMI) than STP but is less expensive and easier to install - Commonly used for standard Ethernet cables in LANs - **Shielded Twisted Pair** - Similar to UTP but includes an additional shielding (foil or braided mesh) around the twisted pairs or entire cable. - The shielding helps reduce EMI and crosstalk, providing better performance in environments with high interference. - Typically more expensive and bulkier than UTP, which can make installation more challenging. - Suitable for environments with high EMI, such as industrial or data-intensive networks. ## Cut-through Switching - Cut-through switching is a switching method where the switch starts forwarding a packet as soon as it reads the destination address, without waiting to receive the entire packet. ### Characteristics: - **Offers lower latency** because the switch forwards the packet almost immediately, improving network speed. - **Can lead to increased errors** since corrupted packets are not identified before forwarding. - **Commonly used** in situations where speed is prioritized over error-detection, such as in high-performance or low latency networks. ## Cut-through Switching types: - **Fast forward:** fastest with minimal latency - **Fragment free:** checks the first 64 bytes # NETWORK LAYER ## Characteristics of IP: - **Connectionless:** IP does not establish a dedicated end-to-end encryption connection before data transmission, which keeps IP overhead low. - **Best effort delivery:** IP does not provide guarantees for packet delivery; it doesn't handle packet loss, errors, or sequencing. - **Media Independent:** IP works independently of the media it traverses; It does have a maximum PDU size, known as the MTU (Maximum Transmission Unit), which varies by media type. ## Introducing IPv6: - **Increased Address Space:** IPv6 uses 128-bit addresses significantly expanding the number of possible addresses compared to IPv4's 32-bit structure. - **Improved packet handling:** IPv6 has a simplified header format, which helps improve packet processing efficiently. - **Elimination of NAT:** IPv6's vast address space removes the need for NAT, providing better end-to-end connectivity. ## Host Forwarding Decisions: A host can send packets to: - **Itself:** Using the loopback address (127.0.0.1) for testing. - **Local Host:** if the destination is within the same network as the source. - **Remote Host:** for destinations on a different network, the host uses the default gateway to route the packet. - **Default Gateway:** Acts as a router for forwarding to other networks (if the destination is not on the same network as the source). The host doesn't need detailed routing knowledge; it simply forwards the packet to the gateway. # TRANSPORT LAYER ## Transport layer responsibilities: - **Tracking conversations:** The transport layer manages conversations between applications on different hosts - **Segmentation:** It divides large data into smaller segments for easier management and transport - **Application Identification:** Uses port numbers to ensure data reaches the correct application on a device - **Multiplexing:** Allows multiple conversations over a network by segmenting data, enabling various applications to use the network simultaneously. ## TCP Features: - **Establishing a Session:** Connection-oriented protocol - Ensures the application is ready to receive the data. - Negotiate the amount of traffic that can be forwarded at a given time. - **Reliable Delivery:** Ensuring that each segment that the source sends arrives at the destination. - **Same-Order Delivery:** Numbering and sequencing the segments guarantee reassembly into the proper order - **Flow Control:** Regulate the amount of data the source transmits. ## UDP features: - **Stateless (Connectionless):** No tracking - **Any segments lost are not resent** - **No session establishment** - **Does not inform the sender about resource availability** # APPLICATION LAYER ## Presentation Layer Functions: - **Data Formatting:** Converts data into a format the receiver can understand. - **Data Compression:** Reduces the size of data to save bandwidth - **Data Encryption:** Secures data by transforming it into a coded format for safe transmission. ## Application layer Protocols: - **DNS (Domain Name System):** Translates domain names into IP addresses. - **DHCP (Dynamic Host Configuration Protocol):** Assigns IP addresses to devices dynamically. - **SMTP (Simple Mail Transfer Protocol):** Used to send emails. - **POP (Post Office Protocol) and IMAP (Internet Message Access Protocol):** Retrieve emails from servers, with IMAP for commands and data. - **HTTP (Hypertext Transfer Protocol)/HTTPS (Hypertext Transfer Protocol Secure):** Governs web communications, with HTTPS adding encryption for security. ## Intro to DHCP: - **SLAAC (Stateless Address Autoconfiguration):** - **Router Advertisements (RAs):** Routers should send periodic ICMPv6 RA messages (about every 200 seconds) or in response to RA Solicitation messages from hosts. These RA messages provide necessary network information, such as the IPv6 prefix, default gateway, and optional configuration information - **RA Flags:** RA messages contain flags that guide hosts on how to obtain their address: - **A flag:** Instructs the host to use SLAAC to generate its own IPv6 address - **O flag:** Indicates that additional configuration information is available from a stateless DHCPv6 server - **M flag:** Directs the host to use a stateful DHCPv6 server to obtain an IPv6 address - **Address Creation:** With SLAAC, the host generates its IPv6 address by combining the network prefix from the RA message with a 64-bit interface identifier, which can either be randomly generated or based on the device's MAC address. - **Duplicate Address Detection:** To ensure uniqueness # NETWORK PLANNING AND DESIGN ## Factors to consider when buying a device: - **Cost** - **Speed and types of ports/interfaces:** Choose devices with the right type and number of ports, such as Ethernet or fiber, based on network requirements - **Expandability:** Devices come in fixed or modular configurations, with modular options offering greater flexibility for future growth. - **Operating system features and services:** Look for support for security features. ## Access Attacks: - **Password Attacks:** Methods include brute force attacks, Trojan horse programs - **Trust Exploitation:** Attackers exploit trust relationships between systems - **Port Redirection:** - **Man-in-the-middle:** # ROUTING CONCEPT - **Remote Routing/Network Routing:** - **Router Functionality:** Routers connect different IP networks and determine the best path to forward packets. - **Packet Forwarding Mechanisms:** - **Process Switching:** The router checks each packet individually, which is slower. - **Fast Switching:** Uses a cache to store net-next hop information, reducing lookup times. - **Cisco Express Forwarding:** Most efficient, using a FIB and adjacency tables to speed up packet forwarding. - **Default Gateways:** Hosts use a default gateway to communicate with devices on different IP networks, enabling the router to handle traffic. - **Routing Decisions:** Routers examine packets, de-encapsulate them, and re-encapsulate them for the next network interface. - **Routing Table:** - **Static Routes:** Manually configured, offering high security, but requiring manual updates. - **Dynamic Routing Protocols:** RIP, OSPF, and EIGRP automatically share network reachability. - **Load Balancing:** When multiple paths with identical metrics exist, routers use load balancing to distribute traffic, enhancing network performance. # STATIC ROUTING ## Why use static routing? - **Smaller networks:** Static routes are ideal for smaller networks that don't need frequent changes. - **Stub networks:** When connecting to a network with only one route or exit point, static routes offer a straightforward way to define paths. - **Single default route:** Simplifies the routing process on the router and minimizes routing table entries. ## Recursive lookup: Occurs when a router needs to determine the final exit interface to forward a packet. - **First lookup:** The router checks for the destination network to identify the next-hop IP. - **Second lookup:** Searches the routing table for the exit interface to reach this next-hop address.