TCP/IP Suite Protocols and Networking Concepts

Origins of TCP/IP

• The U.S. Department of Defense (DOD) coordinated efforts that resulted in Transmission Control Protocol/Internet Protocol (TCP/IP).
• The Advanced Research Projects Agency (ARPA) was charged with creating a wide area network (WAN), resulting in TCP/IP and ARPANET.
• DOD funded projects to adapt TCP/IP to work with UNIX and include the TCP/IP protocol with Berkeley UNIX (BSD UNIX).

Overview of the TCP/IP Protocol Suite

• The TCP/IP model explains the protocol suite's operation for communications, with four layers: Application, Transport, Internetwork, and Network Interface.
• Requests for Comments (RFCs) define, describe, and standardize configuration and implementation of the TCP/IP protocol suite.

Application Layer

• Protocols at the TCP/IP Application layer include File Transfer Protocol (FTP), Trivial File Transfer Protocol (TFTP), and Network File System (NFS).
• Simple Mail Transfer Protocol (SMTP), Terminal emulation protocol (telnet), and Remote login application (rlogin) are also included in the Application Layer.
• Simple Network Management Protocol (SNMP), Domain Name System (DNS), and Hypertext Transfer Protocol (HTTP) are included in this layer.

Transport Layer

• Performs end-to-end packet delivery, reliability, and flow control.
• TCP provides reliable, connection-oriented communications between two hosts, requiring more network overhead.
• UDP provides connectionless datagram services between two hosts and is faster but less reliable, leaving reliability to the Application layer.

Transport Layer - Ports

• TCP and UDP use port numbers (1 to 65,535) for host communications.
• Well Known Ports range from 1 through 1,023.
• Registered Ports range from 1,024 through 49,151.
• Dynamic/Private Ports range from 49,152 through 65,535.

Transport Layer - TCP Three-Way Handshake

• Establishes a reliable connection between two endpoints
• TCP transmits three packets before data transfer occurs
• Computers synchronize initial sequence numbers (ISN) before communicating over TCP
• A reset packet (RST) indicates TCP connection termination

Transport Layer - TCP Sliding Windows

• TCP sliding windows control communication flow and efficiency, also known as windowing
• Allows multiple packets to be sent and affirmed with a single acknowledgment packet
• Window size determines the number of acknowledgments for a data transfer.
• Networks performing large data transfers should use large window sizes.
• Other flow control methods include buffering and congestion avoidance.

Internetwork Layer

• Functions at this layer include Internet Protocol (IP), Internet Control Message Protocol (ICMP), Address Resolution Protocol (ARP) and Reverse Address Resolution Protocol (RARP).
• ARP is a routed protocol that maps IP addresses to MAC addresses
• ARP tables store MAC and IP addresses of network devices

Internetwork Layer - ARP

• When a computer transmits a frame on the local network, it checks the ARP cache for an IP to MAC address mapping.
• An ARP request is sent if an IP to MAC address mapping cannot be located in the ARP table; the correct mapping must be obtained.
• A source computer broadcasts an ARP request to all hosts on the local segment.
• The host with the matching IP address responds to this request.
• A source checks its local ARP cache prior to sending packets on the local network.

Internetwork Layer - RARP

• RARP is reverse to ARP and used primarily by diskless workstations, which have MAC addresses but no IP addresses.
• A client's IP configuration is stored on a RARP server.
• ARP obtains the MAC address of other clients; RARP obtains the IP address of the local host.
• The local host maintains the ARP table, while a RARP server maintains the RARP table.
• The local host uses an ARP reply to update its ARP table and send frames to the destination.
• Routers filter broadcast traffic and the source forwards the frame to the router

Internetwork Layer - Ping and Trace Utilities

• Routers maintain ARP tables to transmit frames between networks, using ARP like other hosts.
• They include port numbers of their NICs in the ARP table because they have multiple network interfaces.
• The Packet Internet Groper (Ping) utility verifies connectivity between two points using ICMP echo request/reply messages.
• The Trace utility uses ICMP echo request/reply messages to verify Internetwork layer (OSI-Network layer) connectivity.
• It shows the exact path a packet takes from source to destination using the time-to-live (TTL) counter.
• Several malicious network attacks use ICMP messages like ICMP floods.

Network Interface Layer

• Plays the same role as the Data Link and Physical layers of the OSI model.
• Includes the MAC address, network card drivers, and specific interfaces for the network card.
• Has no specific IP functions; it focuses on communication with the network card and other networking hardware.

Frame Transmission

• Each host on a segment evaluates each frame to see whether the destination MAC address matches its own or is a broadcast to all hosts
• The host makes a copy of the frame and sends the original along the network path
• On the destination host, frames are sent up the TCP/IP stack, and each layer header information is removed.
• An IP address and MAC address are required for both the source and destination hosts for a packet to be routed on a TCP/IP internetwork.

Routers

• Routers require an IP address for every connected network segment and a separate network interface/port for each segment.
• Computers send frames to the router (default gateway) for destinations outside their segment.
• The router references its routing table to determine which subnet should receive the frame.

Network Configuration

• Routers maintain routing tables to route packets between networks.
• When a network uses TCP/IP, each router port requires an IP address, allowing appropriate packet forwarding.
• Logical addresses (IPs) must be matched on a TCP/IP segment; if a computer moves segments, its IP address must change.

Routing Tables

• Routing tables match network addresses with the routers' addresses.
• Tables can be built statically or dynamically, with dynamic routing updates provided through routing protocols.
• Dynamic routing allows a router to choose among routes and communicate with other dynamic routers.
• The two methods to determine the best path across a network are the distance-vector algorithm and the link-state algorithm

Transmitting Packets to Remote Segments

• When TCP/IP hosts transmit packets to remote segments, they contact their default gateway (usually a router).
• The router checks its routing tables against the destination IP address to locate the network interface for forwarding the packet.
• A router re-addresses frames or sends the packet to the next router in the path via indirect routing.

Cisco Three-Layer Hierarchical Model

• Describes network design without detailing communications, particularly for larger networks.
• Each layer is involved in specific functions, typically defined by a particular type of device.
• The three layers, from bottom up, are: Access, Distribution, and Core.

Access Layer

• The layer closest to the users, where they attach to the network.
• Could be a router if the network is very small but generally uses a hub or layer 2 switch.
• Deals with connecting workstations to the network.
• Frames are delivered to the users at this layer

Distribution Layer

• Separates the Access layer from the Core layer
• Implements network policies and provides networking services like Network Address Translation (NAT), firewall protection, and quality of service (QoS).
• IP addressing hierarchy is managed at this layer.
• Involves routers, including all router functions and almost all connectivity tasks.

Core Layer

• Responsible for switching large amounts of data quickly and efficiently
• Should not be burdened with security or traffic control measures or any unnecessary additional equipment.
• The primary device at this layer is a high-end layer 3 switch, essentially the backbone of the network.

Summary - Key Points

• TCP/IP is not only limited to transmission control and Internet protocols.
• The Defense Advanced Research Projects Agency (DARPA) started TCP/IP.
• TCP/IP maps to a four-layer network model: Application, Transport, Internetwork, and Network Interface.
• The Application layer in the TCP/IP model covers the Application, Presentation, and Session layers of the OSI reference model.
• TCP and UDP protocols reside at the Transport layer, using port numbers from 1 to 65,535.
• The Internet Protocol (IP) resides at the Internetwork layer.
• ARP/RARP reside in the Internetwork layer.
• MAC addresses are the final communication leg between the hosts.
• Ping utility (with IP and ICMP) diagnoses and troubleshoots connections.
• Routing tables can be created dynamically or statically.
• The Cisco Three-Layer Hierarchical model helps design efficient networks.

Explore essential protocols in the TCP/IP suite, including ICMP, TCP, UDP, and ARP. Understand packet transmission, network communication, and the role of ARPA. Learn about TCP sliding windows and connection termination processes.