Introduction to TCP/IP fundamentals

Protocol - set of rules and guidelines that govern the communication between different devices.

Protocol stack - a layered set of protocols working together to provide a set of network functions. Each protocol/layer services the layer above by using the layer below.

TCP/IP began as an experiment by the Department of Defense to interconnect diverse computer systems.

The TCP/IP protocol suite is a standard set of protocols for the communication and interconnection of all types of computer systems.

The name is derived from the two most widely implemented protocols in the suite: Transmission Control Protocol (TCP) and Internet Protocol (IP).

IP - This is a connectionless protocol, which means that a session is not created before sending data. IP is responsible for addressing and routing of packets between computers. It does not guarantee delivery and does not give acknowledgement of packets that are lost or sent out of order as this is the responsibility of higher layer protocols such as TCP.

Internet Protocol (IP)
A Protocol that:
Addresses Packets
Routes Packets
Fragments and Reassembles Packets
Prevents Packets from Endlessly Looping Around a Network (TTL)

IP Addresses
Each computer on a TCP/IP network has to have a unique, numeric IP address.
The IP address is like a mailing address; some of the bits represent the network segment that the computer is on. That's like the street name of a mailing address. Other bits represent the particular host on the segment; that's like the house number.

IP Time To Live (TTL)
Prevents Packets from Endlessly Looping Around the Internet (TTL)
When a packet leaves a computer the TTL is set to a maximum of 256
Each router will decrease the TTL by one or more
If the TTL reaches Zero, the Router Sends the Source Computer a ICMP-Time Exceeded and discards the packet

TCP - Transmission Control Protocol - provides connection oriented, acknowledge, reliable transport services between end points.

Transmission Control Protocol (TCP):

Connection oriented – an acknowledgement (ACK) verifies that the host has received each segment of the message, reliable delivery service.
Before two computers communicate with TCP, they exchange configuration information through a three-way handshake.

TCP Provides Reliable Data Delivery
- Acknowledgements are sent by receiving computer
- Unacknowledged packets are resent
- Sequence number are used with acknowledgements to track successful packet transfer

Telnet, FTP, HTTP, and SMTP are examples of applications and protocols that use the TCP protocol.

UDP - User Datagram Protocol - provides same services as TCP but is connectionless and unacknowledged.

User Datagram Protocol (UDP).
lets applications send datagrams without the overhead involved in acknowledging packets and maintaining a virtual circuit. UDP is therefore used to broadcast messages across an internetwork, because acknowledgment is unnecessary and overhead is undesirable.

ARP - Address Resolution Protocol - handles IP address to hardware (MAC) address resolution

Address Resolution Protocol (ARP) Translates a host's software address to a hardware (or MAC) address (the node address that is set on the network interface card).

Reverse Address Resolution Protocol (RARP) Adapted from the ARP protocol and provides reverse functionality. It determines a software address from a hardware (or MAC) address. A diskless workstation uses this protocol during bootup to determine its IP address.

BOOTP Also used by diskless workstations. It enables these types of workstations to discover their IP addresses, the address of a server host, and the name of the file that should be loaded into memory and run at bootup.

DHCP - Dynamic Host Configuration Protocol - used to centrally administer the assignment of IP addresses, as well as other configuration information such as subnet masks and the address of the default gateway. When you use DHCP on a TCP/IP network, IP addresses are assigned to clients dynamically instead of manually.

Dynamic Host Configuration Protocol simplifies administration and extends Internet capabilities by loaning (or leasing) an IP number to a part time connection.

ICMP - Internet Control Message Protocol enables systems on a TCP/IP network to share status and error information such as with the use of PING and TRACERT utilities.

SNMP was designed to enable the analysis and troubleshooting of network hardware. For example, SNMP enables you to monitor workstations, servers, minicomputers, and mainframes, as well as connectivity devices such as bridges, routers, gateways, and wiring concentrators.

The two required components for managing a network using SNMP are SNMP Managers (or management systems) and SNMP Agents.

SNMP Managers request information from SNMP Agents concerning their current configuration, network activity, and statistics on performance.

Information requested of agents is located in a host's Management Information Base (MIB). The MIB is a database of information about defined objects, such as physical and network addresses, statistics, counters, and route and ARP tables.

Autonomous System

IP is well suited for big, complicated internetworks because it enables the division of an internetwork into logical groups called autonomous systems.

An autonomous system is a collection of networks (routers), administered by a single authority that use the same Interior Gateway Protocol (IGP) to route packets. In this case, router and gateway are interchangeable; routing protocols can be referred to as gateway protocols and vice versa.

For more information on Networking Basics, the OSI Model and Server Administration:
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