Lesson 7: TCP/IP Basics

I. Standardizing Networking Technology

Published in

The Cabin Coder

4 min readApr 7, 2015

diff companies have diff protocols
novel netware uses IPX/SPX
microsoft uses NetBIOS/NETBEUI
apple uses AppleTalk
UNIX uses TCP/IP
UNIX’s protocol won
microsoft’s software is called the IPX/SPX on NWLINK for Netware server, on the Network+ exam, this is usually the wrong answer

powerful bc packet is compatible with any type of network technology
the physical layer (LINK LAYER) is not part of the TCP/IP suite
ie, the Ethernet, cable modern, DSL
only account for the software layers
the higher you go up the model the more headers are stripped away until all that is left is data

the IP works at the Internet Layer
it takes date chunks from the Transport layer and add addressing to create the final IP packet

a full IP packet header has 14 diff fields but some of the important ones are here:
version = IPv4 or IPv6
header length = total size of the IP portion of the packet in words (32-bit) is displayed in hl field
DSCP = differentiated services code point contains data used by the bandwidth sensitive applications, for ex: voice over IP
time to live = routers on the internet are not perfect and sometimes create loops
TTL counter cannot start higher than 255, usu. starts at 128
protocol — usually TCP or UDP

transport layer determin if data moving btw two systems is connection-oriented or not
transmission control protocol — reliable
user datagram protocol — fast, not reliable
you cannot choose TCP or UDP, the web browerser uses tcp bc the app layer protocol HTTP is built upon TCP
ACK/NACK process or just ACK = rule for receiving and sending machines to acknowledge e/o’s presense
data is called “segments” at TCP, each has sequencing number

TCP HEADER

sequence number = used to assemble/disassemble data
ACK number = tracks the readiness of two communicating systems to send receive data
flags = give both sides detailed info about the state of conneciton
checksum = checks TCP header for errors

UDP HEADER

Create some way to use IP addresses that each LAN has its own uniq id
Interconnect al the LANs using routers and give those routers some way to use the network id to send packets to the right network
give each comp on the network some way to recognize if a packet is for the LAN or for a computer on the WAN

router connects individual LANs into a larger network
default gateway = needs an IP address on the LANs that it serves, so it can correctly route packets
most net admin config the LAN-side NIC on the default gateway the lowest host addr in net, usu the host ID of 1

every TCP/IP has a tool to tell the sending computer whether the dest. IP addr is local or long distance
subnet mask — string of binary number, 32 bits
ex: 11111111.11111111.11111111.00000000
octet to decimal is: 255.255.255.0
portion of the ip addr that aligns with ones is the subnet mask ID
portion of the ip addr that aligns with zeros is the host ID
the PC compares the dest. IP addr to its own IP addr using the subnet mask,
if the dest. ip addr matches the computer’s IP wherever there’s a 1 in the subnet mask, then the sending PC knows the dest. is local
if it is a local call, the sending computer sends a broadcast to grab the receiving computer’s MAC address susing the Address Resolution Protocol (ARP)
if the receiving computer is not a local machine, the sending computer sends an ARP request to the default gateway
by definition, all computers on the same network have the same subnet mask and network ID