Learning CCNA - Chapter 2: Introduction to TCP/IP

The Process/Application layer protocol

• Telnet - terminal emulation.
  
• FTP - listing and manipulating directories, typing file contents, and copying files between hosts. It can't execute remote files as programs.
• TFTP - stripped-down, stock version of FTP. Has no directory-browsing abilities, sending much smaller blocks of data than FTP, and no authentication (insecure).
  
• NFS - specializaing in file sharing. It allows two different types of file systems to interoperate.
• SMTP - is used to send email. POP3 is used to receive email.
• LPD - designed for printer sharing.
• X Window - designed for client/server operations
• SNMP - collects and manipulates valuable network information. It gathers data by polling the devices on the network from a management station at fixed or random intervals, requiring them to disclose certain information.
• DNS - resolves hostnames (FQDN)
• DHCP - assign IP addresses to hosts

The Host-to-Host layer protocol

Port Number:

•  Numbers below 1024 are considered well-known port numbers and are defined in RFC 3232.
•  Numbers 1024 and above are used by the upper layers to set up sessions with other hosts and by TCP to use as source and destination addresses in the TCP segment.
  

The Internet layer protocol

All network roads don’t lead to Rome—they lead to IP. And all the other protocols at this layer, as well as all those at the upper layers, use it.

•  Internet Protocol (IP) - RFC791
  
•  Internet Control Message Protocol (ICMP) - RFC 1256. They can provide hosts with information about network problems, e.g. router's memory buffer full, max hops reached for a packet, ping and traceroute.
  
•  Address Resolution Protocol (ARP) - find the hardware address from a known IP address.
  
•  Reverse Address Resolution Protocol (RARP) - discover IP address for diskless machines from the known MAC address.
  
•  Proxy ARP -advantage: it can be added to a single router on a network without disturbing the routing tables of all the other routers that live there too. Disadvantage: increase the amount of traffic on your network segment, and hosts will have a larger ARP table than usual in order to handle all the IP-to-MAC-address mappings.
  

           

Network addressing

Private IP Addresses

Network Address Translation (NAT) -  takes a private IP address and converts it for use on the Internet.