Internetworking

• Heterogeneity is inevitable – no single network technology is the best for all needs
• Internet – connect physical networks & software to make the resulting system appear homogeneous
• Internet is formed by networks, routers, and host
• Router – a device used to connect 2 networks that may use different technologies
• A router can connect networks that have
• Different technology
• Different connection media
• Different address schemes
• Different address sizes
• Different frame formats
• Protocol software used in the internet is assigned by layers – one software module for each layer
• This set of modules is known as a “stack” or “protocol stack”
• Layering Principle – Software implementing layer N at the destination receives exactly the message sent by software implementing layer N at the source.

• The internet is a collection of networks, routers interconnecting networks, and hosts connected to networks

• Hosts send IP packets
• Routers forward IP packets to the destination
• Hosts receive IP packets and pass IP packets to corresponding application depending on the port number
• Port is part of the transport layer

TPC/IP Protocols

• Layers:
• Physical – basic network hardware
• Network interface
• Media access (MAC) format of packet and addressing
• NIC – network interface card
• Internet – facilitates the sending of packets across the internet (multiple routers)
• Transport – transport data from an application in one computer to an application in another computer. It does not need to be reliable
• Application – everything else
• Internet Protocol (IP)
• Implements layer 3 (internet)
• Defines
• Internet addressing
• Packet format
• Routing
• IP addressing
• Abstraction
• Independent of hardware addressing
• 4 bytes long (32 bits)
• Unique IP address for each network interface
• IP is unreliable – reliability is implemented in TCP
• However, the internet will do it’s best to deliver the packet. IP is a “best effort” delivery protocol
• IP was designed this way to be the “least common denominator” of the networking hardware available
• Has been implemented on Ethernet, token ring, serial lines, ATM, SNA, Pronet, Apple talk, FDDI, radio
• The RFCs (Request for Comments) are documents publicly available that describe the TCP/IP protocols
• There is an RFC for every IP implementation in every networking hardware available
• IP on Ethernet
• IP on serial line (PPP, SLRP)
• IP on ATM
• Etc.

IP Addressing

• It is just an abstraction
• You give a different number to every interface in a host
• 0 and 256 are reserved for broadcast
• Routers have 2 interfaces, so it will have 2 IP addresses
• Hosts that have more than 1 IP address (multiple NICs) are called multi-home hosts
• Hosts connected to the same network have the same prefix in the IP address
• IP address (4 bytes) is divided into two parts
• Prefix that identifies network
• Suffix that identifies host in that network
• A global authority assigns unique prefixes to the different networks
• A local administrator assigns a unique suffix to each host
• How big should the prefix be? There are different kinds of network numbers depending on the number of hosts that the network will have