part 3: internetworking internet architecture, addressing, encapsulation, reliable transport and the...
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Part 3: Internetworking
Internet architecture, addressing, encapsulation, reliable transport and
the TCP/IP protocol suite
Internetworking: concepts, architecture and protocols
Motivation, architecture, routers, TCP/IP protocols, internet reference
model
Motivation• A large organisation will use several
networking technologies• Inter-organisational communication is
significant• Universal service - any two computers
should be able to communicate• However, different network technologies
cannot just be wired together
Internetworking
• Interconnect heterogeneous networks and provide universal service– Hardware: routers connect different networks– Internet protocols: provide universal service by
creating a single virtual network
Internet architecture
• Although a single router can connect many networks, most organisations use multiple routers
Virtual network• The illusion
that there is a single universal network
Internetworking protocols
• The TCP/IP Internet Protocols– begun in the 1970s– The Internet has emerged into the public
domain in the 1990s– Controlled by the Internet Engineering Task
Force (IETF)
Internet Reference Model
Host computers
• TCP/IP used the term host computer to refer to any system that connects to an Internet and that runs applications
• Both hosts and routers use TCP/IP protocol software
IP: Internet protocol addresses
Uniform addressing, the IP address hierarchy, address classes, dotted
decimal notation, special addresses, routers and addresses, address
resolution
Uniform addressing
• Internet protocols deal in packets and provide uniform addressing
• The addressing scheme is defined in software and is used transparently by applications
• Internet addressing is specified in the IP protocol
• Each host is assigned a unique 32 bit address
The IP address hierarchy
• Each 32 bit address is divided into two parts– prefix: physical network to which the host is
attached - the network number– suffix: a host attached to a given physical network
• Prefixes are coordinated globally and suffixes locally
Classes of IP address
• Size of prefix and suffix determines maximum number of networks and maximum number of hosts per network
• IP defines different classes of address with different sized prefixes and suffixes
• The first four bits of the address specify its class
The five classes of IP address
Dotted decimal notation
• Makes it easier to for humans to use addresses (names are also possible)
Classes and dotted decimal
Division of the address space
• Public Internet network numbers are assigned by Internet Service providers (ISPs) and these are coordinated by the Internet Assigned Number Authority
An addressing example
Classless Addressing
• The Internet is running out of addresses• Allow division between prefix and suffix to appear at
an arbitrary boundary• Consider network with only 9 hosts
– Only need four bits for host suffix– Class C (smallest) address uses 8 bits for host suffix– Can subdivide a class C address into 16 addresses with a
28 bit prefix and 4 bit suffix• Extend dotted decimal notation
– 193.68.138.0/28, 193.68.138.16/28, …,193.68.138.240/28
Special IP addresses
Routers and IP addressing
• Routers are assigned two or more IP addresses
• So are multi-homed computers
Binding protocol addresses• An Internet packet passes through a series of
routers – each hop takes it over a particular network,
either to a specific computer on that network or to the next router
– in either case, the sending router has to map between the protocol (IP) address and a hardware address
– this is called address resolution
Address resolution techniques
• Table lookup• Closed-form computation• Message exchange
– send message to specific server computers– broadcast message, only the required computer
responds
Pros and cons of techniques
Address resolution protocol
• TCP/IP defines the Address Resolution Protocol (ARP) which defines the format of resolution requests and responses
• This technique is usually combined with local caching of hardware addresses
Dynamic Host Configuration Protocol (DHCP)
• Special DHCP server that assigns IP addresses to hosts
• Newly booted machine broadcasts a DHCP discover packet
• DHCP server sends back an IP address– Permanent IP addresses
• Manually assigned by administrator– Automatic IP address from a pool of addresses to be
allocated on demand• Leased for a finite period of time
DHCP Operation
• DHCP server does not need to be on the same network as the host
Summary
• Uniform addressing• Address classes• Dotted decimal notation• Classless addressing• Special IP addresses• Address resolution (ARP) and ssignment (DHCP)