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CSCI 233 Internet Protocols Class 3 - PowerPoint PPT Presentation

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CSCI 233 Internet Protocols Class 3. David C. Roberts. First…a little review. Internet Protocol Principles . Good Citizen Principle Scarcest Internet Resource. Outline. Internet addresses Mapping IP addresses to physical addresses. Internet addressing. The Internet.

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CSCI 233 Internet Protocols Class 3

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Csci 233 internet protocols class 3

CSCI 233Internet Protocols

Class 3

David C. Roberts

First a little review

First…a little review

Internet protocol principles

Internet Protocol Principles

  • Good Citizen Principle

  • Scarcest Internet Resource



  • Internet addresses

  • Mapping IP addresses to physical addresses

Internet addressing

Internet addressing

The internet

The Internet

  • Is it a physical or virtual network?

  • It’s a virtual network, defined by protocols that run on hosts and routers.

  • Internet protocols make the Internet look like a world-wide uniform network, although it encompasses many networks that are very different from each other.

Internet addresses

Internet Addresses

  • Each host connection on the Internet has a unique Internet address

  • The addresses are designed to make forwarding of Internet packets simple

  • An IP address has two parts: a prefix that identifies a network and a suffix that identifies a host on the network

Need for control

Need for Control

  • To avoid conflicts in address use, some sort of authority is needed

  • It makes sense to assign addresses in blocks, not one at a time

  • ICANN (Internet Corporation for Assigned names and Numbers) oversees IP address assignment

  • Originally assigned in blocks of Class A, B and C addresses



  • How many Internet addresses can one host have?

  • As many as it has network adapters

Ipv6 addressing

IPv6 Addressing

  • Each address is 128 bits

  • Enough addresses for every person on earth to have an internet with three times the addresses of the present Internet!

  • 1024 addresses per square meter of the earth’s surface

Ipv6 address assignments

IPv6 Address Assignments

Ipv4 to ipv6 transition

IPv4 to IPv6 Transition

Ipv6 address split

IPv6 Address Split

Ipv6 and mac addresses

IPv6 and MAC Addresses

Ip addresses

IP Addresses

Functions of internet addresses

Functions of Internet Addresses

  • Provide a unique identification for a particular interface between a device and the network so that a datagram can be delivered to the correct recipient

  • Enable a path to be found across the Internet to reach the recipient, a process called routing

Ipv4 address

IPv4 Address

  • 32-bit integer, unique for each host on the network, used in all communication with the host

  • <IP address> ::= <netid> <hostid>

    • Netid: identifier of a network

    • Hostid: identifier of a host on the network

Dotted decimal notation

Dotted Decimal Notation

32-bit Internet address

10000000 00001010 00000010 00011110

Is written

Classes of ipv4 addresses

Classes of IPv4 Addresses

“Classful” addresses—types A, B and C below

first 2 bits distinguish 3 primary classes

Design of these classes is for efficient routing

There have been other refinements—to discuss later

Class determination algorithm

Class Determination Algorithm

Address class characteristics

Address Class Characteristics

Host capacities

Host Capacities

Ip address split

IP Address Split

Advantages of classful addressing

Advantages of Classful Addressing

  • Simplicity and clarity—addresses and their setup are very easy to understand

  • Flexibility to accommodate different sizes of networks

  • Ease of separating host address for routing

  • Allows for reservation of some addresses for special purposes

Classless ipv4 addressing

Classless IPv4 Addressing

  • Temporary addressing scheme that does away with class A, B, C addresses

  • Network prefix can be any specified length

  • Forwarding techniques expanded to account for this: called Classless Inter-Domain Routing (CIDR)

Special ip addresses

Special IP Addresses

Cidr slash notation

CIDR Slash Notation

Address resolution

Address resolution

Ip and mac addresses

IP and MAC Addresses

  • IP address is used to send datagrams across the Internet—that is, between networks, through routers

  • MAC address is used to deliver a frame of data within a single network

  • We send a datagram across the Internet with only an IP address

  • To deliver to a device at the destination network, a MAC address must be used

Local delivery

Local Delivery

  • The router at the destination network has the job of delivering the packet to the appropriate host

  • The router uses the local physical network to deliver to the local host

  • The local physical (MAC) address must be used, not the IP address

Address resolution1

Address Resolution

  • The process of determining the physical address that corresponds to an IP address is called address resolution

  • Address resolution must occur at every network the packet encounters in its journey across the Internet

Resolution by direct mapping

Resolution by Direct Mapping

HA = f(IA)

Resolution by dynamic binding

Resolution by Dynamic Binding

  • ARP broadcasts a request packet

  • Host who has IP address in packet replies with physical address

Arp caching

ARP Caching

  • Broadcasting an inquiry is expensive

  • Every host must have a cache of recently acquired bindings

  • Results of ARP requests are cached

  • Before sending request, the cache is checked

Arp cache timeout

ARP Cache Timeout

  • Responsibility for cache correctness is with the host maintaining the cache

  • Timeout value is set, and addresses from cache are not used if timeout value is exceeded

  • ARP performance is sensitive to the value of the timeout

Soft state

Soft State

  • ARP cache is an example of “soft state”

  • Cache owner keeps record of acquired results, avoids cost of future inquiries

  • Cache is usually timed out to automatically remove stale values

Arp refinements

ARP Refinements

  • Every ARP request has binding of source IP and MAC addresses

  • Since request is broadcast, all machines can extract sender’s IP to MAC address mapping and cache it

  • Most computers broadcast a gratuitous ARP request when they start up in case their mapping has changed

Ipv6 arp


  • Describe IPv6 ARP

  • There isn’t any!!!

Ipv4 arp message format

IPv4 ARP Message Format

Hardware type: 1 for Ethernet

Protocol type: 0800 for IP addresses

Xlen—length of physical and high-level addresses

ARP exchanges involve filling in missing addresses

Ipv6 neighbor discovery

IPv6 Neighbor Discovery

  • Neighbor is another computer on the same network

  • NDP allows an IPv6 host to discover all neighbors and routers upon startup

  • Early binding avoids delays when packets are transmitted



  • 1’s refer to “all”

  • 0’s refer to “this”

  • Hostid=0 address refers to this network

  • Hostid=1’s broadcast to all hosts

    • Directed broadcast—netid of a specific network

    • Local broadcast—32 1’s—used at startup

Address resolution2

Address Resolution

  • Physical addresses are used by hardware devices that can communicate directly (ie, MAC addresses on a LAN)

  • IP addresses create a massive virtual network

  • Network layer sends datagrams across the virtual network

  • Data link layer sends frames between physical devices

Need for address resolution

Need for Address Resolution

Csci 233 internet protocols class 3


  • Each host has an Internet address, Ia

  • Each host also has a physical address, Pa

  • How to route packet to physical address, given its Internet address?

  • Two instances

    • Sending packets to routers, which have physical addresses

    • Sending packets to hosts, which have physical addresses

Direct mapping resolution

Direct Mapping Resolution

  • Choose a numbering scheme that makes address resolution efficient

    PA = f(IA)

  • If either P’s or I’s can be chosen, a correspondence can be established

  • Alternatively, lists of P-A pairs can be stored

Dynamic binding resolution

Dynamic Binding Resolution

ARP—Address Resolution Protocol

  • host A broadcasts packet with address IB

  • Asks host B to respond with PB

  • B recognizes the packet, responds with PB

  • A receives response, uses PB to send to B

Arp cache

ARP Cache

  • Cache of recently-acquired physical addresses is kept

  • ARP is used for packets after the first in a transmission

  • ARP cache times out after an interval

  • Example of “soft state”

Arp refinements1

ARP Refinements

  • Sender includes its own I to P binding in every ARP broadcast, so that receiving site, and others, can update ARP caches

  • Receivers update I to P binding in ARP cache before processing ARP packet

Arp encapsulation

ARP Encapsulation

Internet protocol principles1

Internet Protocol Principles

  • Use the Good Citizen Principle to limit the impact of resource shortages

  • Conserve the scarcest Internet resource

  • Use caching to avoid repeated inquiries



  • IP Addressing

  • IP Address Resolution

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