0
Internetworking
              With TCP/IP

                      Douglas Comer

             Computer Science Department
 ...
PART I

                               COURSE OVERVIEW
                                     AND
                          ...
Topic And Scope



Internetworking: an overview of concepts, terminology, and
technology underlying the TCP/IP Internet pr...
You Will Learn

d Terminology (including acronyms)
d Concepts and principles
       –      The underlying model
       –  ...
You Will Learn
                                              (continued)

d Internet architecture and routing
d Applicatio...
What You Will NOT Learn

d A list of vendors, hardware products, software products,
  services, comparisons, or prices
d A...
Schedule Of Topics

d Introduction
d Review of
       –      Network hardware
       –      Physical addressing
d Internet...
Schedule Of Topics
                                              (continued)

d Routing update protocols
d Application-lay...
Why Study TCP/IP?

d The Internet is everywhere
d Most applications are distributed




Internetworking With TCP/IP vol 1 ...
Remainder Of This Section

d History of Internet protocols (TCP/IP)
d Organizations
d Documents




Internetworking With T...
Vendor Independence

d Before TCP/IP and the Internet
       –      Only two sources of network protocols
              * ...
Who Built TCP/IP?

d Internet Architecture Board (IAB)
d Originally known as Internet Activities Board
d Evolved from Inte...
Components Of The
                                     IAB Organization

d IAB (Internet Architecture Board)
       –     ...
Components Of The
                                     IAB Organization
                                              (con...
ICANN

d Internet Corporation for Assigned Names and Numbers
                                         http://www.icann.org...
ICANN

d Internet Corporation for Assigned Names and Numbers
                                         http://www.icann.org...
World Wide Web Consortium

d Organization to develop common protocols for World Wide
  Web
d Open membership
d Funded by c...
Internet Society

d Organization that promotes the use of the Internet
d Formed in 1992
d Not-for-profit
d Governed by a bo...
Protocol Specifications
                                    And Documents

d Protocols documented in series of reports
d Do...
RFCs

d Series of reports that include
       –      TCP/IP protocols
       –      The Internet
       –      Related tec...
RFCs

d Series of reports that include
       –      TCP/IP protocols
       –      The Internet
       –      Related tec...
RFCs
                                              (continued)

d Numbered in chronological order
d Revised document reiss...
Requirements RFCs

d Host Requirements Documents
       –      Major revision/clarification of most TCP/IP protocols
      ...
Special Subsets Of RFCs

d For Your Information (FYI)
       –      Provide general information
       –      Intended for...
A Note About RFCs

d RFCs span two extremes
       –      Protocol standards
       –      Jokes
d Question: how does one ...
TCP/IP Standards (STD)

d Set by vote of IETF
d Documented in subset of RFCs
d Found in Internet Official Protocol Standar...
Internet Drafts

d Preliminary RFC documents
d Often used by IETF working groups
d Available on-line from several reposito...
Obtaining RFCs And
                                    Internet Drafts

d Available via
       –      Email
       –      ...
Summary

d TCP/IP is vendor-independent
d Standards set by IETF
d Protocol standards found in document series known as
  R...
Questions?
PART II

                           REVIEW OF
                    NETWORK HARDWARE AND
                      PHYSICAL ADDR...
The TCP/IP Concept

d Use existing network hardware
d Interconnect networks
d Add abstractions to hide heterogeneity




I...
The Challenge

d Accommodate all possible network hardware
d Question: what kinds of hardware exist?




Internetworking W...
Network Hardware Review

d We will
       –      Review basic network concepts
       –      Examine example physical netw...
Two Basic Categories
                                Of Network Hardware

d Connection oriented
d Connectionless




Inter...
Connection Oriented
                       (Circuit Switched Technology)

d Paradigm
       –      Form a ‘‘connection’’ t...
Connectionless
                       (Packet Switched Technology)

d Paradigm
       –      Form ‘‘packet’’ of data
     ...
Broad Characterizations Of
                          Packet Switching Networks

d Local Area Network (LAN)
d Wide Area Net...
Local Area Networks

d Engineered for
       –      Low cost
       –      High capacity
d Direct connection among compute...
Wide Area Networks
                                 (Long Haul Networks)

d Engineered for
       –      Long distances
  ...
Examples Of Packet
                                    Switched Networks

d Wide Area Nets
       –      ARPANET, NSFNET, ...
ARPANET (1969-1989)

d Original backbone of Internet
d Wide area network around which TCP/IP was developed
d Funding from ...
NSFNET (1987-1992)

d Funded by National Science Foundation
d Motivation: Internet backbone to connect all scientists and
...
ANSNET (1992-1995)




                                                   End-User Site
                                  ...
Wide Area Networks Available
                        From Common Carriers

d Point-to-point digital circuits
       –     ...
Example Local Area
                                    Network: Ethernet

d Extremely popular
d Can run over
       –     ...
Ethernet Frame Format
                      Destination    Source      Frame
        Preamble       Address       Address ...
Example Ethernet Frame In Memory

                   02 07 01 00 27 ba 08 00 2b 0d 44 a7 08 00 45 00

                   0...
Point-to-Point Network

d Any direct connection between two computers
       –      Leased line
       –      Connection b...
Hardware Address

d Unique number assigned to each machine on a network
d Used to identify destination for a packet




In...
Hardware Address Terminology

d Known as
       –      MAC (Media Access Control) address
       –      Physical address
 ...
Use Of Hardware Address

d Sender supplies
       –      Destination’s address
       –      Source address (in most techn...
Three Types Of Hardware
                             Addressing Schemes

d Static
       –      Address assigned by hardwa...
Examples Of Hardware Address Types

d Configurable: proNET-10 (Proteon)
       –      8-bit address per interface card
    ...
Examples Of Hardware Address Types
                                              (continued)

d Static MAC addressing: Eth...
Bridge

d Hardware device that connects multiple LANs and makes
  them appear to be a single LAN
d Repeats all packets fro...
Bridge
                                              (continued)

d Watches packets to learn which computers are on which
...
Layer 2 Switch

d Electronic device
d Computers connect directly
d Applies bridging algorithm
d Can separate computers ont...
Physical Networks As
                                   Viewed By TCP/IP

d TCP/IP protocols accommodate
       –      Loc...
The Motivation For Heterogeneity

d Each network technology has advantages for some
  applications
d Consequence: an inter...
Heterogeneity And Addressing

d Recall: each technology can define its own addressing
  scheme
d Heterogeneous networks imp...
Summary

d TCP/IP is designed to use all types of networks
       –      Connection-oriented
       –      Connectionless
...
Summary
                                              (continued)

d Each technology defines an addressing scheme
d TCP/IP ...
Questions?
PART III

               INTERNETWORKING CONCEPT
               AND ARCHITECTURAL MODEL




Internetworking With TCP/IP vo...
Accommodating Heterogeneity

d Approach 1
       –      Application gateways
       –      Gateway forwards data from one ...
Desired Properties

d Universal service
d End-to-end connectivity
d Transparency




Internetworking With TCP/IP vol 1 -- ...
Agreement Needed To
                           Achieve Desired Properties

d Data formats
d Procedures for exchanging info...
The TCP/IP Internet Concept

d Use available networks
d Interconnect physical networks
       –      Network of networks
 ...
Network Interconnection

d Uses active system
d Each network sees an additional computer attached
d Device is IP router (o...
Illustration Of
                              Network Interconnection


                                     Net 1    R   ...
Building An Internet

d Use multiple IP routers
d Ensure that each network is reachable
d Do not need router between each ...
Example Of Multiple Networks


                  Net 1                 R2    Net 2   R2   Net 3




d Networks can be hete...
Physical Connectivity


In a TCP/IP internet, special computers called IP routers or IP
gateways provide interconnections ...
Packet Transmission Paradigm

d Source computer
       –      Generates a packet
       –      Sends across one network to...
An Important Point
                                    About Forwarding


Routers use the destination network, not the des...
Equal Treatment


The TCP/IP internet protocols treat all networks equally. A
Local Area Network such as an Ethernet, a Wi...
User’s View Of Internet

d Single large (global) network
d User’s computers all attach directly
d No other structure visib...
Illustration Of User’s View Of
                              A TCP/IP Internet




                                       ...
Actual Internet Architecture

d Multiple physical networks interconnected
d Each host attaches to one network
d Single vir...
The Two Views Of
                                     A TCP/IP Internet




                        user’s view           ...
Architectural Terminology

d End-user system is called host computer
       –      Connects to physical network
       –  ...
Many Unanswered Questions

d Addressing model and relationship to hardware addresses
d Format of packet as it travels thro...
Summary

d Internet is set of interconnected (possibly heterogeneous)
  networks
d Routers provide interconnection
d End-u...
Questions?
PART IV

           CLASSFUL INTERNET ADDRESSES




Internetworking With TCP/IP vol 1 -- Part 4      1      2005
Definitions

d Name
       –      Identifies what an entity is
       –      Often textual (e.g., ASCII)
d Address
       – ...
Internet Protocol Address
                                  (IP Address)

d Analogous to hardware address
d Unique value a...
IP Address Details

d 32-bit binary value
d Unique value assigned to each host in Internet
d Values chosen to make routing...
IP Address Division

d Address divided into two parts
       –      Prefix (network ID) identifies network to which host
   ...
Classful Addressing

d Original IP scheme
d Explains many design decisions
d New schemes are backward compatible




Inter...
Desirable Properties Of An
                         Internet Addressing Scheme

d Compact (as small as possible)
d Univers...
Division Of Internet Address
                           Into Prefix And Suffix

d How should division be made?
       –     ...
Original IPv4 Address Classes

                                0 1              8           16      24        31
         ...
Important Property

d Classful addresses are self-identifying
d Consequences
       –      Can determine boundary between ...
Endpoint Identification



Because IP addresses encode both a network and a host on that
network, they do not specify an in...
IP Address Conventions

d When used to refer to a network
       –      Host field contains all 0 bits
d Broadcast on the l...
Assignment Of IP Addresses

d All hosts on same network assigned same address prefix
       –      Prefixes assigned by cent...
Advantages Of Classful Addressing

d Computationally efficient
       –      First bits specify size of prefix / suffix
d All...
Directed Broadcast



IP addresses can be used to specify a directed broadcast in
which a packet is sent to all computers ...
Limited Broadcast

d All 1’s
d Broadcast limited to local network only (no forwarding)
d Useful for bootstrapping




Inte...
All Zeros IP Address

d Can only appear as source address
d Used during bootstrap before computer knows its address
d Mean...
Internet Multicast

d IP allows Internet multicast, but no Internet-wide multicast
  delivery system currently in place
d ...
Consequences Of IP Addressing

d If a host computer moves from one network to another, its
  IP address must change
d For ...
Multi-Homed Hosts And Reliability
                                              NETWORK 1


                              ...
Dotted Decimal Notation

d Syntactic form for expressing 32-bit address
d Used throughout the Internet and associated lite...
Example Of Dotted Decimal
                                  Notation

d A 32-bit number in binary

                     10...
Loopback Address

d Used for testing
d Refers to local computer (never sent to Internet)
d Address is 127.0.0.1




Intern...
Classful Address Ranges
                             Class        Lowest Address   Highest Address
                       ...
Summary Of Address Conventions

                                        all 0s                              This host 1


...
An Example Of IP Addresses
                                              ETHERNET
                                        ...
Example Host Addresses
                                               ETHERNET 128.10.0.0




                            ...
Another Addressing Example

d Assume an organization has three networks
d Organization obtains three prefixes, one per netw...
Illustration Of IP Addressing
                                              Rest of the Internet

                        ...
Summary

d IP address
       –      32 bits long
       –      Prefix identifies network
       –      Suffix identifies host
...
Summary
                                              (continued)

d Special forms of addresses handle
       –      Limit...
Questions?
PART V

             MAPPING INTERNET ADDRESSES
               TO PHYSICAL ADDRESSES
                        (ARP)




Int...
Motivation

d Must use hardware (physical) addresses to communicate
  over network
d Applications only use Internet addres...
Example

d Computers A and B on same network
d Application on A generates packet for application on B
d Protocol software ...
Consequence

d Protocol software needs a mechanism that maps an IP
  address to equivalent hardware address
d Known as add...
Address Resolution

d Performed at each step along path through Internet
d Two basic algorithms
       –      Direct mappi...
Direct Mapping

d Easy to understand
d Efficient
d Only works when hardware address is small
d Technique: assign computer a...
Example Of Direct Mapping

d Hardware: proNet ring network
d Hardware address: 8 bits
d Assume IP address 192.5.48.0 (24-b...
Dynamic Binding

d Needed when hardware addresses are large (e.g., Ethernet)
d Allows computer A to find computer B’s hardw...
Internet Address Resolution Protocol (ARP)

d Standard for dynamic address resolution in the Internet
d Requires hardware ...
ARP

d Machine A broadcasts ARP request with B’s IP address
d All machines on local net receive broadcast
d Machine B repl...
Illustration Of ARP
                        Request And Reply Messages


                                       A         ...
ARP Packet Format When
                             Used With Ethernet

             0                        8           ...
Observations About Packet Format

d General: can be used with
       –      Arbitrary hardware address
       –      Arbit...
Retention Of Bindings

d Cannot afford to send ARP request for each packet
d Solution
       –      Maintain a table of bi...
ARP Caching

d ARP table is a cache
d Entries time out and are removed
d Avoids stale bindings
d Typical timeout: 20 minut...
Algorithm For Processing
                                  ARP Requests

d Extract sender’s pair, (IA, EA) and update loca...
Algorithm Features

d If A ARPs B, B keeps A’s information
       –      B will probably send a packet to A soon
d If A AR...
Conceptual Purpose Of ARP

d Isolates hardware address at low level
d Allows application programs to use IP addresses




...
ARP Encapsulation

d ARP message travels in data portion of network frame
d We say ARP message is encapsulated




Interne...
Illustration Of ARP Encapsulation

                                                    ARP MESSAGE




                   ...
Ethernet Encapsulation

d ARP message placed in frame data area
d Data area padded with zeroes if ARP message is shorter
 ...
Reverse Address Resolution Protocol

d Maps Ethernet address to IP address
d Same packet format as ARP
d Intended for boot...
Summary

d Computer’s IP address independent of computer’s hardware
  address
d Applications use IP addresses
d Hardware o...
Summary
                                              (continued)

d Address Resolution Protocol (ARP) used for dynamic
  ...
Questions?
PART VI

                  INTERNET PROTOCOL:
               CONNECTIONLESS DATAGRAM
                       DELIVERY




I...
Internet Protocol

d One of two major protocols in TCP/IP suite
d Major goals
       –      Hide heterogeneity
       –   ...
The Concept


IP allows a user to think of an internet as a single virtual
network that interconnects all hosts, and throu...
Internet Services
                                   And Architecture
                                  Of Protocol Softwa...
IP Characteristics

d Provides connectionless packet delivery service
d Defines three important items
       –      Interne...
Internet Packet

d Analogous to physical network packet
d Known as IP datagram




Internetworking With TCP/IP vol 1 -- Pa...
IP Datagram Layout

              DATAGRAM HEADER                     DATAGRAM DATA AREA




d Header contains
       –   ...
Datagram Header Format

           0            4             8                     16          19          24            ...
Addresses In The Header

d SOURCE is the address of original source
d DESTINATION is the address of ultimate destination

...
IP Versions

d Version field in header defines version of datagram
d Internet currently uses version 4 of IP, IPv4
d Precedi...
Datagram Encapsulation

d Datagram encapsulated in network frame
d Network hardware treats datagram as data
d Frame type fi...
Datagram Encapsulation For Ethernet


                                              IP HEADER               IP DATA




  ...
Datagram Encapsulated In Ethernet Frame

                   02 07 01 00 27 ba 08 00 2b 0d 44 a7 08 00 45 00

             ...
Standards For Encapsulation

d TCP/IP protocols define encapsulation for each possible type
  of network hardware
       – ...
Encapsulation Over Serial Networks

d Serial hardware transfers stream of octets
       –      Leased serial data line
   ...
Encapsulation For Avian Carriers (RFC 1149)

d Characteristics of avian carrier
   –   Low throughput
   –   High delay
  ...
A Potential Problem

d A datagram can contain up to 65535 total octets (including
  header)
d Network hardware limits maxi...
Possible Ways To Accommodate
                    Networks With Differing MTUs

d Force datagram to be less than smallest p...
Accommodating Large Datagrams

d Cannot send large datagram in single frame
d Solution
       –      Divide datagram into ...
Illustration Of When Fragmentation Needed

                              Host                                Host
        ...
Datagram Fragmentation

d Performed by routers
d Divides datagram into several, smaller datagrams called
  fragments
d Fra...
Illustration Of Fragmentation
                                                        Original datagram
                  ...
Fragmenting A Fragment

d Fragment can be further fragmented
d Occurs when fragment reaches an even-smaller MTU
d Discussi...
Reassembly

d Ultimate destination puts fragments back together
       –      Key concept!
       –      Needed in a conne...
Time To Live

d TTL field of datagram header decremented at each hop (i.e.,
  each router)
d If TTL reaches zero, datagram ...
Checksum Field In Datagram Header

d 16-bit 1’s complement checksum
d Over IP header only!
d Recomputed at each hop




In...
IP Options

d Seldom used
d Primarily for debugging
d Only some options copied into fragments
d Are variable length
d Note...
Option Code Octet
                  0           1           2    3        4         5         6   7

                COPY ...
IP Semantics

d IP uses best-effort delivery
       –      Makes an attempt to deliver
       –      Does not guarantee de...
Output From
                                          PING Program
                      PING venera.isi.edu (128.9.0.32):...
Summary

d Internet Protocol provides basic connectionless delivery
  service for the Internet
d IP defines IP datagram to ...
Summary
                                              (continued)

d Fragmentation
       –      Needed when datagram larg...
Questions?
PART VII

                   INTERNET PROTOCOL:
                FORWARDING IP DATAGRAMS




Internetworking With TCP/IP vo...
Datagram Transmission

d Host delivers datagrams to directly connected machines
d Host sends datagrams that cannot be deli...
Question



                 Does a host need to make forwarding choices?




Internetworking With TCP/IP vol 1 -- Part 7 ...
Question



                 Does a host need to make forwarding choices?

                                              A...
Example Host That Must Choose
                    How To Forward Datagrams


                                     path to ...
Two Broad Cases

d Direct delivery
       –      Ultimate destination can be reached over one network
       –      The ‘‘...
Important Design Decision


Transmission of an IP datagram between two machines on a
single physical network does not invo...
Testing Whether A Destination
               Lies On The Same Physical Network
                          As The Sender


B...
Datagram Forwarding

d General paradigm
       –      Source host sends to first router
       –      Each router passes da...
General Concept


Routers in a TCP/IP Internet form a cooperative,
interconnected structure. Datagrams pass from router to...
Efficient Forwarding

d Decisions based on table lookup
d Routing tables keep only network portion of addresses (size
  pro...
Important Idea

d Table used to decide how to send datagram known as
  routing table (also called a forwarding table)
d Ro...
Terminology

d Originally
       –      Routing used to refer to passing datagram from router to
              router
d Mo...
Conceptual Contents Of Routing Table
                 Found In An IP Router

                                        20.0....
Special Cases

d Default route
d Host-specific route




Internetworking With TCP/IP vol 1 -- Part 7         14        2005
Default Route

d Special entry in IP routing table
d Matches ‘‘any’’ destination address
d Only one default permitted
d On...
Host-Specific Route

d Entry in routing table
d Matches entire 32-bit value
d Can be used to send traffic for a specific host...
Level Of Forwarding Algorithm
                            EXAMINATION OR                    DATAGRAM
                     ...
Summary

d IP uses routing table to forward datagrams
d Routing table
       –      Stores pairs of network prefix and next...
Questions?
PART VIII

                            ERROR AND CONTROL
                                MESSAGES
                        ...
Errors In Packet Switching Networks

d Causes include
       –      Temporary or permanent disconnection
       –      Har...
Error Detection And
                                Reporting Mechanisms

d IP header checksum to detect transmission erro...
Error Reporting Mechanism

d Named Internet Control Message Protocol (ICMP)
d Required and integral part of IP
d Used prim...
ICMP Purpose


The Internet Control Message Protocol allows a router to send
error or control messages to the source of a ...
Error Reporting Vs. Error Correction

d ICMP does not
       –      Provide interaction between a router and the source of...
Important Restriction

d ICMP only reports problems to original source
d Discussion question: what major problem in the In...
ICMP Encapsulation

d ICMP message travels in IP datagram
d Entire ICMP message treated as data in the datagram
d Two leve...
ICMP Message Encapsulation

                                                                 ICMP MESSAGE



             ...
Example Encapsulation In Ethernet

                   02 07 01 00 27 ba 08 00 2b 0d 44 a7 08 00 45 00

                   ...
ICMP Message Format

d Multiple message types
d Each message has its own format
d Messages
       –      Begin with 1-octe...
ICMP Message Types
                         Type Field                 ICMP Message Type
                                0...
ICMP Message Types
                                              (continued)

                             Type Field     ...
Example ICMP Message
                                  (ICMP Echo Request)
           0                          8        ...
Example ICMP Message
                              (Destination Unreachable)
           0                         8       ...
Example ICMP Message
                                   (Redirect)
           0                         8                 ...
Situation Where An ICMP Redirect
                         Cannot Be Used

                                              R2...
Example ICMP Message
                                 (Time Exceeded)
           0                         8              ...
ICMP Trick

d Include datagram that caused problem in the error message
       –      Efficient (sender must determine how ...
Summary

d ICMP
       –      Required part of IP
       –      Used to report errors to original source
       –      Rep...
Questions?
PART IX

                          INTERNET PROTOCOL:
                         CLASSLESS AND SUBNET
                      ...
Recall



In the original IP addressing scheme, each physical network is
assigned a unique network address; each host on a...
An Observation

d Division into prefix and suffix means: site can assign and
  use IP addresses in unusual ways provided
   ...
Classful Addressing

d Three possible classes for networks
d Class C network limited to 254 hosts (cannot use all-1s or
  ...
Question

d How can we minimize the number of assigned network
  prefixes (especially class B) without abandoning the 32-bi...
Two Answers To The Minimization Question

d Proxy ARP
d Subnet addressing




Internetworking With TCP/IP vol 1 -- Part 9 ...
Proxy ARP

d Layer 2 solution
d Allow two physical networks to share a single IP prefix
d Arrange special system to answer ...
Illustration Of Proxy ARP
                                                        Main Network

                       H1 ...
Assessment Of Proxy ARP

d Chief advantages
       –      Transparent to hosts
       –      No change in IP routing table...
Subnet Addressing

d Not part of original TCP/IP address scheme
d Allows an organization to use a single network prefix for...
Example Of Subnet Addressing
                                                             Network 128.10.1.0

            ...
Interpretation Of Addresses

d Classful interpretation is two-level hierarchy
       –      Physical network identified by ...
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Transcript of "InternetWorking With TCP\IP"

  1. 1. Internetworking With TCP/IP Douglas Comer Computer Science Department Purdue University 250 N. University Street West Lafayette, IN 47907-2066 http://www.cs.purdue.edu/people/comer © Copyright 2005. All rights reserved. This document may not be reproduced by any means without written consent of the author.
  2. 2. PART I COURSE OVERVIEW AND INTRODUCTION Internetworking With TCP/IP vol 1 -- Part 1 1 2005
  3. 3. Topic And Scope Internetworking: an overview of concepts, terminology, and technology underlying the TCP/IP Internet protocol suite and the architecture of an internet. Internetworking With TCP/IP vol 1 -- Part 1 2 2005
  4. 4. You Will Learn d Terminology (including acronyms) d Concepts and principles – The underlying model – Encapsulation – End-to-end paradigm d Naming and addressing d Functions of protocols including ARP, IP, TCP, UDP, SMTP, FTP, DHCP, and more d Layering model Internetworking With TCP/IP vol 1 -- Part 1 3 2005
  5. 5. You Will Learn (continued) d Internet architecture and routing d Applications Internetworking With TCP/IP vol 1 -- Part 1 4 2005
  6. 6. What You Will NOT Learn d A list of vendors, hardware products, software products, services, comparisons, or prices d Alternative internetworking technologies (they have all disappeared!) Internetworking With TCP/IP vol 1 -- Part 1 5 2005
  7. 7. Schedule Of Topics d Introduction d Review of – Network hardware – Physical addressing d Internet model and concept d Internet (IP) addresses d Higher-level protocols and the layering principle d Examples of internet architecture Internetworking With TCP/IP vol 1 -- Part 1 6 2005
  8. 8. Schedule Of Topics (continued) d Routing update protocols d Application-layer protocols Internetworking With TCP/IP vol 1 -- Part 1 7 2005
  9. 9. Why Study TCP/IP? d The Internet is everywhere d Most applications are distributed Internetworking With TCP/IP vol 1 -- Part 1 8 2005
  10. 10. Remainder Of This Section d History of Internet protocols (TCP/IP) d Organizations d Documents Internetworking With TCP/IP vol 1 -- Part 1 9 2005
  11. 11. Vendor Independence d Before TCP/IP and the Internet – Only two sources of network protocols * Specific vendors such as IBM or Digital Equipment * Standards bodies such as the ITU (formerly known as CCITT) d TCP/IP – Vendor independent Internetworking With TCP/IP vol 1 -- Part 1 10 2005
  12. 12. Who Built TCP/IP? d Internet Architecture Board (IAB) d Originally known as Internet Activities Board d Evolved from Internet Research Group d Forum for exchange among researchers d About a dozen members d Reorganized in 1989 and 1993 d Merged into the Internet Society in 1992 Internetworking With TCP/IP vol 1 -- Part 1 11 2005
  13. 13. Components Of The IAB Organization d IAB (Internet Architecture Board) – Board that oversees and arbitrates – URL is http://www.iab.org/iab d IRTF (Internet Research Task Force) – Coordinates research on TCP/IP and internetworking – Virtually defunct, but may re-emerge Internetworking With TCP/IP vol 1 -- Part 1 12 2005
  14. 14. Components Of The IAB Organization (continued) d IETF (Internet Engineering Task Force) – Coordinates protocol and Internet engineering – Headed by Internet Engineering Steering Group (IESG) – Divided into N areas (N is 10 plus or minus a few) – Each area has a manager – Composed of working groups (volunteers) – URL is http://www.ietf.org Internetworking With TCP/IP vol 1 -- Part 1 13 2005
  15. 15. ICANN d Internet Corporation for Assigned Names and Numbers http://www.icann.org d Formed in 1998 to subsume IANA contract d Not-for-profit managed by international board d Now sets policies for addresses and domain names d Support organizations – Address allocation (ASO) – Domain Names (DNSO) – Protocol parameter assignments (PSO) Internetworking With TCP/IP vol 1 -- Part 1 14 2005
  16. 16. ICANN d Internet Corporation for Assigned Names and Numbers http://www.icann.org d Formed in 1998 to subsume IANA contract d Not-for-profit managed by international board d Now sets policies for addresses and domain names d Support organizations – Address allocation (ASO) – Domain Names (DNSO) – Protocol parameter assignments (PSO) d For fun see http://www.icannwatch.org Internetworking With TCP/IP vol 1 -- Part 1 14 2005
  17. 17. World Wide Web Consortium d Organization to develop common protocols for World Wide Web d Open membership d Funded by commercial members d URL is http://w3c.org Internetworking With TCP/IP vol 1 -- Part 1 15 2005
  18. 18. Internet Society d Organization that promotes the use of the Internet d Formed in 1992 d Not-for-profit d Governed by a board of trustees d Members worldwide d URL is http://www.isoc.org Internetworking With TCP/IP vol 1 -- Part 1 16 2005
  19. 19. Protocol Specifications And Documents d Protocols documented in series of reports d Documents known as Request For Comments (RFCs) Internetworking With TCP/IP vol 1 -- Part 1 17 2005
  20. 20. RFCs d Series of reports that include – TCP/IP protocols – The Internet – Related technologies d Edited, but not peer-reviewed like scientific journals d Contain: – Proposals – Surveys and measurements – Protocol standards Internetworking With TCP/IP vol 1 -- Part 1 18 2005
  21. 21. RFCs d Series of reports that include – TCP/IP protocols – The Internet – Related technologies d Checked and edited by IESG d Contain: – Proposals – Surveys and measurements – Protocol Standards – Jokes! Internetworking With TCP/IP vol 1 -- Part 1 19 2005
  22. 22. RFCs (continued) d Numbered in chronological order d Revised document reissued under new number d Numbers ending in 99 reserved for summary of previous 100 RFCs d Index and all RFCs available on-line Internetworking With TCP/IP vol 1 -- Part 1 20 2005
  23. 23. Requirements RFCs d Host Requirements Documents – Major revision/clarification of most TCP/IP protocols – RFC 1122 (Communication Layers) – RFC 1123 (Application & Support) – RFC 1127 (Perspective on 1122-3) d Router Requirements – Major specification of protocols used in IP gateways (routers) – RFC 1812 (updated by RFC 2644) Internetworking With TCP/IP vol 1 -- Part 1 21 2005
  24. 24. Special Subsets Of RFCs d For Your Information (FYI) – Provide general information – Intended for beginners d Best Current Practices (BCP) – Engineering hints – Reviewed and approved by IESG Internetworking With TCP/IP vol 1 -- Part 1 22 2005
  25. 25. A Note About RFCs d RFCs span two extremes – Protocol standards – Jokes d Question: how does one know which are standards? Internetworking With TCP/IP vol 1 -- Part 1 23 2005
  26. 26. TCP/IP Standards (STD) d Set by vote of IETF d Documented in subset of RFCs d Found in Internet Official Protocol Standards RFC and on IETF web site – Issued periodically – Current version is RFC 3600 Internetworking With TCP/IP vol 1 -- Part 1 24 2005
  27. 27. Internet Drafts d Preliminary RFC documents d Often used by IETF working groups d Available on-line from several repositories d Either become RFCs within six months or disappear Internetworking With TCP/IP vol 1 -- Part 1 25 2005
  28. 28. Obtaining RFCs And Internet Drafts d Available via – Email – FTP – World Wide Web http://www.ietf.org/ d IETF report contains summary of weekly activity http://www.isoc.org/ietfreport/ Internetworking With TCP/IP vol 1 -- Part 1 26 2005
  29. 29. Summary d TCP/IP is vendor-independent d Standards set by IETF d Protocol standards found in document series known as Request For Comments (RFCs) d Standards found in subset of RFCs labeled STD Internetworking With TCP/IP vol 1 -- Part 1 27 2005
  30. 30. Questions?
  31. 31. PART II REVIEW OF NETWORK HARDWARE AND PHYSICAL ADDRESSING Internetworking With TCP/IP vol 1 -- Part 2 1 2005
  32. 32. The TCP/IP Concept d Use existing network hardware d Interconnect networks d Add abstractions to hide heterogeneity Internetworking With TCP/IP vol 1 -- Part 2 2 2005
  33. 33. The Challenge d Accommodate all possible network hardware d Question: what kinds of hardware exist? Internetworking With TCP/IP vol 1 -- Part 2 3 2005
  34. 34. Network Hardware Review d We will – Review basic network concepts – Examine example physical network technologies – Introduce physical (hardware) addressing Internetworking With TCP/IP vol 1 -- Part 2 4 2005
  35. 35. Two Basic Categories Of Network Hardware d Connection oriented d Connectionless Internetworking With TCP/IP vol 1 -- Part 2 5 2005
  36. 36. Connection Oriented (Circuit Switched Technology) d Paradigm – Form a ‘‘connection’’ through the network – Send / receive data over the connection – Terminate the connection d Can guarantee bandwidth d Proponents argue that it works well with real-time applications d Example: ATM network Internetworking With TCP/IP vol 1 -- Part 2 6 2005
  37. 37. Connectionless (Packet Switched Technology) d Paradigm – Form ‘‘packet’’ of data – Pass to network d Each packet travels independently d Packet includes identification of the destination d Each packet can be a different size d The maximum packet size is fixed (some technologies limit packet sizes to 1,500 octets or less) Internetworking With TCP/IP vol 1 -- Part 2 7 2005
  38. 38. Broad Characterizations Of Packet Switching Networks d Local Area Network (LAN) d Wide Area Network (WAN) d Categories are informal and qualitative Internetworking With TCP/IP vol 1 -- Part 2 8 2005
  39. 39. Local Area Networks d Engineered for – Low cost – High capacity d Direct connection among computers d Limited distance Internetworking With TCP/IP vol 1 -- Part 2 9 2005
  40. 40. Wide Area Networks (Long Haul Networks) d Engineered for – Long distances – Indirect interconnection via special-purpose hardware d Higher cost d Lower capacity (usually) Internetworking With TCP/IP vol 1 -- Part 2 10 2005
  41. 41. Examples Of Packet Switched Networks d Wide Area Nets – ARPANET, NSFNET, ANSNET – Common carrier services d Leased line services – Point-to-point connections d Local Area Nets – Ethernet – Wi-Fi Internetworking With TCP/IP vol 1 -- Part 2 11 2005
  42. 42. ARPANET (1969-1989) d Original backbone of Internet d Wide area network around which TCP/IP was developed d Funding from Advanced Research Project Agency d Initial speed 50 Kbps Internetworking With TCP/IP vol 1 -- Part 2 12 2005
  43. 43. NSFNET (1987-1992) d Funded by National Science Foundation d Motivation: Internet backbone to connect all scientists and engineers d Introduced Internet hierarchy – Wide area backbone spanning geographic U.S. – Many mid-level (regional) networks that attach to backbone – Campus networks at lowest level d Initial speed 1.544 Mbps Internetworking With TCP/IP vol 1 -- Part 2 13 2005
  44. 44. ANSNET (1992-1995) End-User Site MCI Point of Presence d Backbone of Internet before commercial ISPs d Typical topology Internetworking With TCP/IP vol 1 -- Part 2 14 2005
  45. 45. Wide Area Networks Available From Common Carriers d Point-to-point digital circuits – T-series (e.g., T1 = 1.5 Mbps, T3 = 45 Mbps) – OC-series (e.g., OC-3 = 155 Mbps, OC-48 = 2.4 Gbps) d Packet switching services also available – Examples: ISDN, SMDS, Frame Relay, ATM Internetworking With TCP/IP vol 1 -- Part 2 15 2005
  46. 46. Example Local Area Network: Ethernet d Extremely popular d Can run over – Copper (twisted pair) – Optical fiber d Three generations – 10Base-T operates at 10 Mbps – 100Base-T (fast Ethernet) operates at 100 Mbps – 1000Base-T (gigabit Ethernet) operates at 1 Gbps d IEEE standard is 802.3 Internetworking With TCP/IP vol 1 -- Part 2 16 2005
  47. 47. Ethernet Frame Format Destination Source Frame Preamble Address Address Type Frame Data CRC 8 octets 6 octets 6 octets 2 octets 46–1500 octets 4 octets d Header format fixed (Destination, Source, Type fields) d Frame data size can vary from packet to packet – Maximum 1500 octets – Minimum 46 octets d Preamble and CRC removed by framer hardware before frame stored in computer’s memory Internetworking With TCP/IP vol 1 -- Part 2 17 2005
  48. 48. Example Ethernet Frame In Memory 02 07 01 00 27 ba 08 00 2b 0d 44 a7 08 00 45 00 00 54 82 68 00 00 f f 01 35 21 80 0a 02 03 80 0a 02 08 08 00 73 0b d4 6d 00 00 04 3b 8c 28 28 20 0d 00 08 09 0a 0b 0c 0d 0e 0 f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1 f 20 21 22 23 24 25 26 27 28 29 2a 2b 2c 2d 2e 2 f 30 31 32 33 34 35 36 37 d Octets shown in hexadecimal d Destination is 02.07.01.00.27.ba d Source is 08.00.2b.0d.44.a7 d Frame type is 08.00 (IP) Internetworking With TCP/IP vol 1 -- Part 2 18 2005
  49. 49. Point-to-Point Network d Any direct connection between two computers – Leased line – Connection between two routers – Dialup connection d Link-level protocol required for framing d TCP/IP views as an independent network Note: some pundits argue the terminology is incorrect because a connection limited to two endpoints is not technically a ‘‘network’’ Internetworking With TCP/IP vol 1 -- Part 2 19 2005
  50. 50. Hardware Address d Unique number assigned to each machine on a network d Used to identify destination for a packet Internetworking With TCP/IP vol 1 -- Part 2 20 2005
  51. 51. Hardware Address Terminology d Known as – MAC (Media Access Control) address – Physical address – Hardware unicast address d Hardware engineers assign fine distinctions to the above terms d We will treat all terms equally Internetworking With TCP/IP vol 1 -- Part 2 21 2005
  52. 52. Use Of Hardware Address d Sender supplies – Destination’s address – Source address (in most technologies) d Network hardware – Uses destination address to forward packet – Delivers packet to proper machine. d Important note: each technology defines its own addressing scheme Internetworking With TCP/IP vol 1 -- Part 2 22 2005
  53. 53. Three Types Of Hardware Addressing Schemes d Static – Address assigned by hardware vendor d Configurable – Address assigned by customer d Dynamic – Address assigned by software at startup Internetworking With TCP/IP vol 1 -- Part 2 23 2005
  54. 54. Examples Of Hardware Address Types d Configurable: proNET-10 (Proteon) – 8-bit address per interface card – All 1s address reserved for broadcast – Address assigned by customer when device installed d Dynamic MAC addressing: LocalTalk (Apple) – Randomized bidding – Handled by protocols in software Internetworking With TCP/IP vol 1 -- Part 2 24 2005
  55. 55. Examples Of Hardware Address Types (continued) d Static MAC addressing: Ethernet – 48-bit address – Unicast address assigned when device manufactured – All 1s address reserved for broadcast – One-half address space reserved for multicast (restricted form of broadcast) d Ethernet’s static addressing is now most common form Internetworking With TCP/IP vol 1 -- Part 2 25 2005
  56. 56. Bridge d Hardware device that connects multiple LANs and makes them appear to be a single LAN d Repeats all packets from one LAN to the other and vice versa d Introduces delay of 1 packet-time d Does not forward collisions or noise d Called Layer 2 Interconnect or Layer 2 forwarder d Makes multiple LANs appear to be a single, large LAN d Often embedded in other equipment (e.g., DSL modem) Internetworking With TCP/IP vol 1 -- Part 2 26 2005
  57. 57. Bridge (continued) d Watches packets to learn which computers are on which side of the bridge d Uses hardware addresses to filter Internetworking With TCP/IP vol 1 -- Part 2 27 2005
  58. 58. Layer 2 Switch d Electronic device d Computers connect directly d Applies bridging algorithm d Can separate computers onto virtual networks (VLAN switch) Internetworking With TCP/IP vol 1 -- Part 2 28 2005
  59. 59. Physical Networks As Viewed By TCP/IP d TCP/IP protocols accommodate – Local Area Network – Wide Area Network – Point-to-point link – Set of bridged LANs Internetworking With TCP/IP vol 1 -- Part 2 29 2005
  60. 60. The Motivation For Heterogeneity d Each network technology has advantages for some applications d Consequence: an internet may contain combinations of technologies Internetworking With TCP/IP vol 1 -- Part 2 30 2005
  61. 61. Heterogeneity And Addressing d Recall: each technology can define its own addressing scheme d Heterogeneous networks imply potential for heterogeneous addressing d Conclusion: cannot rely on hardware addressing Internetworking With TCP/IP vol 1 -- Part 2 31 2005
  62. 62. Summary d TCP/IP is designed to use all types of networks – Connection-oriented – Connectionless – Local Area Network (LAN) – Wide Area Network (WAN) – Point-to-point link – Set of bridged networks Internetworking With TCP/IP vol 1 -- Part 2 32 2005
  63. 63. Summary (continued) d Each technology defines an addressing scheme d TCP/IP must accommodate heterogeneous addressing schemes Internetworking With TCP/IP vol 1 -- Part 2 33 2005
  64. 64. Questions?
  65. 65. PART III INTERNETWORKING CONCEPT AND ARCHITECTURAL MODEL Internetworking With TCP/IP vol 1 -- Part 3 1 2005
  66. 66. Accommodating Heterogeneity d Approach 1 – Application gateways – Gateway forwards data from one network to another – Example: file transfer gateway d Approach 2 – Network-level gateways – Gateway forwards individual packets d Discussion question: which is better? Internetworking With TCP/IP vol 1 -- Part 3 2 2005
  67. 67. Desired Properties d Universal service d End-to-end connectivity d Transparency Internetworking With TCP/IP vol 1 -- Part 3 3 2005
  68. 68. Agreement Needed To Achieve Desired Properties d Data formats d Procedures for exchanging information d Identification – Services – Computers – Applications d Broad concepts: naming and addressing Internetworking With TCP/IP vol 1 -- Part 3 4 2005
  69. 69. The TCP/IP Internet Concept d Use available networks d Interconnect physical networks – Network of networks – Revolutionary when proposed d Devise abstractions that hide – Underlying architecture – Hardware addresses – Routes Internetworking With TCP/IP vol 1 -- Part 3 5 2005
  70. 70. Network Interconnection d Uses active system d Each network sees an additional computer attached d Device is IP router (originally called IP gateway) Internetworking With TCP/IP vol 1 -- Part 3 6 2005
  71. 71. Illustration Of Network Interconnection Net 1 R Net 2 d Network technologies can differ – LAN and WAN – Connection-oriented and connectionless Internetworking With TCP/IP vol 1 -- Part 3 7 2005
  72. 72. Building An Internet d Use multiple IP routers d Ensure that each network is reachable d Do not need router between each pair of networks Internetworking With TCP/IP vol 1 -- Part 3 8 2005
  73. 73. Example Of Multiple Networks Net 1 R2 Net 2 R2 Net 3 d Networks can be heterogeneous d No direct connection from network 1 to network 3 Internetworking With TCP/IP vol 1 -- Part 3 9 2005
  74. 74. Physical Connectivity In a TCP/IP internet, special computers called IP routers or IP gateways provide interconnections among physical networks. Internetworking With TCP/IP vol 1 -- Part 3 10 2005
  75. 75. Packet Transmission Paradigm d Source computer – Generates a packet – Sends across one network to a router d Intermediate router – Forwards packet to ‘‘next’’ router d Final router – Delivers packet to destination Internetworking With TCP/IP vol 1 -- Part 3 11 2005
  76. 76. An Important Point About Forwarding Routers use the destination network, not the destination computer, when forwarding packets. Internetworking With TCP/IP vol 1 -- Part 3 12 2005
  77. 77. Equal Treatment The TCP/IP internet protocols treat all networks equally. A Local Area Network such as an Ethernet, a Wide Area Network used as a backbone, or a point-to-point link between two computers each count as one network. Internetworking With TCP/IP vol 1 -- Part 3 13 2005
  78. 78. User’s View Of Internet d Single large (global) network d User’s computers all attach directly d No other structure visible Internetworking With TCP/IP vol 1 -- Part 3 14 2005
  79. 79. Illustration Of User’s View Of A TCP/IP Internet user’s view Internetworking With TCP/IP vol 1 -- Part 3 15 2005
  80. 80. Actual Internet Architecture d Multiple physical networks interconnected d Each host attaches to one network d Single virtual network achieved through software that implements abstractions Internetworking With TCP/IP vol 1 -- Part 3 16 2005
  81. 81. The Two Views Of A TCP/IP Internet user’s view actual connections Internetworking With TCP/IP vol 1 -- Part 3 17 2005
  82. 82. Architectural Terminology d End-user system is called host computer – Connects to physical network – Possibly many hosts per network – Possibly more than one network connection per host d Dedicated systems called IP gateways or IP routers interconnect networks – Router connects two or more networks Internetworking With TCP/IP vol 1 -- Part 3 18 2005
  83. 83. Many Unanswered Questions d Addressing model and relationship to hardware addresses d Format of packet as it travels through Internet d How a host handles concurrent communication with several other hosts Internetworking With TCP/IP vol 1 -- Part 3 19 2005
  84. 84. Summary d Internet is set of interconnected (possibly heterogeneous) networks d Routers provide interconnection d End-user systems are called host computers d Internetworking introduces abstractions that hide details of underlying networks Internetworking With TCP/IP vol 1 -- Part 3 20 2005
  85. 85. Questions?
  86. 86. PART IV CLASSFUL INTERNET ADDRESSES Internetworking With TCP/IP vol 1 -- Part 4 1 2005
  87. 87. Definitions d Name – Identifies what an entity is – Often textual (e.g., ASCII) d Address – Identifies where an entity is located – Often binary and usually compact – Sometimes called locator d Route – Identifies how to get to the object – May be distributed Internetworking With TCP/IP vol 1 -- Part 4 2 2005
  88. 88. Internet Protocol Address (IP Address) d Analogous to hardware address d Unique value assigned as unicast address to each host on Internet d Used by Internet applications Internetworking With TCP/IP vol 1 -- Part 4 3 2005
  89. 89. IP Address Details d 32-bit binary value d Unique value assigned to each host in Internet d Values chosen to make routing efficient Internetworking With TCP/IP vol 1 -- Part 4 4 2005
  90. 90. IP Address Division d Address divided into two parts – Prefix (network ID) identifies network to which host attaches – Suffix (host ID) identifies host on that network Internetworking With TCP/IP vol 1 -- Part 4 5 2005
  91. 91. Classful Addressing d Original IP scheme d Explains many design decisions d New schemes are backward compatible Internetworking With TCP/IP vol 1 -- Part 4 6 2005
  92. 92. Desirable Properties Of An Internet Addressing Scheme d Compact (as small as possible) d Universal (big enough) d Works with all network hardware d Supports efficient decision making – Test whether a destination can be reached directly – Decide which router to use for indirect delivery – Choose next router along a path to the destination Internetworking With TCP/IP vol 1 -- Part 4 7 2005
  93. 93. Division Of Internet Address Into Prefix And Suffix d How should division be made? – Large prefix, small suffix means many possible networks, but each is limited in size – Large suffix, small prefix means each network can be large, but there can only be a few networks d Original Internet address scheme designed to accommodate both possibilities – Known as classful addressing Internetworking With TCP/IP vol 1 -- Part 4 8 2005
  94. 94. Original IPv4 Address Classes 0 1 8 16 24 31 Class A 0 netid hostid Class B 1 0 netid hostid Class C 1 1 0 netid hostid Three Principle Classes 0 1 2 3 31 Class D 1 1 1 0 IP multicast Class E 1 1 1 1 0 reserved Other (seldom used) Classes Internetworking With TCP/IP vol 1 -- Part 4 9 2005
  95. 95. Important Property d Classful addresses are self-identifying d Consequences – Can determine boundary between prefix and suffix from the address itself – No additional state needed to store boundary information – Both hosts and routers benefit Internetworking With TCP/IP vol 1 -- Part 4 10 2005
  96. 96. Endpoint Identification Because IP addresses encode both a network and a host on that network, they do not specify an individual computer, but a connection to a network. Internetworking With TCP/IP vol 1 -- Part 4 11 2005
  97. 97. IP Address Conventions d When used to refer to a network – Host field contains all 0 bits d Broadcast on the local wire – Network and host fields both contain all 1 bits d Directed broadcast: broadcast on specific (possibly remote) network – Host field contains all 1 bits – Nonstandard form: host field contains all 0 bits Internetworking With TCP/IP vol 1 -- Part 4 12 2005
  98. 98. Assignment Of IP Addresses d All hosts on same network assigned same address prefix – Prefixes assigned by central authority – Obtained from ISP d Each host on a network has a unique suffix – Assigned locally – Local administrator must ensure uniqueness Internetworking With TCP/IP vol 1 -- Part 4 13 2005
  99. 99. Advantages Of Classful Addressing d Computationally efficient – First bits specify size of prefix / suffix d Allows mixtures of large and small networks Internetworking With TCP/IP vol 1 -- Part 4 14 2005
  100. 100. Directed Broadcast IP addresses can be used to specify a directed broadcast in which a packet is sent to all computers on a network; such addresses map to hardware broadcast, if available. By convention, a directed broadcast address has a valid netid and has a hostid with all bits set to 1. Internetworking With TCP/IP vol 1 -- Part 4 15 2005
  101. 101. Limited Broadcast d All 1’s d Broadcast limited to local network only (no forwarding) d Useful for bootstrapping Internetworking With TCP/IP vol 1 -- Part 4 16 2005
  102. 102. All Zeros IP Address d Can only appear as source address d Used during bootstrap before computer knows its address d Means ‘‘this’’ computer Internetworking With TCP/IP vol 1 -- Part 4 17 2005
  103. 103. Internet Multicast d IP allows Internet multicast, but no Internet-wide multicast delivery system currently in place d Class D addresses reserved for multicast d Each address corresponds to group of participating computers d IP multicast uses hardware multicast when available d More later in the course Internetworking With TCP/IP vol 1 -- Part 4 18 2005
  104. 104. Consequences Of IP Addressing d If a host computer moves from one network to another, its IP address must change d For a multi-homed host (with two or more addresses), the path taken by packets depends on the address used Internetworking With TCP/IP vol 1 -- Part 4 19 2005
  105. 105. Multi-Homed Hosts And Reliability NETWORK 1 I1 I2 I3 R A B I4 I5 NETWORK 2 d Knowing that B is multi-homed increases reliability d If interface I3 is down, host A can send to the interface I5 Internetworking With TCP/IP vol 1 -- Part 4 20 2005
  106. 106. Dotted Decimal Notation d Syntactic form for expressing 32-bit address d Used throughout the Internet and associated literature d Represents each octet in decimal separated by periods (dots) Internetworking With TCP/IP vol 1 -- Part 4 21 2005
  107. 107. Example Of Dotted Decimal Notation d A 32-bit number in binary 10000000 00001010 00000010 00000011 d The same 32-bit number expressed in dotted decimal notation 128 . 10 . 2 . 3 Internetworking With TCP/IP vol 1 -- Part 4 22 2005
  108. 108. Loopback Address d Used for testing d Refers to local computer (never sent to Internet) d Address is 127.0.0.1 Internetworking With TCP/IP vol 1 -- Part 4 23 2005
  109. 109. Classful Address Ranges Class Lowest Address Highest Address A 1.0.0.0 126.0.0.0 B 128.1.0.0 191.255.0.0 C 192.0.1.0 223.255.255.0 D 224.0.0.0 239.255.255.255 E 240.0.0.0 255.255.255.254 Internetworking With TCP/IP vol 1 -- Part 4 24 2005
  110. 110. Summary Of Address Conventions all 0s This host 1 all 0s host Host on this net 1 all 1s Limited broadcast (local net) 2 net all 1s Directed broadcast for net 2 127 anything (often 1) Loopback 3 Notes: 1 Allowed only at system startup and is never a valid destination address. 2 Never a valid source address. 3 Should never appear on a network. Internetworking With TCP/IP vol 1 -- Part 4 25 2005
  111. 111. An Example Of IP Addresses ETHERNET 128.10.0.0 WI-FI ISP NETWORK 9.0.0.0 128.210.0.0 routers Internetworking With TCP/IP vol 1 -- Part 4 26 2005
  112. 112. Example Host Addresses ETHERNET 128.10.0.0 128.10.2.3 128.10.2.8 128.10.2.26 MERLIN GUENEVERE LANCELOT (multi-homed (Ethernet (Ethernet host) host) host) 128.210.0.3 To ISP 128.10.0.6 128.10.2.70 WI-FI 128.210.50 NETWORK 128.210.0.0 TALIESYN GLATISANT (router) (router) 128.210.0.1 ARTHUR (Wi-Fi host) Internetworking With TCP/IP vol 1 -- Part 4 27 2005
  113. 113. Another Addressing Example d Assume an organization has three networks d Organization obtains three prefixes, one per network d Host address must begin with network prefix Internetworking With TCP/IP vol 1 -- Part 4 28 2005
  114. 114. Illustration Of IP Addressing Rest of the Internet Hosts and routers using other addresses Router to Internet R1 Site with three networks 128.10.0.0 R2 R3 192.5.48.0 128.211.0.0 128.211.0.9 H1 Example host Internetworking With TCP/IP vol 1 -- Part 4 29 2005
  115. 115. Summary d IP address – 32 bits long – Prefix identifies network – Suffix identifies host d Classful addressing uses first few bits of address to determine boundary between prefix and suffix Internetworking With TCP/IP vol 1 -- Part 4 30 2005
  116. 116. Summary (continued) d Special forms of addresses handle – Limited broadcast – Directed broadcast – Network identification – This host – Loopback Internetworking With TCP/IP vol 1 -- Part 4 31 2005
  117. 117. Questions?
  118. 118. PART V MAPPING INTERNET ADDRESSES TO PHYSICAL ADDRESSES (ARP) Internetworking With TCP/IP vol 1 -- Part 5 1 2005
  119. 119. Motivation d Must use hardware (physical) addresses to communicate over network d Applications only use Internet addresses Internetworking With TCP/IP vol 1 -- Part 5 2 2005
  120. 120. Example d Computers A and B on same network d Application on A generates packet for application on B d Protocol software on A must use B’s hardware address when sending a packet Internetworking With TCP/IP vol 1 -- Part 5 3 2005
  121. 121. Consequence d Protocol software needs a mechanism that maps an IP address to equivalent hardware address d Known as address resolution problem Internetworking With TCP/IP vol 1 -- Part 5 4 2005
  122. 122. Address Resolution d Performed at each step along path through Internet d Two basic algorithms – Direct mapping – Dynamic binding d Choice depends on type of hardware Internetworking With TCP/IP vol 1 -- Part 5 5 2005
  123. 123. Direct Mapping d Easy to understand d Efficient d Only works when hardware address is small d Technique: assign computer an IP address that encodes the hardware address Internetworking With TCP/IP vol 1 -- Part 5 6 2005
  124. 124. Example Of Direct Mapping d Hardware: proNet ring network d Hardware address: 8 bits d Assume IP address 192.5.48.0 (24-bit prefix) d Assign computer with hardware address K an IP address 192.5.48.K d Resolving an IP address means extracting the hardware address from low-order 8 bits Internetworking With TCP/IP vol 1 -- Part 5 7 2005
  125. 125. Dynamic Binding d Needed when hardware addresses are large (e.g., Ethernet) d Allows computer A to find computer B’s hardware address – A starts with B’s IP address – A knows B is on the local network d Technique: broadcast query and obtain response d Note: dynamic binding only used across one network at a time Internetworking With TCP/IP vol 1 -- Part 5 8 2005
  126. 126. Internet Address Resolution Protocol (ARP) d Standard for dynamic address resolution in the Internet d Requires hardware broadcast d Intended for LAN d Important idea: ARP only used to map addresses within a single physical network, never across multiple networks Internetworking With TCP/IP vol 1 -- Part 5 9 2005
  127. 127. ARP d Machine A broadcasts ARP request with B’s IP address d All machines on local net receive broadcast d Machine B replies with its physical address d Machine A adds B’s address information to its table d Machine A delivers packet directly to B Internetworking With TCP/IP vol 1 -- Part 5 10 2005
  128. 128. Illustration Of ARP Request And Reply Messages A X B Y A broadcasts request for B (across local net only) A X B Y B replies to request Internetworking With TCP/IP vol 1 -- Part 5 11 2005
  129. 129. ARP Packet Format When Used With Ethernet 0 8 16 31 ETHERNET ADDRESS TYPE (1) IP ADDRESS TYPE (0800) ETH ADDR LEN (6) IP ADDR LEN (4) OPERATION SENDER’S ETH ADDR (first 4 octets) SENDER’S ETH ADDR (last 2 octets) SENDER’S IP ADDR (first 2 octets) SENDER’S IP ADDR (last 2 octets) TARGET’S ETH ADDR (first 2 octets) TARGET’S ETH ADDR (last 4 octets) TARGET’S IP ADDR (all 4 octets) Internetworking With TCP/IP vol 1 -- Part 5 12 2005
  130. 130. Observations About Packet Format d General: can be used with – Arbitrary hardware address – Arbitrary protocol address (not just IP) d Variable length fields (depends on type of addresses) d Length fields allow parsing of packet by computer that does not understand the two address types Internetworking With TCP/IP vol 1 -- Part 5 13 2005
  131. 131. Retention Of Bindings d Cannot afford to send ARP request for each packet d Solution – Maintain a table of bindings d Effect – Use ARP one time, place results in table, and then send many packets Internetworking With TCP/IP vol 1 -- Part 5 14 2005
  132. 132. ARP Caching d ARP table is a cache d Entries time out and are removed d Avoids stale bindings d Typical timeout: 20 minutes Internetworking With TCP/IP vol 1 -- Part 5 15 2005
  133. 133. Algorithm For Processing ARP Requests d Extract sender’s pair, (IA, EA) and update local ARP table if it exists d If this is a request and the target is ‘‘me’’ – Add sender’s pair to ARP table if not present – Fill in target hardware address – Exchange sender and target entries – Set operation to reply – Send reply back to requester Internetworking With TCP/IP vol 1 -- Part 5 16 2005
  134. 134. Algorithm Features d If A ARPs B, B keeps A’s information – B will probably send a packet to A soon d If A ARPs B, other machines do not keep A’s information – Avoids clogging ARP caches needlessly Internetworking With TCP/IP vol 1 -- Part 5 17 2005
  135. 135. Conceptual Purpose Of ARP d Isolates hardware address at low level d Allows application programs to use IP addresses Internetworking With TCP/IP vol 1 -- Part 5 18 2005
  136. 136. ARP Encapsulation d ARP message travels in data portion of network frame d We say ARP message is encapsulated Internetworking With TCP/IP vol 1 -- Part 5 19 2005
  137. 137. Illustration Of ARP Encapsulation ARP MESSAGE FRAME FRAME DATA AREA HEADER Internetworking With TCP/IP vol 1 -- Part 5 20 2005
  138. 138. Ethernet Encapsulation d ARP message placed in frame data area d Data area padded with zeroes if ARP message is shorter than minimum Ethernet frame d Ethernet type 0x0806 used for ARP Internetworking With TCP/IP vol 1 -- Part 5 21 2005
  139. 139. Reverse Address Resolution Protocol d Maps Ethernet address to IP address d Same packet format as ARP d Intended for bootstrap – Computer sends its Ethernet address – RARP server responds by sending computer’s IP address d Seldom used (replaced by DHCP) Internetworking With TCP/IP vol 1 -- Part 5 22 2005
  140. 140. Summary d Computer’s IP address independent of computer’s hardware address d Applications use IP addresses d Hardware only understands hardware addresses d Must map from IP address to hardware address for transmission d Two types – Direct mapping – Dynamic mapping Internetworking With TCP/IP vol 1 -- Part 5 23 2005
  141. 141. Summary (continued) d Address Resolution Protocol (ARP) used for dynamic address mapping d Important for Ethernet d Sender broadcasts ARP request, and target sends ARP reply d ARP bindings are cached d Reverse ARP was originally used for bootstrap Internetworking With TCP/IP vol 1 -- Part 5 24 2005
  142. 142. Questions?
  143. 143. PART VI INTERNET PROTOCOL: CONNECTIONLESS DATAGRAM DELIVERY Internetworking With TCP/IP vol 1 -- Part 6 1 2005
  144. 144. Internet Protocol d One of two major protocols in TCP/IP suite d Major goals – Hide heterogeneity – Provide the illusion of a single large network – Virtualize access Internetworking With TCP/IP vol 1 -- Part 6 2 2005
  145. 145. The Concept IP allows a user to think of an internet as a single virtual network that interconnects all hosts, and through which communication is possible; its underlying architecture is both hidden and irrelevant. Internetworking With TCP/IP vol 1 -- Part 6 3 2005
  146. 146. Internet Services And Architecture Of Protocol Software APPLICATION SERVICES RELIABLE TRANSPORT SERVICE CONNECTIONLESS PACKET DELIVERY SERVICE d Design has proved especially robust Internetworking With TCP/IP vol 1 -- Part 6 4 2005
  147. 147. IP Characteristics d Provides connectionless packet delivery service d Defines three important items – Internet addressing scheme – Format of packets for the (virtual) Internet – Packet forwarding Internetworking With TCP/IP vol 1 -- Part 6 5 2005
  148. 148. Internet Packet d Analogous to physical network packet d Known as IP datagram Internetworking With TCP/IP vol 1 -- Part 6 6 2005
  149. 149. IP Datagram Layout DATAGRAM HEADER DATAGRAM DATA AREA d Header contains – Source Internet address – Destination Internet address – Datagram type field d Payload contains data being carried Internetworking With TCP/IP vol 1 -- Part 6 7 2005
  150. 150. Datagram Header Format 0 4 8 16 19 24 31 VERS HLEN TYPE OF SERVICE TOTAL LENGTH IDENT FLAGS FRAGMENT OFFSET TTL TYPE HEADER CHECKSUM SOURCE IP ADDRESS DESTINATION IP ADDRESS IP OPTIONS (MAY BE OMITTED) PADDING BEGINNING OF PAYLOAD (DATA) . . . Internetworking With TCP/IP vol 1 -- Part 6 8 2005
  151. 151. Addresses In The Header d SOURCE is the address of original source d DESTINATION is the address of ultimate destination Internetworking With TCP/IP vol 1 -- Part 6 9 2005
  152. 152. IP Versions d Version field in header defines version of datagram d Internet currently uses version 4 of IP, IPv4 d Preceding figure is the IPv4 datagram format d IPv6 discussed later in the course Internetworking With TCP/IP vol 1 -- Part 6 10 2005
  153. 153. Datagram Encapsulation d Datagram encapsulated in network frame d Network hardware treats datagram as data d Frame type field identifies contents as datagram – Set by sending computer – Tested by receiving computer Internetworking With TCP/IP vol 1 -- Part 6 11 2005
  154. 154. Datagram Encapsulation For Ethernet IP HEADER IP DATA FRAME HEADER FRAME DATA d Ethernet header contains Ethernet hardware addresses d Ethernet type field set to 0x0800 Internetworking With TCP/IP vol 1 -- Part 6 12 2005
  155. 155. Datagram Encapsulated In Ethernet Frame 02 07 01 00 27 ba 08 00 2b 0d 44 a7 08 00 45 00 00 54 82 68 00 00 f f 01 35 21 80 0a 02 03 80 0a 02 08 08 00 73 0b d4 6d 00 00 04 3b 8c 28 28 20 0d 00 08 09 0a 0b 0c 0d 0e 0 f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1 f 20 21 22 23 24 25 26 27 28 29 2a 2b 2c 2d 2e 2 f 30 31 32 33 34 35 36 37 d 20-octet IP header follows Ethernet header d IP source: 128.10.2.3 (800a0203) d IP destination: 128.10.2.8 (800a0208) d IP type: 01 (ICMP) Internetworking With TCP/IP vol 1 -- Part 6 13 2005
  156. 156. Standards For Encapsulation d TCP/IP protocols define encapsulation for each possible type of network hardware – Ethernet – Frame Relay – Others Internetworking With TCP/IP vol 1 -- Part 6 14 2005
  157. 157. Encapsulation Over Serial Networks d Serial hardware transfers stream of octets – Leased serial data line – Dialup telephone connection d Encapsulation of IP on serial network – Implemented by software – Both ends must agree d Most common standards: Point to Point Protocol (PPP) Internetworking With TCP/IP vol 1 -- Part 6 15 2005
  158. 158. Encapsulation For Avian Carriers (RFC 1149) d Characteristics of avian carrier – Low throughput – High delay – Low altitude – Point-to-point communication – Intrinsic collision avoidance d Encapsulation – Write in hexadecimal on scroll of paper – Attach to bird’s leg with duct tape d For an implementation see http://www.blug.linux.no/rfc1149
  159. 159. A Potential Problem d A datagram can contain up to 65535 total octets (including header) d Network hardware limits maximum size of frame (e.g., Ethernet limited to 1500 octets) – Known as the network Maximum Transmission Unit (MTU) d Question: how is encapsulation handled if datagram exceeds network MTU? Internetworking With TCP/IP vol 1 -- Part 6 16 2005
  160. 160. Possible Ways To Accommodate Networks With Differing MTUs d Force datagram to be less than smallest possible MTU – Inefficient – Cannot know minimum MTU d Hide the network MTU and accommodate arbitrary datagram size Internetworking With TCP/IP vol 1 -- Part 6 17 2005
  161. 161. Accommodating Large Datagrams d Cannot send large datagram in single frame d Solution – Divide datagram into pieces – Send each piece in a frame – Called datagram fragmentation Internetworking With TCP/IP vol 1 -- Part 6 18 2005
  162. 162. Illustration Of When Fragmentation Needed Host Host A B Net 1 Net 3 MTU=1500 MTU=1500 Net 2 R1 R2 MTU=620 d Hosts A and B send datagrams of up to 1500 octets d Router R1 fragments large datagrams from Host A before sending over Net 2 d Router R2 fragments large datagrams from Host B before sending over Net 2 Internetworking With TCP/IP vol 1 -- Part 6 19 2005
  163. 163. Datagram Fragmentation d Performed by routers d Divides datagram into several, smaller datagrams called fragments d Fragment uses same header format as datagram d Each fragment forwarded independently Internetworking With TCP/IP vol 1 -- Part 6 20 2005
  164. 164. Illustration Of Fragmentation Original datagram . . . . . . data1 . . data2 . . data3 Header . . . . 600 bytes . . . 600 bytes . . . 200 bytes . . Header1 data1 fragment #1 (offset of 0) Header2 data2 fragment #2 (offset of 600) Header3 data3 fragment #3 (offset of 1200) d Offset specifies where data belongs in original datagram d Offset actually stored as multiples of 8 octets d MORE FRAGMENTS bit turned off in header of fragment #3 Internetworking With TCP/IP vol 1 -- Part 6 21 2005
  165. 165. Fragmenting A Fragment d Fragment can be further fragmented d Occurs when fragment reaches an even-smaller MTU d Discussion: which fields of the datagram header are used, and what is the algorithm? Internetworking With TCP/IP vol 1 -- Part 6 22 2005
  166. 166. Reassembly d Ultimate destination puts fragments back together – Key concept! – Needed in a connectionless Internet d Known as reassembly d No need to reassemble subfragments first d Timer used to ensure all fragments arrive – Timer started when first fragment arrives – If timer expires, entire datagram discarded Internetworking With TCP/IP vol 1 -- Part 6 23 2005
  167. 167. Time To Live d TTL field of datagram header decremented at each hop (i.e., each router) d If TTL reaches zero, datagram discarded d Prevents datagrams from looping indefinitely (in case forwarding error introduces loop) d IETF recommends initial value of 255 (max) Internetworking With TCP/IP vol 1 -- Part 6 24 2005
  168. 168. Checksum Field In Datagram Header d 16-bit 1’s complement checksum d Over IP header only! d Recomputed at each hop Internetworking With TCP/IP vol 1 -- Part 6 25 2005
  169. 169. IP Options d Seldom used d Primarily for debugging d Only some options copied into fragments d Are variable length d Note: padding needed because header length measured in 32-bit multiples d Option starts with option code octet Internetworking With TCP/IP vol 1 -- Part 6 26 2005
  170. 170. Option Code Octet 0 1 2 3 4 5 6 7 COPY OPTION CLASS OPTION NUMBER Option Class Meaning 0 Datagram or network control 1 Reserved for future use 2 Debugging and measurement 3 Reserved for future use Internetworking With TCP/IP vol 1 -- Part 6 27 2005
  171. 171. IP Semantics d IP uses best-effort delivery – Makes an attempt to deliver – Does not guarantee delivery d In the Internet, routers become overrun or change routes, meaning that: – Datagrams can be lost – Datagrams can be duplicated – Datagrams can arrive out of order or scrambled d Motivation: allow IP to operate over the widest possible variety of physical networks Internetworking With TCP/IP vol 1 -- Part 6 28 2005
  172. 172. Output From PING Program PING venera.isi.edu (128.9.0.32): 64 data bytes at 1.0000 second intervals 72 bytes from 128.9.0.32: icmp_seq=0. time=170. ms 72 bytes from 128.9.0.32: icmp_seq=1. time=150. ms 72 bytes from 128.9.0.32: icmp_seq=1. time=160. ms 72 bytes from 128.9.0.32: icmp_seq=2. time=160. ms 72 bytes from 128.9.0.32: icmp_seq=3. time=160. ms ----venera.isi.edu PING Statistics---- 4 packets transmitted, 5 packets received, -25% packet loss round-trip (ms) min/avg/max = 150/160/170 d Shows actual case of duplication Internetworking With TCP/IP vol 1 -- Part 6 29 2005
  173. 173. Summary d Internet Protocol provides basic connectionless delivery service for the Internet d IP defines IP datagram to be the format of packets on the Internet d Datagram header – Has fixed fields – Specifies source, destination, and type – Allows options d Datagram encapsulated in network frame for transmission Internetworking With TCP/IP vol 1 -- Part 6 30 2005
  174. 174. Summary (continued) d Fragmentation – Needed when datagram larger than MTU – Usually performed by routers – Divides datagram into fragments d Reassembly – Performed by ultimate destination – If some fragment(s) do not arrive, datagram discarded d To accommodate all possible network hardware, IP does not require reliability (best-effort semantics) Internetworking With TCP/IP vol 1 -- Part 6 31 2005
  175. 175. Questions?
  176. 176. PART VII INTERNET PROTOCOL: FORWARDING IP DATAGRAMS Internetworking With TCP/IP vol 1 -- Part 7 1 2005
  177. 177. Datagram Transmission d Host delivers datagrams to directly connected machines d Host sends datagrams that cannot be delivered directly to router d Routers forward datagrams to other routers d Final router delivers datagram directly Internetworking With TCP/IP vol 1 -- Part 7 2 2005
  178. 178. Question Does a host need to make forwarding choices? Internetworking With TCP/IP vol 1 -- Part 7 3 2005
  179. 179. Question Does a host need to make forwarding choices? Answer: YES! Internetworking With TCP/IP vol 1 -- Part 7 3 2005
  180. 180. Example Host That Must Choose How To Forward Datagrams path to some path to other destinations destinations R1 R2 HOST d Note: host is singly homed! Internetworking With TCP/IP vol 1 -- Part 7 4 2005
  181. 181. Two Broad Cases d Direct delivery – Ultimate destination can be reached over one network – The ‘‘last hop’’ along a path – Also occurs when two communicating hosts both attach to the same physical network d Indirect delivery – Requires intermediary (router) Internetworking With TCP/IP vol 1 -- Part 7 5 2005
  182. 182. Important Design Decision Transmission of an IP datagram between two machines on a single physical network does not involve routers. The sender encapsulates the datagram in a physical frame, binds the destination IP address to a physical hardware address, and sends the resulting frame directly to the destination. Internetworking With TCP/IP vol 1 -- Part 7 6 2005
  183. 183. Testing Whether A Destination Lies On The Same Physical Network As The Sender Because the Internet addresses of all machines on a single network include a common network prefix and extracting that prefix requires only a few machine instructions, testing whether a machine can be reached directly is extremely efficient. Internetworking With TCP/IP vol 1 -- Part 7 7 2005
  184. 184. Datagram Forwarding d General paradigm – Source host sends to first router – Each router passes datagram to next router – Last router along path delivers datagram to destination host d Only works if routers cooperate Internetworking With TCP/IP vol 1 -- Part 7 8 2005
  185. 185. General Concept Routers in a TCP/IP Internet form a cooperative, interconnected structure. Datagrams pass from router to router until they reach a router that can deliver the datagram directly. Internetworking With TCP/IP vol 1 -- Part 7 9 2005
  186. 186. Efficient Forwarding d Decisions based on table lookup d Routing tables keep only network portion of addresses (size proportional to number of networks, not number of hosts) d Extremely efficient – Lookup – Route update Internetworking With TCP/IP vol 1 -- Part 7 10 2005
  187. 187. Important Idea d Table used to decide how to send datagram known as routing table (also called a forwarding table) d Routing table only stores address of next router along the path d Scheme is known as next-hop forwarding or next-hop routing Internetworking With TCP/IP vol 1 -- Part 7 11 2005
  188. 188. Terminology d Originally – Routing used to refer to passing datagram from router to router d More recently – Purists decided to use forwarding to refer to the process of looking up a route and sending a datagram d But... – Table is usually called a routing table Internetworking With TCP/IP vol 1 -- Part 7 12 2005
  189. 189. Conceptual Contents Of Routing Table Found In An IP Router 20.0.0.5 30.0.0.6 40.0.0.7 Network Network Network Network 10.0.0.0 Q 20.0.0.0 R 30.0.0.0 S 40.0.0.0 10.0.0.5 20.0.0.6 30.0.0.7 An example Internet with IP addresses TO REACH ROUTE TO NETWORK THIS ADDRESS 20.0.0.0 / 8 DELIVER DIRECT 30.0.0.0 / 8 DELIVER DIRECT 10.0.0.0 / 8 20.0.0.5 40.0.0.0 / 8 30.0.0.7 The routing table for router R Internetworking With TCP/IP vol 1 -- Part 7 13 2005
  190. 190. Special Cases d Default route d Host-specific route Internetworking With TCP/IP vol 1 -- Part 7 14 2005
  191. 191. Default Route d Special entry in IP routing table d Matches ‘‘any’’ destination address d Only one default permitted d Only selected if no other match in table Internetworking With TCP/IP vol 1 -- Part 7 15 2005
  192. 192. Host-Specific Route d Entry in routing table d Matches entire 32-bit value d Can be used to send traffic for a specific host along a specific path (i.e., can differ from the network route) d More later in the course Internetworking With TCP/IP vol 1 -- Part 7 16 2005
  193. 193. Level Of Forwarding Algorithm EXAMINATION OR DATAGRAM UPDATES OF ROUTES TO BE FORWARDED ROUTING FORWARDING TABLE ALGORITHM IP addresses used Physical addresses used DATAGRAM TO BE SENT PLUS ADDRESS OF NEXT HOP d Routing table uses IP addresses, not physical addresses Internetworking With TCP/IP vol 1 -- Part 7 17 2005
  194. 194. Summary d IP uses routing table to forward datagrams d Routing table – Stores pairs of network prefix and next hop – Can contain host-specific routes and a default route Internetworking With TCP/IP vol 1 -- Part 7 18 2005
  195. 195. Questions?
  196. 196. PART VIII ERROR AND CONTROL MESSAGES (ICMP) Internetworking With TCP/IP vol 1 -- Part 8 1 2005
  197. 197. Errors In Packet Switching Networks d Causes include – Temporary or permanent disconnection – Hardware failures – Router overrun – Routing loops d Need mechanisms to detect and correct Internetworking With TCP/IP vol 1 -- Part 8 2 2005
  198. 198. Error Detection And Reporting Mechanisms d IP header checksum to detect transmission errors d Error reporting mechanism to distinguish between events such as lost datagrams and incorrect addresses d Higher level protocols (i.e., TCP) must handle all other problems Internetworking With TCP/IP vol 1 -- Part 8 3 2005
  199. 199. Error Reporting Mechanism d Named Internet Control Message Protocol (ICMP) d Required and integral part of IP d Used primarily by routers to report delivery or routing problems to original source d Also includes informational (nonerror) functionality d Uses IP to carry control messages d No error messages sent about error messages Internetworking With TCP/IP vol 1 -- Part 8 4 2005
  200. 200. ICMP Purpose The Internet Control Message Protocol allows a router to send error or control messages to the source of a datagram, typically a host. ICMP provides communication between the Internet Protocol software on one machine and the Internet Protocol software on another. Internetworking With TCP/IP vol 1 -- Part 8 5 2005
  201. 201. Error Reporting Vs. Error Correction d ICMP does not – Provide interaction between a router and the source of trouble – Maintain state information (each packet is handled independently) d Consequence When a datagram causes an error, ICMP can only report the error condition back to the original source of the datagram; the source must relate the error to an individual application program or take other action to correct the problem. Internetworking With TCP/IP vol 1 -- Part 8 6 2005
  202. 202. Important Restriction d ICMP only reports problems to original source d Discussion question: what major problem in the Internet cannot be handled with ICMP? Internetworking With TCP/IP vol 1 -- Part 8 7 2005
  203. 203. ICMP Encapsulation d ICMP message travels in IP datagram d Entire ICMP message treated as data in the datagram d Two levels of encapsulation result Internetworking With TCP/IP vol 1 -- Part 8 8 2005
  204. 204. ICMP Message Encapsulation ICMP MESSAGE IP HEADER IP DATA FRAME HEADER FRAME DATA d ICMP message has header and data area d Complete ICMP message is treated as data in IP datagram d Complete IP datagram is treated as data in physical network frame Internetworking With TCP/IP vol 1 -- Part 8 9 2005
  205. 205. Example Encapsulation In Ethernet 02 07 01 00 27 ba 08 00 2b 0d 44 a7 08 00 45 00 00 54 82 68 00 00 f f 01 35 21 80 0a 02 03 80 0a 02 08 08 00 73 0b d4 6d 00 00 04 3b 8c 28 28 20 0d 00 08 09 0a 0b 0c 0d 0e 0 f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1 f 20 21 22 23 24 25 26 27 28 29 2a 2b 2c 2d 2e 2 f 30 31 32 33 34 35 36 37 d ICMP header follows IP header, and contains eight bytes d ICMP type field specifies echo request message (08) d ICMP sequence number is zero Internetworking With TCP/IP vol 1 -- Part 8 10 2005
  206. 206. ICMP Message Format d Multiple message types d Each message has its own format d Messages – Begin with 1-octet TYPE field that identifies which of the basic ICMP message types follows – Some messages have a 1-octet CODE field that further classifies the message d Example – TYPE specifies destination unreachable – CODE specifies whether host or network was unreachable Internetworking With TCP/IP vol 1 -- Part 8 11 2005
  207. 207. ICMP Message Types Type Field ICMP Message Type 0 Echo Reply 3 Destination Unreachable 4 Source Quench 5 Redirect (change a route) 6 Alternate Host Address 8 Echo Request 9 Router Advertisement 10 Router Solicitation 11 Time Exceeded for a Datagram 12 Parameter Problem on a Datagram 13 Timestamp Request 14 Timestamp Reply 15 Information Request 16 Information Reply 17 Address Mask Request 18 Address Mask Reply Internetworking With TCP/IP vol 1 -- Part 8 12 2005
  208. 208. ICMP Message Types (continued) Type Field ICMP Message Type 30 Traceroute 31 Datagram Conversion Error 32 Mobile Host Redirect 33 IPv6 Where-Are-You 34 IPv6 I-Am-Here 35 Mobile Registration Request 36 Mobile Registration Reply 37 Domain Name Request 38 Domain Name Reply 39 SKIP 40 Photuris Internetworking With TCP/IP vol 1 -- Part 8 13 2005
  209. 209. Example ICMP Message (ICMP Echo Request) 0 8 16 31 TYPE (8 or 0) CODE (0) CHECKSUM IDENTIFIER SEQUENCE NUMBER OPTIONAL DATA ... d Sent by ping program d Used to test reachability Internetworking With TCP/IP vol 1 -- Part 8 14 2005
  210. 210. Example ICMP Message (Destination Unreachable) 0 8 16 31 TYPE (3) CODE (0-12) CHECKSUM UNUSED (MUST BE ZERO) INTERNET HEADER + FIRST 64 BITS OF DATAGRAM ... d Used to report that datagram could not be delivered d Code specifies details Internetworking With TCP/IP vol 1 -- Part 8 15 2005
  211. 211. Example ICMP Message (Redirect) 0 8 16 31 TYPE (5) CODE (0 to 3) CHECKSUM ROUTER INTERNET ADDRESS INTERNET HEADER + FIRST 64 BITS OF DATAGRAM ... d Used to report incorrect route Internetworking With TCP/IP vol 1 -- Part 8 16 2005
  212. 212. Situation Where An ICMP Redirect Cannot Be Used R2 R3 R1 R5 S D R4 d R5 cannot redirect R1 to use shorter path Internetworking With TCP/IP vol 1 -- Part 8 17 2005
  213. 213. Example ICMP Message (Time Exceeded) 0 8 16 31 TYPE (11) CODE (0 or 1) CHECKSUM UNUSED (MUST BE ZERO) INTERNET HEADER + FIRST 64 BITS OF DATAGRAM ... d At least one fragment failed to arrive, or d TTL field in IP header reached zero Internetworking With TCP/IP vol 1 -- Part 8 18 2005
  214. 214. ICMP Trick d Include datagram that caused problem in the error message – Efficient (sender must determine how to correct problem) – Eliminates need to construct detailed message d Problem: entire datagram may be too large d Solution: send IP header plus 64 bits of data area (sufficient in most cases) Internetworking With TCP/IP vol 1 -- Part 8 19 2005
  215. 215. Summary d ICMP – Required part of IP – Used to report errors to original source – Reporting only: no interaction or error correction d Several ICMP message types, each with its own format d ICMP message begins with 1-octet TYPE field d ICMP encapsulated in IP for delivery Internetworking With TCP/IP vol 1 -- Part 8 20 2005
  216. 216. Questions?
  217. 217. PART IX INTERNET PROTOCOL: CLASSLESS AND SUBNET ADDRESS EXTENSIONS (CIDR) Internetworking With TCP/IP vol 1 -- Part 9 1 2005
  218. 218. Recall In the original IP addressing scheme, each physical network is assigned a unique network address; each host on a network has the network address as a prefix of the host’s individual address. d Routers only examine prefix (small routing tables) Internetworking With TCP/IP vol 1 -- Part 9 2 2005
  219. 219. An Observation d Division into prefix and suffix means: site can assign and use IP addresses in unusual ways provided – All hosts and routers at the site honor the site’s scheme – Other sites on the Internet can treat addresses as a network prefix and a host suffix Internetworking With TCP/IP vol 1 -- Part 9 3 2005
  220. 220. Classful Addressing d Three possible classes for networks d Class C network limited to 254 hosts (cannot use all-1s or all-0s) d Personal computers result in networks with many hosts d Class B network allows many hosts, but insufficient class B prefixes Internetworking With TCP/IP vol 1 -- Part 9 4 2005
  221. 221. Question d How can we minimize the number of assigned network prefixes (especially class B) without abandoning the 32-bit addressing scheme? Internetworking With TCP/IP vol 1 -- Part 9 5 2005
  222. 222. Two Answers To The Minimization Question d Proxy ARP d Subnet addressing Internetworking With TCP/IP vol 1 -- Part 9 6 2005
  223. 223. Proxy ARP d Layer 2 solution d Allow two physical networks to share a single IP prefix d Arrange special system to answer ARP requests and forward datagrams between networks Internetworking With TCP/IP vol 1 -- Part 9 7 2005
  224. 224. Illustration Of Proxy ARP Main Network H1 H2 H3 Router running proxy ARP R H4 H5 Hidden Network d Hosts think they are on same network d Known informally as the ARP hack Internetworking With TCP/IP vol 1 -- Part 9 8 2005
  225. 225. Assessment Of Proxy ARP d Chief advantages – Transparent to hosts – No change in IP routing tables d Chief disadvantages – Does not generalize to complex topology – Only works on networks that use ARP – Most proxy ARP systems require manual configuration Internetworking With TCP/IP vol 1 -- Part 9 9 2005
  226. 226. Subnet Addressing d Not part of original TCP/IP address scheme d Allows an organization to use a single network prefix for multiple physical networks d Subdivides the host suffix into a pair of fields for physical network and host d Interpreted only by routers and hosts at the site; treated like normal address elsewhere Internetworking With TCP/IP vol 1 -- Part 9 10 2005
  227. 227. Example Of Subnet Addressing Network 128.10.1.0 128.10.1.1 128.10.1.2 H1 H2 REST OF THE R INTERNET Network 128.10.2.0 128.10.2.1 128.10.2.2 all traffic to H3 H4 128.10.0.0 d Both physical networks share prefix 128.10 d Router R uses third octet of address to choose physical net Internetworking With TCP/IP vol 1 -- Part 9 11 2005
  228. 228. Interpretation Of Addresses d Classful interpretation is two-level hierarchy – Physical network identified by prefix – Host on the net identified by suffix d Subnetted interpretation is three-level hierarchy – Site identified by network prefix – Physical net at site identified by part of suffix – Host on the net identified by remainder of suffix Internetworking With TCP/IP vol 1 -- Part 9 12 2005
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