InternetWorking With TCP\IP

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Slide 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. Slide 2: PART I COURSE OVERVIEW AND INTRODUCTION Internetworking With TCP/IP vol 1 -- Part 1 1 2005 Slide 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 Slide 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 Slide 5: You Will Learn (continued) d Internet architecture and routing d Applications Internetworking With TCP/IP vol 1 -- Part 1 4 2005 Slide 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 Slide 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 Slide 8: Schedule Of Topics (continued) d Routing update protocols d Application-layer protocols Internetworking With TCP/IP vol 1 -- Part 1 7 2005 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 30: Questions? Slide 31: PART II REVIEW OF NETWORK HARDWARE AND PHYSICAL ADDRESSING Internetworking With TCP/IP vol 1 -- Part 2 1 2005 Slide 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 Slide 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 Slide 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 Slide 35: Two Basic Categories Of Network Hardware d Connection oriented d Connectionless Internetworking With TCP/IP vol 1 -- Part 2 5 2005 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 47: Ethernet Frame Format Preamble 8 octets Destination Address 6 octets Source Address 6 octets Frame Type 2 octets Frame Data 46–1500 octets CRC 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 64: Questions? Slide 65: PART III INTERNETWORKING CONCEPT AND ARCHITECTURAL MODEL Internetworking With TCP/IP vol 1 -- Part 3 1 2005 Slide 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 Slide 67: Desired Properties d Universal service d End-to-end connectivity d Transparency Internetworking With TCP/IP vol 1 -- Part 3 3 2005 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 79: Illustration Of User’s View Of A TCP/IP Internet user’s view Internetworking With TCP/IP vol 1 -- Part 3 15 2005 Slide 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 Slide 81: The Two Views Of A TCP/IP Internet user’s view actual connections Internetworking With TCP/IP vol 1 -- Part 3 17 2005 Slide 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 Slide 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 Slide 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 Slide 85: Questions? Slide 86: PART IV CLASSFUL INTERNET ADDRESSES Internetworking With TCP/IP vol 1 -- Part 4 1 2005 Slide 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 2 2005 Internetworking With TCP/IP vol 1 -- Part 4 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 94: Original IPv4 Address Classes 01 Class A 0 netid 8 16 24 hostid 31 Class B 1 0 netid hostid Class C 1 1 0 netid hostid Three Principle Classes 0123 Class D 1 1 1 0 31 IP multicast Class E 1 1 1 1 0 reserved Other (seldom used) Classes Internetworking With TCP/IP vol 1 -- Part 4 9 2005 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 105: Multi-Homed Hosts And Reliability NETWORK 1 I1 R A I2 B I3 I4 NETWORK 2 I5 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 Slide 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 Slide 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 Slide 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 Slide 109: Classful Address Ranges Class A B C D E Lowest Address 1.0.0.0 128.1.0.0 192.0.1.0 224.0.0.0 240.0.0.0 Highest Address 126.0.0.0 191.255.0.0 223.255.255.0 239.255.255.255 255.255.255.254 Internetworking With TCP/IP vol 1 -- Part 4 24 2005 Slide 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 Slide 111: An Example Of IP Addresses ETHERNET 128.10.0.0 WI-FI NETWORK 128.210.0.0 ISP 9.0.0.0 routers Internetworking With TCP/IP vol 1 -- Part 4 26 2005 Slide 112: Example Host Addresses ETHERNET 128.10.0.0 128.10.2.3 MERLIN (multi-homed host) 128.10.2.8 GUENEVERE (Ethernet host) 128.10.2.26 LANCELOT (Ethernet host) 128.210.0.3 To ISP 128.10.0.6 128.210.50 TALIESYN (router) 128.210.0.1 ARTHUR (Wi-Fi host) WI-FI NETWORK 128.210.0.0 128.10.2.70 GLATISANT (router) Internetworking With TCP/IP vol 1 -- Part 4 27 2005 Slide 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 Slide 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 Slide 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 Slide 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 Slide 117: Questions? Slide 118: PART V MAPPING INTERNET ADDRESSES TO PHYSICAL ADDRESSES (ARP) Internetworking With TCP/IP vol 1 -- Part 5 1 2005 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 129: ARP Packet Format When Used With Ethernet 0 8 ETHERNET ADDRESS TYPE (1) ETH ADDR LEN (6) IP ADDR LEN (4) 16 IP ADDRESS TYPE (0800) OPERATION 31 SENDER’S ETH ADDR (first 4 octets) SENDER’S ETH ADDR (last 2 octets) SENDER’S IP ADDR (last 2 octets) SENDER’S IP ADDR (first 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 137: Illustration Of ARP Encapsulation ARP MESSAGE FRAME HEADER FRAME DATA AREA Internetworking With TCP/IP vol 1 -- Part 5 20 2005 Slide 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 Slide 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 Slide 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 Slide 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 Slide 142: Questions? Slide 143: PART VI INTERNET PROTOCOL: CONNECTIONLESS DATAGRAM DELIVERY Internetworking With TCP/IP vol 1 -- Part 6 1 2005 Slide 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 Slide 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 Slide 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 Slide 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 Slide 148: Internet Packet d Analogous to physical network packet d Known as IP datagram Internetworking With TCP/IP vol 1 -- Part 6 6 2005 Slide 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 Slide 150: Datagram Header Format 0 VERS 4 HLEN 8 TYPE OF SERVICE IDENT TTL TYPE SOURCE IP ADDRESS DESTINATION IP ADDRESS IP OPTIONS (MAY BE OMITTED) BEGINNING OF PAYLOAD (DATA) . . . PADDING FLAGS 16 19 24 TOTAL LENGTH FRAGMENT OFFSET HEADER CHECKSUM 31 Internetworking With TCP/IP vol 1 -- Part 6 8 2005