ARPANET. On the Way to Today's Internet. The Beginning of ARPANET ARPANET. Result: ARPANET (predecessor of today's Internet) California

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1 On the Way to Today's ARPANET Goal: Interconnection of computers and networks using uniform protocols A particularly important initiative was initiated by the ARPA (Advanced Research Project Agency, with military interests) The participation of the military was the only sensible way to implement such an ambitious and extremely expensive project The OSI specification was still in developing phase Design objective for ARPANET The operability of the network should remain intact even after a largest disaster possible, e.g. a nuclear war, thus high connectivity and connectionless transmission Network computer and host computer are separated ARPA Advanced Research Projects Agency Result: ARPANET (predecessor of today's ) Subnet ARPANET 1969 Page 1 Page 2 ARPANET The Beginning of ARPANET A node consists of an IMP a host -host Protocol XDS 940 Stanford Research Institutes (SRI) A subnet consists of: Interface Message Processors (IMPs), which are connected by leased transmission circuits High connectivity (in order to guarantee the demanded reliability) Several protocols for the communication between IMP-IMP, host-imp, -IMP Protocol Source IMP to destination IMP protocol Subnet IMP-IMP protocol IMP IBM 360/75 IMP University of California Santa Barbara (UCSB) IMP IMP XDS 1-7 IMP California University of California Los Angeles (UCLA) DEK PDP-10 University of Utah ARPANET (December 1969) Page 3 Page 4

2 UCSB Evolution by ARPANET Very fast evolution of ARPANET within shortest time: SRI UCLA Utah USC Illinois WITH Harvard UCSB UCLA SRI Utah Illinois WITH Stanford USC Harvard Aberdeen ARPANET in April 1972 ARPANET in September 1972 CMU Interworking Problem: Interworking! Simultaneously to the ARPANET further (smaller) networks were developed. All the LANs, MANs, WANs had different protocols, media, could not be interconnected at first and were not be able to communicate with each another. Therefore: Development of uniform protocols on the transport- and network level (without a too accurate definition of these levels, in particular without exact coordination with the respective OSI levels). Result: TCP/IP networks. Page 5 Page 6 TCP/IP TCP/IP and the OSI Reference Model Developed 1974: Transmission Control Protocol/ Protocol (TCP/IP) Requirements: Fault tolerance Maximal possible reliability and availability Flexibility (i.e. suitability for applications with very different requirements) The result: Network protocol IP; ( Protocol; connectionless) End-to-end protocols TCP (Transmission Control Protocol; connection-oriented) and UDP (User Datagram Protocol; connectionless) Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer ISO/OSI Application Layer Transport Layer (TCP/UDP) Layer (IP) -to-network Layer TCP/IP Page 7 Page 8

3 From the ARPANET to the 1983 TCP/IP became the official protocol of ARPANET. ARPANET was connected with many other USA networks. Intercontinental connecting with networks in Europe, Asia, Pacific. The total network evolved this way to a world-wide available network (called ) and gradually lost its early militarily dominated character. What does it mean: a computer is connected to the? - Use of the TCP/IP protocol suite - Accessibility over an IP address - Ability to send IP packets In its early period, the was limited to the following applications: No central administrated network, but a world-wide union from many individual, different networks under local control (and financing) the consisted of 3,000 networks with 200,000 computers. That was however only the beginning of a rapid evolution. Remote login File transfer electronic mail (partly because the US post was not very reliable and the different time zones made telephone accessibility of the telephone partner more difficult) running jobs on external computers exchange of data between computers Page 9 Page 10 Evolution of the Evolution of the Until 1990: the was comparatively small, only used by universities and research institutions. 1990: The WWW (World Wide Web) - first developed by the CERN for the simplification of communication within the field of high-energy physics - became, together with HTML and Netscape browsers, a from nobody foreseen killer application ; this was the breakthrough for the acceptance of the. Emergence of so-called Service Providers (ISP), i.e. companies, which make their computers available as access points to the. Millions of new (predominantly non-academic) users! New applications, e.g. E-Commerce 1995: Backbones, ten thousands LANs, millions attached computers, exponentially rising number of users 1998: The number of attached computers is doubled approx. all 6 months 1999: The transferred data volume is doubled in less than 4 months At mid of 2005: (estimated) 350 million of hosts attached to the Page 11 Page 12

Evolution in Europe and Intranet Communication via the TCP/IP protocols Local operators control and finance Global coordination by some organizations Providers provide access points for private

Computers are sealed off from the global (data security) Heterogeneous network structures from different branches can be integrated with TCP/IP easily Use of applications like in the WWW for internal

4 Evolution in Europe and Intranet Communication via the TCP/IP protocols Local operators control and finance Global coordination by some organizations Providers provide access points for private individuals Intranet Enterprise-internal communication with the same protocols and applications as in the. Computers are sealed off from the global (data security) Heterogeneous network structures from different branches can be integrated with TCP/IP easily Use of applications like in the WWW for internal data exchange Date Page 13 Page 14 The TCP/IP Protocol Suite Sandglass Model Protocols HTTP IGMP FTP Telnet SMTP DNS SNMP TFTP TCP UDP ICMP IP ARP RARP Application Layer Transport Layer Layer , File Transfer, Video Conferencing, HTTP, SMTP, FTP, Because of the small number of central protocols but the large number of applications and communication networks, the TCP/IP protocol stack (and applications/networks) can be represented like a sandglass. Networks Ethernet Token Ring Token Bus Wireless LAN -tonetwork Layer Twisted Pair, Optical Fiber, Radio, Page 15 Page 16

5 Layer IP Protocol Raw division into three tasks: Data transfer over a global network Route decision at the sub-nodes Control of the network or transmission status Routing Protocols Routing Tables Transfer Protocols: IPv4, IPv6 Control Protocols: ICMP, ARP, RARP, IGMP IP: connectionless, unreliable transmission of datagrams/packets ( Best Effort ) Transparent end-to-end communication between the hosts Routing, interoperability between different network types IP addressing (IPv4): Uses logical 32-bit addresses Hierarchical addressing 3 network classes 4 address formats (including multicast) Fragmenting and reassembling of packets Maximum packet size: 64 kbyte (in practice: 1500 byte) At present commonly used: Version 4 of IP protocol: IPv4 Page 17 Page 18 IP Packet Version IHL Time to Live Identification 32 Bits (4 Bytes) Type of Service Protocol DM F F Source Address Destination Address Options (variable, 0-40 Byte) DATA (variable) Total Length Fragment Offset Header Checksum Padding IP Header, usually 20 Bytes Header Data The IP Header (1) Version: IP version number (for simultaneous use of several IP versions) IHL: IP Header Length (in words of 32 bit; between 5 and 15, depending upon options) Type of Service: Indication of the desired service: Combination of reliability (e.g. file transfer) and speed (e.g. audio) 3 bit priority (0 = normal data, 7 = control packet) Precedence Delay Total Length: Length of the entire packet (in byte, = bytes) Identification: definite marking of a packet Time to Live (TTL): Lifetime of packets is limited to maximal 255 Hops (endless circling of packets in the network is prevented). In principle, also the processing time in routers is to be considered, which does not happen in practice. The counter is reduced with each hop, with 0 the packet is discarded. D T R unused Throughput Reliability Page 19 Page 20

6 The IP Header (2) DF: Don't Fragment. All routers must forward packets up to a size of 576 byte, everything beyond that is optional. Larger packets with set DF-bit therefore cannot take each possible way in the network. MF: More Fragments. 1 - further fragments follow. 0 - last fragment of a datagram) Fragment Offset: Sequence number of the fragments of a packet (2 13 = 8192 possible fragments). The offset states, at which place of a packet (counted in multiples of 8 byte) a fragment belongs. From this a maximum length of 8192 * 8 byte = byte results for a packet. Protocol: Which transport protocol is used in the data part (UDP, TCP, )? To which transport process the packet is to be passed on? Header Checksum: 1 s complement of the sum of the 16-bit half words of the. Must be computed with each hop (since TTL changes) Source Address/Destination address: Network and host numbers of sending and receiving computer. This information is used by routers for the routing decision. Fragmentation A too large or too small packet length prevents a good performance. Additionally there are often size restrictions (buffer, protocols with length specifications, standards, allowed access time to a channel, ) The data length must be a multiple of 8 byte. Exception: the last fragment, there only the remaining data are packed, padding to 8 byte units does not take place. If the DF -bit is set, the fragmentation is prevented. Ident. Flags Offset Data 777 x bytes IP 777 x x x Page 21 Page 22 The IP Header (3) IP Addressing Options: Prepare for future protocol extensions. Coverage: Multiple of 4 byte, therefore possibly padding is necessary. At present, 5 options are defined, however none is supported by common routers: Security: How secret is the transported information? (Application e.g. in military: Avoidance of crossing of certain countries/networks.) Strict Source Routing: Complete path defined from the source to the destination host by providing the IP addresses of all routers which are crossed. (Use by system managers e.g. in case of damaged routing tables or for time measurements) Loose Source Routing: The carried list of routers must be passed in indicated order. Additional routers are permitted. Record Route: Recording of the IP addresses of the routers passed. (Maximally 9 IP addresses possible, nowadays too few.) Time Stamp: Records router addresses (32 bits) as well as a time stamp for each router (32 bits). Application e.g. in fault management. Page 23 Unique IP address for each host and router. IP addresses are 32 bits long and are used in the Source Address as well as in Destination Address field of IP packets. The IP address is structured hierarchical and refers to a certain network, i.e. machines with connection to several networks have several IP addresses. Structure of the address: Network address for physical network (e.g ) and host address for a machine in the addressed network (e.g ) 32 bits 126 networks with 2 24 host each Class (starting from ) A 0 Network networks with 2 16 hosts each B 10 Network (starting from ) C D E 110 Network 1110 Multicast address 1111 Reserved for future use networks (LANs) with 256 hosts each (starting from ) Page 24

7 IP Addresses Destination IP Address IP Addresses and Routing 12.x.x.x x.x Connection x x.x Network Interface b a x.x direct a Router x x.x.x.x direct default b a a b Binary format Dotted Decimal Notation Each node has (at least) one world-wide unique IP address Router or gateways, which link several networks with one another, have for each network an assigned IP address Page 25 Page 26 IP Addressing - Examples Address Space The representation of the 32-bit addresses is divided into 4 sections of each 8 bits: ,25% 6,25% Class B address Special addresses: Class B address of RWTH Aachen Subnet (Computer science 4) This host Terminal Shadow 50,00% 12,50% Klasse Class A Klasse Class B Klasse Class C Klasse Class D Klasse Class E in this network Broadcast in own local area network 25,00% Network Broadcast in the remote network 127 arbitrary Loop, no sending to the network Page 27 Page 28

8 Problems IP Addresses are scarce Nobody had thought about such a strong growth of the (otherwise one would have defined longer addresses from the beginning). Too many Class A address blocks were assigned in the first years. Inefficient use of the address space. Example: if 500 devices in an enterprise are to be attached, a Class B address block is needed, but by this unnecessarily more than host addresses are blocked. Solution approach Extension of the address space within IPv6 against the actual version IPv4 IP version 6 has 128 bit for addresses 7 x IP addresses per square meter of the earth's surface (including the oceans!) one address per molecule on earth's surface! But: The success of IPv6 is not by any means safe! (The introduction of IPv6 is tremendously difficult: Interoperability, costs, migration strategies,.) Page 29 IP Subnets Problem: Class C-networks are very small, Class B-networks often already too large. Therefore exists the possibility of dividing an through the IP-address identified network into so-called subnets. Rest of the All traffic for Examples for subnets: subnet mask Router Ethernet A Ethernet A Ethernet B Ethernet B Ethernet A Ethernet A Ethernet B Ethernet B Page 30 IP Subnets Within an IP network address block, several physical networks can be addressed Some bits of the host address part are used as network ID A Subnet mask identifies the abused bits Class B address Subnet Mask Network All hosts of a network should use the same subnet mask Routers can determine through combination of an IP address and a subnet mask, into which subnet a packet must be sent Network Subnet Page 31 IP Subnets - Computation of the Destination The entrance router of the RWTH, which receives the IP packet, does not know, where host is located AND IP address Subnet mask Network of the addressed host The router computes the subnet and sends the packet to the router, which links this subnet. Page 32

9 Example of a Subnet Assigned network address for the RWTH: Info IV Subnet mask for each subnet = Other format for writing of addresses in subnets: /24 Number of bits for (sub)network address 254 hosts per subnet: s have the addresses is reserved for the subnet 255 is reserved for broadcast in the subnet More flexible Addressing Problem: static categorization of IP addresses - how to use the very small class C networks efficiently? Remedy: Classless Inter-Domain Routing (CIDR) Weakening of the rigid categorization by replacing the static classes by network prefixes of variable length Example: /17: The first 17 bits of the IP address are used for the network identification Used together with routing: Backbone router, e.g. on transatlantic links only considers the first 13 bits; thus small routing tables, little cost of routing decision Routers of an ISP considers e.g. only the first 15 bits Routers in company networks consider e.g. the first 25 bits Page 33 Page 34 NAT Network Address Translation NAT Variants Each internal computer in the Intranet needs an own IP address to communicate with the others. For this purpose, private address blocks are reserved, which everyone may use within its own networks and which are never routed in the : When using addresses of those range, the internal computers can communicate with each other But: packets with those addresses are not forwarded by a router. Thus: routers, which are attached to the external world need a global address Assign a few IP addresses to a company which are known by a NAT box which usually is installed with the router When data are leaving the own network, an address translation takes place: the NAT box exchanges the private address with a globally valid one Side effect: hiding of the internal network structure (security) Page 35 NAT is available in several variants, known under different names: Basic NAT (also: Static NAT) Each private IP address is translated into one certain external IP Either, you need as much external addresses as private ones, otherwise no retranslation is possible when a reply arrives Or, you manage a pool of external IP addresses and assign one dynamically when a request is sent out Private IP router with NAT box Map to Private IP router with NAT box Currently mapped: Page 36

NAT Variants NAPT Network Address Port Translation Disadvantages of static NAT: With static mapping, you need as much official IP addresses as you have computers With dynamic mapping, you need less

10 NAT Variants NAPT Network Address Port Translation Disadvantages of static NAT: With static mapping, you need as much official IP addresses as you have computers With dynamic mapping, you need less official IP addresses, but for times of high traffic you nevertheless need nearly as much addresses as local computers Those approaches help to hide the network structure, but not to save addresses Hiding NAT (also: NAPT: Network Address Port Translation, Masquerading) Translate several local addresses into the same external address Now: some more details are necessary to deliver a response router with NAT box destination? Private IP to: Map to Protocol TCP TCP Port (local) IP (local) Port (global) IP (global) IP (destination) Port (destination) Page 37 Page 38 Problems with NAPT The new IP - IPv6 IPv6 (December 1995, RFC 1883) NAPT works well with communication initiated from the Intranet. But: how could someone from outside give a request to the Intranet (e.g. to the webserver)? NAPT box needs to be a bit more intelligent Some static information has to be stored, e.g. each incoming request with port 80 has to be mapped to the private address of the webserver Still problems with applications like e.g. ICQ Thus, only more IP addresses really help to solve the problem Publication of the standard (January 1995, RFC 1752) Specification for IPng (December 1994, RFC 1726) First requirements for IPng (December 1993, RFC 1550). Simpler structure of the s More automatism Simpler configuration Performance improvements Migration strategies More security Larger address space IPv4 (September 1981, RFC 791) Page 39 Page 40

11 IPv6 Why changing the protocol, when IPv4 works well? Dramatically increasing need for new IP addresses Improved support of real time applications Security mechanisms (Authentication and data protection) Differentiation of types of service, in particular for real time applications Support of mobility (hosts can go on journeys without address change) Simplification of the protocol in order to ensure a faster processing Reduction of the extent of the routing tables Option for further development of the protocol Page 41 IPv6 - Characteristics Address size 128-bit addresses (8 groups of each 4 hexadecimal numbers) Improved option mechanism Simplifies and accelerates the processing of IPv6 packets in routers Auto-configuration of addresses Dynamic allocation of IPv6-addresses Improvement of the address flexibility Anycast address: Reach any one out of several Support of the reservation of resources Marking of packets for special traffic Security mechanisms Authentication and Privacy Simpler structure: IHL: redundant, no variable length of by new option mechanism Protocol, fragmentation fields: redundant, moved into the options Checksum: Already done by layer 2 and 4 Page 42 IPv6 Main Header IPv6 Extension Headers Version: IP version number Priority: 4 bits for priority. 1 - News, 4 - ftp, 6 - telnet, 8 to 15 - real time traffic Flow label: virtual connection with certain characteristics/requirements PayloadLen: packet length after the 40- byte Next Header: 8-bit selector. Indicates the type of the following extension (or the transport ) HopLimit: At each node decremented by one. At zero the packet is discarded Source Address: The address of the original sender of the packet Destination Address: The address of the receiver (not necessarily the final destination, if there is an optional routing ) Next Header/Data: if an extension is specified, it follows after the main. Otherwise, the data are following Version (4) Priority (4) PayloadLen (16) Flow label (24) Source Address (128) Destination Address (128) Next Header/Data Next Header (8) HopLimit (8) The prefix of an address characterizes geographical areas, providers, local internal areas, Page 43 Optional data follows in extension s. There are 6 s defined: Hop by Hop (information for single links) All routers have to examine this field. Momentarily only the support of Jumbograms (packets exceeding the normal IP packet length) is defined (length specification). Routing (definition of a full or partly specified route) Fragmentation (administration of fragments) Difference to IPv4: Only the source can do fragmentation. Routers for which a packet is too large, only send an error message back to the source. Authentication (of the sender) Ciphered data Destination options (additional information for the destination) Page 44

12 IPv4 vs. IPv6: Header Priority Version En IHL Type OF of Service service Identification Time to Live Protocol SOURCE Source ADDRESS Address Destination ADDRESS Address Totally Length length Fragment offset Header Checksum Options (variable)/padding Version En Flow Label label NEXT Next PayloadLen Hop Limit limit Header s SOURCE Source ADDRESS Address SOURCE Source ADDRESS Address SOURCE Source ADDRESS Address SOURCE Source ADDRESS Address Coexistence of IPv4 and IPv6 IPv6 cannot be introduced over night for some time both IP variants will be used in parallel. New network interface card drivers support both versions of IP, thus they are able to communicate with the newer version But: how to enable two modern IPv6-based hosts to communicate if only an IPv4- based network is in between? 1. Header Conversion Router translates an incoming IPv6 packet into a IPv4 packet, receiving router retranslates But: reconstruction of e.g. flow label??? DATA Data The IPv6 is longer, but this is only caused by the longer addresses. Otherwise it is better sorted and thus faster to process by routers. Destination ADDRESS Address Destination ADDRESS Address Destination ADDRESS Address Destination ADDRESS Address NEXT Next Header /DATA/ Data Page 45 payload IPv6 IPv6 network payload IPv4 mostly IPv4 Routers which speak IPv4 and IPv6 in parallel payload IPv6 IPv6 network Page 46 Coexistence of IPv4 and IPv6 Virtual Private Network (VPN) 2. Tunneling Router at the entry to the IPv4-based network encapsulate an incoming IPv6 packet into a new IPv4 packet with destination address of the next router also supporting IPv6 payload IPv6 payload IPv6 mostly IPv4 IPv4 payload IPv6 By a Virtual Private Network (VPN) a network infrastructure is understood, in which distributed components belonging to one logical private network communicate with one another over a public network (e.g. ) VPNs are used frequently for the connection of geographically distributed organizations (Intranet in the ) VPNs ensure authenticated access and permit the protection of sensitive data in distributed networks by encryption of data The logical connection between private components over a public network is achieved again by tunneling an IPv4 connection with e.g. IPsecure IPv6 network IPv6 tunnel through IPv4 IPv6 network More overhead because of two s for one packet, but no information loss due to conversion Tunneling is a general concept also used for multicast, VPN, etc: it simply means pack a whole packet as it is into a new packet of different protocol VPN Page 47 Page 48

13 Tunneling Mechanism Tunneling here: Encapsulate packets into encrypted IP packets, e.g. by using IPsecure. Packets directed to the remote network part by this remain unchanged, but are the payload of an encrypted packet. Page 49

OSI Reference Model. Application Layer. Presentation Layer. Session Layer. Transport Layer. Chapter 4: Application Protocols.

OSI Reference Model. Application Layer. Presentation Layer. Session Layer. Transport Layer. Chapter 4: Application Protocols. Chapter 3: Protocols and Services 3.1: 3 - The Internet Protocol IP 3.2: Routing in the Internet 3.3: Auxiliary Protocols 3.4: Quality of Service 3.5: 4 - Transport Protocols TCP and UDP OSI Reference