Podobne
- Strona startowa
- iraq book of iraq dodipp intelligence for military personnel
- (business ebook) Internet Marketing Tips for Newbie
- Etiquette in Society, in Business, in Politics and at Home
- www mediweb pl data print php id=697
- Linux Installation and Getting Started
- Linux Installation and Getting Started (2)
- Faulkner William Azyl (SCAN dal 926)
- [3 2]Erikson Steven Wspomnien Jasnowidz
- Imperializm jako najwyzsze stadium kapitalizmu Lenin
- Tolkien J.R.R Hobbit
- zanotowane.pl
- doc.pisz.pl
- pdf.pisz.pl
- mrowkodzik.xlx.pl
Cytat
Do celu tam się wysiada. Lec Stanisław Jerzy (pierw. de Tusch-Letz, 1909-1966)
A bogowie grają w kości i nie pytają wcale czy chcesz przyłączyć się do gry (. . . ) Bogowie kpią sobie z twojego poukładanego życia (. . . ) nie przejmują się zbytnio ani naszymi planami na przyszłość ani oczekiwaniami. Gdzieś we wszechświecie rzucają kości i przypadkiem wypada twoja kolej. I odtąd zwyciężyć lub przegrać - to tylko kwestia szczęścia. Borys Pasternak
Idąc po kurzych jajach nie podskakuj. Przysłowie szkockie
I Herkules nie poradzi przeciwko wielu.
Dialog półinteligentów równa się monologowi ćwierćinteligenta. Stanisław Jerzy Lec (pierw. de Tusch - Letz, 1909-1966)
[ Pobierz całość w formacie PDF ]
.67.38.1)9.67.38.1 is an IP address (class A) having9 as the67.38.1 as theSubnets are an extension to this by considering a part of theto be a subnetwork address.IP addresses are then interpreted as.We may, for example, want to choose the bits from 8 to 25 of a class A IPaddress to indicate the subnet addresses, and the bits from 26 to 31 toindicate the actual host addresses.Figure 20 shows the subnetted addressthat has thus been derived from the original class A address.Data Communication 83 Figure 20.Class A Address with Subnet Mask and Subnet AddressWe usually use a bit mask, known as the subnet mask, to identify which bitsof the original host address field to indicate the subnet number.In the aboveexample, the subnet mask is 255.255.255.192 in decimal notation (or11111111 11111111 11111111 11000000 in bit notation).Note that, byconvention, the is masked as well.For each of these subnet values, only (2**18)-2 addresses (from 1 to 262143)are valid because of the all bits 0 and all bits 1 number restrictions.This splitwill therefore give 262142 subnets, each with a maximum of (2**6)-2 or 62hosts.The value applied to the subnet number takes the value of the full byte, withnonsignificant bits set to zero.For example, the hexadecimal value 01 in thissubnet mask assumes an 8-bit value, 01000000, and gives a subnet value of64 (and not 1 as it might seem).Applying this mask to our sample class A address 9.67.38.1 would break theaddress down as follows:00001001 01000011 00100110 00000001 = 9.67.38.1 (class A address)11111111 11111111 11111111 11------ 255.255.255.192 (subnet mask)===================================== logical_AND00001001 01000011 00100110 00------ = 9.67.38 (subnet base address)and leaves a host address of:-------- -------- -------- --000001 = 1 (host address)IP recognizes all host addresses as being on the local network for which thelogical_AND operation described above produces the same result.This isimportant for routing IP datagrams in subnet environments (see IP Routing on page 86).84 Getting Started with Data Warehouse and Business Intelligence The actual number would be:-------- 01000011 00100110 00------ = 68760 (subnet number)The subnet number shown above is a relative number, that is, it is the68760th subnet of network 9 with the given subnet mask.This number bearsno resemblance to the actual IP address that this host has been assigned(9.67.38.1) and has no meaning in terms of IP routing.The division of the original part into andparts can be chosen freely by the local administrator; except that the valuesof all zeros and all ones in the field are reserved for specialaddresses.4.1.1.4 IP DatagramThe unit of transfer of a data packet in TCP/IP is called an IP datagram.It is made up of a header containing information for IP and data that is onlyrelevant to the higher-level protocols.IP can handle fragmentation andreassembly of IP datagrams.The maximum length of an IP datagram is65,535 bytes (or octets).There is also a requirement for all TCP/IP hosts tosupport IP datagrams of up to 576 bytes without fragmentation.The IP datagram header is a minimum of 20 bytes long (see Figure 21).Data Communication 85 Figure 21.Format of an IP Datagram Header4.1.1.5 IP RoutingThere are two types of IP routing: direct and indirect.For example, Figure 22shows that the host C has a direct route to hosts B and D, and an indirectroute to host A through gateway B.Direct RoutingIf the destination host is attached to a physical network to which the sourcehost is also attached, an IP datagram can be sent directly, simply byencapsulating the IP datagram in the physical network frame.This is calleddirect delivery and is referred to as direct routing.Indirect RoutingIndirect routing occurs when the destination host is not on a network directlyattached to the source host.The only way to reach the destination is throughone or more IP gateways.In TCP/IP terminology, the terms gateway androuter are used interchangeably for a system that actually performs the dutiesof a router.The address of the first of these gateways (the first hop) is calledan indirect route in the context of the IP routing algorithm.The address of thefirst gateway is the only information needed by the source host.86 Getting Started with Data Warehouse and Business Intelligence Figure 22.Direct and Indirect RoutingIP Routing TableThe determination of available direct routes is derived from the list of localinterfaces available to IP and is composed by IP automatically at initialization.A list of networks and associated gateways (indirect routes) must beconfigured to be used with IP routing if required.Each host keeps the set of mappings between the:" Destination IP network addresses" Routes to next gatewaysThe mappings are stored in the IP routing table (see Figure 23).Three typesof mappings can be found in this table:" Direct routes, for locally attached networks" Indirect routes, for networks reachable through one or more gateways" Default route, which contains the (direct or indirect) route to be used if thedestination IP network is not found in the mappings of type 1 and 2 above.Data Communication 87 Figure 23.Routing Table ScenarioThe routing table of host F might contain the symbolic entries shown in theFigure 24.destination router interface129.7.0 F lan0128.15.0 E lan0128.10.0 E lan0default B lan0127.1 loopback loFigure 24.IP Routing Table Entries ExampleIP Routing AlgorithmIP uses a unique algorithm to route an IP datagram.Figure 25 shows an IProuting algorithm with subnets.88 Getting Started with Data Warehouse and Business Intelligence Figure 25.IP Routing Algorithm (with Subnets)Notes:" IP routing is an iterative process.It is applied by every host handling adatagram, except for the host to which the datagram is finally delivered." Routing tables and the routing algorithm are local to any host in an IPnetwork.To forward IP datagrams on behalf of other hosts, routersmust exchange their routing table information with other routers in thenetwork, using special routing protocols.4.1.2 APPCThe following sections provide information about the advancedprogram-to-program communication (APPC) protocol.4.1.2.1 SNA BasisSNA is a communications architecture that was originally designed toaddress the increasing complexity of data processing and communicationsneeds as technology advanced.SNA is not a product, it is an architecturethat provides a blueprint or specification of how diverse products can connectData Communication 89 and communicate with each other.It defines a set of rules that describe thetransport of data and specify, for example, what the data looks like, how it isto be packaged and who the sender and receiver are.SNA LayersSNA is a structured architecture that consists of seven well-defined layers,each of which performs a specific network function.As a result of thisstructure, SNA products have compatible interfaces that facilitateinterconnection and communication.Their new functions and technologiescan be added to the network with no disruption to the flow of data.The layersdefined in SNA are:" Transaction servicesProvides application services, such as distributed database access ordistributed file management." Presentation servicesIn general, formats the data for different media and sharing of devices." Data flow controlSynchronizes the flow of data within a network, correlates dataexchanges, and groups related data into units
[ Pobierz całość w formacie PDF ]