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.Designing APPN Internetworks 6-5 When to Use APPN Versus Alternative Methods of SNA TransportFigure 6-3 Sample network for which branch-to-branch routing is required.DatacenterToken TokenRing RingBackboneBranchAs you also learn in this chapter, scalability issues make it advantageous to keep the number ofnetwork nodes as small as possible.Understanding where native routing and COS is needed is keyin minimizing the number of network nodes.In summary, choosing where to implement APPN must be decided based on cost, scalability, andwhere native routing and COS are needed.Implementing APPN everywhere in your network mightseem to be an obvious solution, even when not necessary.It must be understood, however, that if youwere to deploy APPN everywhere in your network it probably would be a more costly solution thannecessary and may potentially lead to scalability problems.Consequently, the best solution is todeploy APPN only where it is truly needed in your network.When to Use APPN Versus Alternative Methods of SNA TransportAPPN and boundary network node (BNN)/boundary access node (BAN) over Frame Relay usingRFC 1490 are the two methods of native SNA transport, where SNA is not encapsulated in anotherprotocol.BAN and BNN allow direct connection to an FEP, using the Frame Relay network to switchmessages, rather than providing direct SNA routing.Although native might seem to be the appropriate strategy, APPN comes at the price of cost andnetwork scalability, as indicated in the preceding section.With BNN/BAN additional cost is requiredto provide multiprotocol networking because the FEP does not handle multiple protocols.Thisimplies that additional routers are required in the data center for other protocols and separate virtualcircuits are required to guarantee service delivery for the SNA or APPN traffic.DLSw+ provides encapsulation of SNA, where the entire APPN message is carried as data inside aTCP/IP message.There is often concern about the extra 40 bytes of header associated with TCP/IP.However, because Cisco offers alternatives such as Data Link Switching Lite, Fast SequencedTransport (FST), and Direct Transport, which have shorter headers, header length is deemednoncritical to this discussion.6-6 Cisco CCIE Fundamentals: Network Design Overview of APPNDLSw+ is attractive for those networks in which the end stations and data center will remainSNA-centric, but the backbone will be TCP/IP.This allows a single protocol across the backbone,while maintaining access to all SNA applications.DLSw+ does not provide native APPN routing,nor does it provide native COS.Consequently, DLSw+ is preferable for networks, in which cost isa key criterion, that have the following characteristics:" A single data center or mainframe" Single links from the branchesIn general, DLSw+ is a lower-cost solution that requires less memory and software.In the vastmajority of networks, DLSw+ will be combined with APPN using APPN only where routingdecisions are critical.With TCP/IP encapsulation, the TCP layer provides the same reliable deliveryas SNA/APPN, but does not provide the native routing and COS.TN3270 transports 3270 data stream inside a TCP/IP packet without SNA headers.Therefore, thissolution assumes that the end station has only a TCP/IP protocol stack and no SNA.Therefore,TN3270 is not an alternative to APPN because APPN assumes the end station has an SNA protocolstack.APPN, like DLSw+, may still be required in the network to route between TN3270 serversand multiple mainframes or data centers.In summary, APPN will frequently be used with DLSw+ in networks when a single backboneprotocol is desired.BAN/BNN provides direct connectivity to the FEP but lacks the multiprotocolcapabilities of other solutions.TN3270 is used only for TCP/IP end stations.Overview of APPNThis section provides an overview of APPN and covers the following topics:" Defining Nodes" Establishing APPN Sessions" Understanding Intermediate Session Routing" Using Dependent Logical Unit Requester/ServerDefining NodesNodes, such as ACF/VTAM, OS/400 and Communications Server/2 (CS/2), can be defined as eithernetwork nodes or end nodes.When you have a choice, consider the following issues:" Network size How large is the network? Building large APPN networks can introducescalability issues.Reducing the number of network nodes is one solution for avoiding scalabilityproblems.For more information on reducing the number of network nodes, see the section Reducing the Number of Network Nodes later in this chapter." Role of the node Is it preferable to have this node performing routing functions as well asapplication processing? A separate network node can reduce processing cycles and memoryrequirements in an application processor.Generally, you should define a network node whenever a routing decision needs to be made.Designing APPN Internetworks 6-7 Overview of APPNAPPN Node IdentifiersAn APPN node is identified by its network-qualified CP name, which has the format netid.name.Thenetwork identifier (netid) is an eight-character name that identifies the network or subnetwork inwhich the resource is located.The network identifier and name must be a combination of uppercaseletters (A through Z), digits (0 through 9), and special characters ($,#,or @) but cannot have a digitas the first character.Establishing APPN SessionsIn order for an APPN session to be established, the following must occur:1 The end user requests a session with an application, which causes the end node to begin theprocess of session establishment by sending a LOCATE message to its network node server.Forsession initiation, the network node server provides the path to the destination end node, whichallows the originating end node to send messages directly to the destination [ Pobierz całość w formacie PDF ]
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.Designing APPN Internetworks 6-5 When to Use APPN Versus Alternative Methods of SNA TransportFigure 6-3 Sample network for which branch-to-branch routing is required.DatacenterToken TokenRing RingBackboneBranchAs you also learn in this chapter, scalability issues make it advantageous to keep the number ofnetwork nodes as small as possible.Understanding where native routing and COS is needed is keyin minimizing the number of network nodes.In summary, choosing where to implement APPN must be decided based on cost, scalability, andwhere native routing and COS are needed.Implementing APPN everywhere in your network mightseem to be an obvious solution, even when not necessary.It must be understood, however, that if youwere to deploy APPN everywhere in your network it probably would be a more costly solution thannecessary and may potentially lead to scalability problems.Consequently, the best solution is todeploy APPN only where it is truly needed in your network.When to Use APPN Versus Alternative Methods of SNA TransportAPPN and boundary network node (BNN)/boundary access node (BAN) over Frame Relay usingRFC 1490 are the two methods of native SNA transport, where SNA is not encapsulated in anotherprotocol.BAN and BNN allow direct connection to an FEP, using the Frame Relay network to switchmessages, rather than providing direct SNA routing.Although native might seem to be the appropriate strategy, APPN comes at the price of cost andnetwork scalability, as indicated in the preceding section.With BNN/BAN additional cost is requiredto provide multiprotocol networking because the FEP does not handle multiple protocols.Thisimplies that additional routers are required in the data center for other protocols and separate virtualcircuits are required to guarantee service delivery for the SNA or APPN traffic.DLSw+ provides encapsulation of SNA, where the entire APPN message is carried as data inside aTCP/IP message.There is often concern about the extra 40 bytes of header associated with TCP/IP.However, because Cisco offers alternatives such as Data Link Switching Lite, Fast SequencedTransport (FST), and Direct Transport, which have shorter headers, header length is deemednoncritical to this discussion.6-6 Cisco CCIE Fundamentals: Network Design Overview of APPNDLSw+ is attractive for those networks in which the end stations and data center will remainSNA-centric, but the backbone will be TCP/IP.This allows a single protocol across the backbone,while maintaining access to all SNA applications.DLSw+ does not provide native APPN routing,nor does it provide native COS.Consequently, DLSw+ is preferable for networks, in which cost isa key criterion, that have the following characteristics:" A single data center or mainframe" Single links from the branchesIn general, DLSw+ is a lower-cost solution that requires less memory and software.In the vastmajority of networks, DLSw+ will be combined with APPN using APPN only where routingdecisions are critical.With TCP/IP encapsulation, the TCP layer provides the same reliable deliveryas SNA/APPN, but does not provide the native routing and COS.TN3270 transports 3270 data stream inside a TCP/IP packet without SNA headers.Therefore, thissolution assumes that the end station has only a TCP/IP protocol stack and no SNA.Therefore,TN3270 is not an alternative to APPN because APPN assumes the end station has an SNA protocolstack.APPN, like DLSw+, may still be required in the network to route between TN3270 serversand multiple mainframes or data centers.In summary, APPN will frequently be used with DLSw+ in networks when a single backboneprotocol is desired.BAN/BNN provides direct connectivity to the FEP but lacks the multiprotocolcapabilities of other solutions.TN3270 is used only for TCP/IP end stations.Overview of APPNThis section provides an overview of APPN and covers the following topics:" Defining Nodes" Establishing APPN Sessions" Understanding Intermediate Session Routing" Using Dependent Logical Unit Requester/ServerDefining NodesNodes, such as ACF/VTAM, OS/400 and Communications Server/2 (CS/2), can be defined as eithernetwork nodes or end nodes.When you have a choice, consider the following issues:" Network size How large is the network? Building large APPN networks can introducescalability issues.Reducing the number of network nodes is one solution for avoiding scalabilityproblems.For more information on reducing the number of network nodes, see the section Reducing the Number of Network Nodes later in this chapter." Role of the node Is it preferable to have this node performing routing functions as well asapplication processing? A separate network node can reduce processing cycles and memoryrequirements in an application processor.Generally, you should define a network node whenever a routing decision needs to be made.Designing APPN Internetworks 6-7 Overview of APPNAPPN Node IdentifiersAn APPN node is identified by its network-qualified CP name, which has the format netid.name.Thenetwork identifier (netid) is an eight-character name that identifies the network or subnetwork inwhich the resource is located.The network identifier and name must be a combination of uppercaseletters (A through Z), digits (0 through 9), and special characters ($,#,or @) but cannot have a digitas the first character.Establishing APPN SessionsIn order for an APPN session to be established, the following must occur:1 The end user requests a session with an application, which causes the end node to begin theprocess of session establishment by sending a LOCATE message to its network node server.Forsession initiation, the network node server provides the path to the destination end node, whichallows the originating end node to send messages directly to the destination [ Pobierz całość w formacie PDF ]