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2-4 TN3270 Design and Implementation Guide

• Each CIP has up to two Enterprise Systems Connection (ESCON) or two bus-and-tag (parallel) interfaces and

a single virtual interface. The TN3270 Server is installed on the virtual interface. Therefore,each CIP can have

a single TN3270 Server. Because a router can accommodate more than one CIP, each router can support

multiple TN3270 Servers.

• Each CPA has a single ESCON interface and a single virtual interface. As with the CIP, a singleTN3270 Server

can be installed on eachCPA. Becausea routercan accommodatemore thanone CPA, each routercan support

multiple TN3270 Servers.

Note: The subnet of the virtual channel interface must be the same as the subnet of the listening IP addresses.

Otherwise, the router will not know that the listening addresses are directly connected, and will not pass the

routes to the listening addresses to the other routers in the network. Without the address, clients are not be able

to reach the CIP/CPA.

Defining PUs

SNA communication isbased on the concept of PUs and LUs. When decidinghow to conﬁgure a TN3270 Server,

one of the ﬁrst things you must consider is the type of PUs you will use and how you want to deﬁne them. The

TN3270 Server supports two types of PUs:

• Direct PUs—Used in subarea SNA.

• DLUR PUs—Used with Advanced Peer-to-Peer Networking (APPN).

DLUR PUs and direct PUs can coexist on the same CIP/CPA.

The deﬁnition of each direct PU within the router requires a local service access point (SAP) to be deﬁned.

Traditionally, SNA uses SAP04, 08, 0C, andso forth (multiples of four). But the source SAPused by the TN3270

adapter must be an even value. Each PU on a TN3270 adapter on the CIP must, however, have a unique local/

remote media access control (MAC)/SAP quadruple. Ifthe PUs areon the sameadapter and are toconnect to the

same remote MAC (RMAC) and remote SAP (RSAP), then each must have a different link SAP (LSAP).

Therefore, to create dozens of PUs tied to one TN3270 adapter, separate the SAPs by two or four. SAPs are in

hexadecimal format and starting at AA are reserved for other uses (such as Subnetwork Access Protocol [SNAP]

headers, IP, and address resolution protocol [ARP]). If you start with SAP 02 and increment each SAP by two,

youcan tie about120 SAPs toan adapter. Todeﬁne more SAPs,create another adapterand startover with SAP4.

Each direct PU is deﬁned on the CIP/CPA with a listening IP address and a target MAC address that goes to a

particular logical partition (LPAR). The listening address is the IP address that the client addresses when

requesting an LU from the associated PU. Multiple PUs can be deﬁned with the same IP listening address and

thereby create a pool of LUs. This pool of LUs is 255 LUs times the number of PUs with the same listening

address. When a user requests an LU using the listening address that is associated with the group of PUs, the

client willreceive an LU from that pool. Thereis a predeﬁned algorithm that is used to decide what LU the clients

receives. (See the “Monitoring the TN3270 Server” section.) One TN3270 Server can simultaneously service

multiple LPARs if you create a single PU or a pool of PUs per LPAR. To identify which PU or pool of PUs is

associated with which LPAR, create a different listening port for each LPAR.

Figure 2-2 shows an example of three PUs within the same TN3270 Server. Two of the PUs are allocated to the

same listening address. The third PU is assigned to a different listening address.

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Cisco 11.0 BT Manual de usuario Pagina 4