DECnet-Plus
Planning Guide

2.1 Step 1: Document the Current Network Configuration

For example, information on products that cannot make the transition to DECnet-Plus can help determine the configuration of end systems and routers. Identifying all the routers in your network, and determining each one's type, helps you in Step 2 to decide which routing algorithm to use for each Phase V router. Therefore, the more complete your topological map, the more informed your decisions can be.

The decnet_migrate tool provides two commands that, when used together, create a report on the network's configuration:

COLLECT	Collects specified information from specified nodes
REPORT	Creates a report from the data gathered by COLLECT

The tool offers another command, SHOW PATH, that displays the possible paths that node-to-node communication might take through the network, helping to determine what effect the transition has had on the network's communication paths. For complete information about using decnet_migrate, see your network management manual.

To complete Step 1:

• Identify all current:
  • Routers
  • Network management stations
  • Load hosts
  • Name servers
• Compile a list of node names and addresses
• Identify the operating system and DECnet version of each end node
• Identify any hardware or software that cannot make the transition to DECnet-Plus
• Specify the type and area of each router
• Identify any multivendor routers
• For large or complicated networks, separately document the topology for the level 2 network and for each level 1 area

DECnet-Plus offers various transition strategies to suit individual customer networks. Most strategies can be divided into two categories, based on your answer to the following question: Does the network need DECnet Phase V areas?

Your network needs DECnet Phase V areas if:

• You want to take advantage of DECnet-Plus features, especially OSI addressing.
• You need connectivity with multivendor OSI networks.
• You want to take advantage of new DECnet-Plus name service access features.

Your network needs to maintain Phase IV areas if:

• You want to maintain systems that cannot migrate to DECnet-Plus.
• You want to migrate slowly over a period of time.

If your network needs Phase IV addressing, your general strategy will be to move the network partially to a DECnet-Plus environment, at least for the near future. You will have a configuration with both Phase IV areas and DECnet Phase V areas.

If your network is ready to use OSI addresses that are beyond the limits of Phase IV and, therefore, not compatible with Phase IV addresses, your strategy will be to move the network entirely to the DECnet-Plus environment with no Phase IV areas and no Phase IV nodes.

2.2.1 If the Network Is Not Moving Entirely to the DECnet-Plus Environment

If the network needs to remain in a DECnet Phase IV environment for at least one area, an appropriate transition strategy might be that the network has DECnet-Plus systems with Phase IV-compatible addresses. These systems will be able to communicate with the remaining Phase IV nodes.

Another option is that you decide to gain experience using DECnet-Plus in one part of your network before migrating the entire network to DECnet-Plus. You can migrate one area to the DECnet-Plus environment, while the network as a whole operates in the transition environment.

In addition, as part of your "partial" transition strategy, you can use the Local namespace to maintain DECnet-Plus node-name and OSI addressing information until it is more convenient to design and move to a distributed namespace.

Install DECnet-Plus software onto each system that is ready to migrate and assign it a Phase IV-compatible address during the configuration procedure. The network transition plan, then, would highlight the order of migration for individual nodes.

2.2.2 If the Network Is Moving Entirely to the DECnet-Plus Environment

If you need at least one DECnet Phase V area, determine whether or not the entire network can move to DECnet-Plus. For example, consider a small, single-area LAN of approximately 20 nodes. If it has no Phase III nodes or other products that cannot migrate, you can migrate it entirely to a DECnet-Plus environment by installing DECnet-Plus software on every end system.

2.3 Step 3: Develop a New Network Configuration

To develop a network configuration, make the following decisions:

• Which routing algorithm will each Phase V router system run?
• Which systems will be end systems and which will be routers?
  For example, existing DECnet Phase IV routing nodes can:
  • Remain at Phase IV and continue to perform routing in a Phase IV area
  • Transition to DECnet-Plus and function as end nodes (assuming you intend to use dedicated routers)
  • Transition to DECnet-Plus for OpenVMS Version 7.1 and continue to function as host-based routers running the Routing Vector protocol
• Will the network use Phase IV-compatible addressing, OSI addressing that is beyond Phase IV limitations, or both?

Your planning activities include:

• Evaluating the possible new network configurations and choosing which to implement
• Considering the addition of multivendor systems to the network
• Planning the network addressing scheme
• Planning routing
  For complete routing configuration information, see the documentation set of your Phase V router.

As you create your new network configuration, review the information in Chapter 1 for:

• Products that will not migrate to DECnet-Plus
• DECnet-Plus incompatibility with Phase III
• Routing products

In addition, to determine the configuration of end systems and routers, use the following information to guide your decisions:

• If you plan to migrate level 1 routers to use link state, you can convert Phase IV PDP-11 and DECnet-Plus for OpenVMS VAX routing nodes to end systems. However, you must remove DECrouter 200 and DECSA routers from the DECnet Phase V area.
• DECnet-Plus supports multivendor OSI-compliant end systems in the network.
• DECnet-Plus supports the following configurations, each with distinct advantages that should be considered for your transition:
  • One LAN with a single, extended-area
  • LANs without routers
  • Multicircuit end systems
  
  For detailed information about planning routing configurations, see the documentation set of your Phase V routing product.

In the Phase IV environment, LANs can have multiple areas. In the DECnet-Plus environment, however, a LAN can have only one DECnet Phase V area address: an area over 63. This area can have a virtually limitless number of systems, but they all must reside in that single DECnet Phase V area address space. In the transition environment, you can give a LAN multiple areas if the area numbers are within Phase IV limits: 63 or less.

If you plan to migrate a multiple Phase IV-area LAN to the DECnet-Plus environment, during the migration, the DECnet-Plus end systems will be multihomed to a Phase IV-compatible area as well as to an area in the larger DECnet Phase V address space.

2.3.1.2 End-System-Only LAN Configurations

A LAN can consist of end systems only. A DECnet-Plus LAN without routers has virtually no limit on the number of systems it can contain.

The end system to intermediate system (ES-IS) routing exchange protocol (ISO 9542) provides the process by which end nodes communicate with routers, or with each other, to exchange configuration information. In a DECnet-Plus end-system-only network, end systems on a LAN use the ES-IS protocol to communicate directly with each other without depending on a router.

DECnet-Plus end systems communicate directly by using a multicast address called "All End Systems." All end systems normally listen to this address for Router Hello messages, identifying routers to end systems. An end system also uses this multicast address when sending a packet to an end system for which it does not have a cache entry.

When an end system receives a multicast data packet that belongs to itself, it makes a cache entry for the sending end system and sends back an End System Hello, which causes the other end system to make an entry in its cache. When it has another packet to send, the end system checks its cache and uses the cached address instead of the multicast address.

In a LAN with only end systems, these systems can have Phase IV-compatible addresses, extended DECnet Phase V addresses, or a mixture of both. You can allow end systems to autoconfigure their OSI addresses, or you can manually assign them Phase IV-compatible addresses.

When end systems do not have an assigned Phase IV address, they construct an NSAP for each transport operating over routing. Each NSAP is constructed by concatenating the default local area address (49::00-40), the node ID, and the selector representing the transport (NSP or OSI transport). The Figure 2-1 illustrates a network address, or NSAP, of an autoconfigured end system in an end-system-only network:

Figure 2-1 Autoconfigured End System NSAP

When an end system does have an assigned Phase IV address, it constructs an NSAP for each transport operating over routing by concatenating the local AFI (49), 2 octets containing the area portion of the Phase IV address, a Phase IV-style LAN address (aa-00-04-00-xx-xx), and the selector representing the transport. Figure 2-2 illustrates this type of NSAP.

Figure 2-2 Assigned Phase IV Address NSAP

The corresponding Phase IV address is 12.23.

Instead of allowing an end system to autoconfigure its address, you can assign it an OSI address. To manually configure, use the DECnet-Plus configuration utility, net$configure.com (for OpenVMS) or decnetsetup (for Digital UNIX), or use NCL. For details, see your network management guide.

2.3.1.3 Multicircuit End-System Configurations

A Phase IV end node can have multiple circuits to one or several adjacent nodes, but only one of these circuits can be active at a time. Among Phase IV nodes, only routers have multiple active circuits. DECnet-Plus end systems, on the other hand, can be multicircuited. DECnet-Plus multicircuit end systems can have up to four multiple active circuits to either the same or different subnetworks.

A subnetwork is a communications network, within a group of interconnected networks, of OSI systems that use a common addressing format and that forms an autonomous whole. Examples are

X.25 packet switched networks, HDLC data links and ISO 8802.3 LANs.

These restrictions apply to multicircuit configurations:

• All circuits must be in the same area; the entire set of area addresses for the multicircuit end nodes that correspond to a single network area.
• The circuits must all have the same amount of usable bandwidth.
• All the circuits should provide approximately the same connectivity to other nodes over approximately equivalent paths. Do not use multiple circuits to connect disjointed networks.

Multicircuit end systems do not forward packets to other systems. However, the Routing layer of a DECnet-Plus end system receives information from routers about paths to destinations. The end system gets this information by using the ES-IS protocol to communicate with routers in its area. The routers give the end system information about direct paths to destinations, that is, paths that do not require forwarding the packet. The end system stores the information in a cache and uses it to select an appropriate circuit for sending data to a particular destination. If an end system has no information about a certain destination, it selects a router at random and forwards the data to that router.

Use the following guidelines when you configure multicircuit end systems:

• Configure the circuits to routers with paths that are fairly similar in cost.
  The preferable configuration of end-system circuits is such that information in the cache is on the most efficient paths to a destination. Multicircuit end systems, unlike routers, store no information on path costs. The only decision about paths an end system makes is to choose a direct path, as opposed to an indirect path, to a destination. Multicircuit end systems choose circuits in the following order:
  1. Circuits by which the packet can reach the destination directly, that is, without being forwarded through other systems. The multicircuit end system gets information from routers about direct paths and stores the information in its end-system cache.
     When two or more circuits provide direct paths, the end system selects a circuit on a round-robin (alternating) basis.
  2. Circuits by which the packet can reach the destination indirectly. The end system uses these circuits if it knows of no direct path to the destination.
     Again, when two or more circuits provide indirect paths, the end system selects a circuit on a round-robin (alternating) basis.
• If you plan to change the configuration of the area, first assess the effect it could have on the operation of the circuits of any multicircuit end systems.
  An end-system cache has a timer on its circuit information. When the timer expires, the end system gets new information about paths. If the configuration has changed, the path information may not be similar in cost any more.

  DECnet-Plus for OpenVMS and DECnet/OSI for Digital UNIX end systems with multiple active circuits provide redundancy and increased data throughput. An end system with multiple circuits to an Ethernet LAN, for example, provides a guarantee that if one circuit fails, this system still has access to the LAN. There is no gain in data throughput, however, since both circuits go to the same LAN.

  You can also configure a multiple-active-circuit end system with its circuits to different LANs. Figure 2-3 shows an end system with circuits to two different Ethernet LANs. This configuration is useful where reliability is critical such as in a network that supports banking applications, for example. This configuration also provides for increased data throughput, since circuits to two different LANs can carry double the number of packets.

  Figure 2-3 Multicircuit End System with Circuits to Two Ethernet LANs

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  Figure 2-4 shows a configuration in which an end system has two active Digital Data Communications Message Protocol (DDCMP) circuits to different routers on a LAN. This configuration could provide redundancy in a situation where, for example, there is concern about disturbances on one of the telephone lines.<>

  Figure 2-4 Multicircuit End System with Two DDCMP Circuits

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  Though you can configure circuits to either the same or a different subnetwork, you can enable the Phase IV address of only one circuit per LAN. To configure a multicircuit end system with a Phase IV address and one or more circuits to the same LAN, take the following steps:

  1. If you have not already done so, install the Ethernet hardware necessary for each of the system's connections to the LAN.
  2. During the DECnet-Plus configuration process, assign the system a Phase IV address. Also, choose the option that allows the system to autoconfigure its network address.
  3. After configuration, on all but one of the Ethernet circuits, set the Routing Circuit entity characteristic enable phase IV address to false . The one circuit with this attribute set to true has its Ethernet address set to a Phase IV Ethernet address. All other circuits retain the address of their Ethernet controller.
     This example sets the enable phase IV address routing characteristic to FALSE on the routing circuit csmacd-1 of the local node:

     ncl> set routing circuit csmacd-1 enable phase iv address=false 
     

  You can set the Routing characteristic enable phase IV address in two ways:

  • Answer the installation prompts appropriately.
  • Edit the Routing layer initialization script and add the commands to set the characteristic. When you next reboot the system, the initialization process runs the script and enables the Phase IV address on only one circuit.
    For for OpenVMS, the initialization script is:
    sys$manager:net$routing_startup.ncl
    For Digital UNIX, the initialization script is:
    /var/dna/scripts/start_routing.ncl

  2.3.2 Including Multivendor Systems in the Network

  DECnet-Plus software allows OSI-compliant systems from other vendors to participate as end systems in the DECnet Phase V network. Use the following guidelines when you add other vendors' OSI-compliant systems to your network:

  • You can include only OSI-compliant systems.
  • You can include OSI end systems in a DECnet Phase V area (or network). You can also include them in a Phase IV area (or network operating in a transition environment) if you can configure their addresses as Phase IV-compatible addresses.
  • Phase V routers treat the multivendor OSI end system as they do any DECnet-Plus end system.
  • You must have DECnet-Plus paths to the multivendor OSI end systems. This means that the network is configured so every possible connection path to the OSI end system has only Phase V routers, not Phase IV routers.
  • Do not register multivendor OSI end systems in the DECdns namespace. Only DNA applications and DNA network management use node-name objects in the namespace; OSI applications use their own private naming databases. Register the multivendor OSI end systems in those OSI databases as directed by your OSI application documentation.
  • To include a multivendor OSI end system in the network, check that the system meets one of the following conditions:
    • The end system uses the ES-IS protocol and the end system's address can be configured. See the other vendor's documentation for this information.
    • The end system does not use the ES-IS protocol but resides on a LAN for which there is an OSI router and the NSAP address can be configured.
    • The end system does not use the ES-IS Protocol and you cannot configure its NSAP address; but you can attach the OSI-compliant end system to a level 2 Phase V router system. This router must be running link state if the OSI-compliant end system's address is not Phase IV-compatible.
    • You attach the OSI-compliant end system through an X.25 dynamically assigned circuit.
      On either the router or the end system, you create a routing circuit reachable address entity for the OSI-compliant end system.

  2.3.3 Using the Inactive Network Layer Protocol

  DECnet-Plus provides support for the inactive Network layer protocol specified in ISO 8473. The inactive subset bypasses the Network layer, running transport directly over a data link connected to a LAN. You can use this configuration when the source and destination end systems are on the same LAN.

  Consider these guidelines before using the inactive Network layer protocol:

  • Only one transport module can make use of the inactive subset. By default, this is OSI transport, as specified by the preset routing characteristic inactive selector.
  • All end systems using the inactive subset should specify the same inactive area address.

  To configure the inactive subset on a circuit, use NCL to set the circuit attribute inactive area address. The area address portion of the NSAP address is placed in this set, as shown in Figure 2-5.

  Figure 2-5 Area Address Portion of the NSAP Address

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  This command configures the inactive subset on circuit-1:

  ncl> set routing circuit circuit-1 inactive area address {49::ff-00} 
  

  You can assign only one inactive area address to a circuit.

  During transmission, when a service data unit (SDU) is passed to an end system's Network layer, transport provides a destination NSAP. If the area address portion of the destination NSAP matches the inactive area address assigned to the circuit, then routing uses the inactive Network layer protocol and passes the SDU directly to the Data Link layer, specifying the ID portion of the destination NSAP as the destination data link address.

  If an end system's Network layer receives a protocol data unit (PDU) with the inactive Network layer protocol header on a circuit that has the inactive area address set, then routing passes the SDU up to transport.

  In addition, routing calculates the source and destination NSAPs as follows:

  • Source NSAP
    Figure 2-6 illustrates a source NSAP.

    Figure 2-6 Source NSAP

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  • Destination NSAP
    The numerically lowest NSAP in the set of NSAPs assigned to the port for which the SDU is bound.

  If an end system's Network layer receives a PDU with an inactive Network layer protocol header on a circuit that does not have the inactive area address set, then the PDU is dropped.

  2.3.4 Planning Addressing

  When planning your network's addressing scheme, determine the need for unique IDP and DECnet Phase V addresses, which, in turn, depends on the general transition strategy you chose in Step 2.

  2.3.4.1 Do You Need a Unique IDP for Your Network?

  DECnet-Plus software includes a default IDP, which has the local AFI of 49 and a null IDI. The local AFI and null IDI means that the IDP is intended for use within a private network. Therefore, the local AFI is useful only in a network not connected to any external networks.

  As network manager, consider whether the default IDP is sufficient for your network. If you plan to connect your network to other networks, you must obtain a unique IDP. Consider obtaining a unique IDP if there is a possibility that, in the future, you might connect your network to other networks. Otherwise, the default IDP is sufficient.

  For information about obtaining a unique IDP for your network, see Section 4.7. If you change your network's IDP, use the decnet_register tool (see your network management guide).

  2.3.4.2 Do You Need Extended OSI Addresses?

  The general transition strategy you planned in Step 2 determines your decision about the need for OSI addressing that goes beyond Phase IV address limitations:

  • If all of your network is moving to the DECnet-Plus environment, you have already decided to use OSI addressing. This strategy requires that routers run the link state protocol. See Section 2.3.4.3 for addressing guidelines.

  • If none of your network is moving to the DECnet-Plus environment, then you have already decided to use Phase IV-compatible addressing for all systems. With this strategy, you can use the default IDP that comes with the DECnet-Plus software. In this case, you can ignore the considerations in Section 2.3.4.3 until you are ready to move the network to OSI addressing.
  • If part of your network is moving to the DECnet-Plus environment, then you will make address decisions on an area-by-area basis. Whether an area will be a Phase IV or DECnet Phase V area affects the decisions you make as to the area's configuration, addressing, and routing algorithm. See Section 2.3.4.3 for addressing considerations.

  2.3.4.3 Considerations for a Network with DECnet Phase V Areas

  A network with one or more DECnet Phase V areas requires well-planned addresses because:

  • There are differences between Phase IV and OSI addresses, and communication between Phase IV nodes and DECnet-Plus systems depends on coordinating those addresses (see Section 1.3.1).
  • Using extended OSI addresses requires that routers run link state (see Section 2.3.5).

  Also use the following guidelines when planning addresses:

  • If an area has Phase IV nodes, you must assign Phase IV addresses to all the Phase V routers in the area.
  • A network area can use OSI addressing only when all systems are DECnet-Plus systems and all routers run link state or when Phase IV nodes communicate with a small number of DECnet-Plus systems that have Phase IV-compatible addresses.
  • For a DECnet-Plus system to communicate with another DECnet-Plus system with an extended address, the path between the systems must be a DECnet-Plus path. A DECnet-Plus path is a routing path on which all routers are running link state.
  • In a OSI address, the area address equals the IDP + PreDSP + LOC-AREA fields. Phase IV nodes do not recognize the concept of an IDP. Therefore, they cannot communicate outside of their own network. A Phase IV node cannot connect to any node in another network that has a different IDP, not even another Phase IV node.
  • When the network area is ready to use extended OSI addressing, assign these addresses to the Phase V routers, which must be running the link state protocol. Assigning OSI addresses to the Phase V routers makes it possible for end systems in the area to autoconfigure their node addresses.
  • If your network has a unique IDP, you must specify that IDP as part of the node address at either of the following times:
    • During the configuration of every router, if you plan that the end nodes will autoconfigure their addresses
    • During the configuration of every system, if you plan that the end nodes will not autoconfigure their addresses

  2.3.5 Planning Routing

  When you plan routing configurations, use the following guidelines:

  • Phase V router products can support either the Phase IV routing vector protocol or the DECnet Phase V link state protocol on level 1 and level 2.
  • All level 1 routers in an area must run the same routing protocol.
    For example, if one level 1 router runs routing vector which is a DECSA router that cannot migrate to DECnet-Plus, then all routers in the area must run routing vector.
  • To use OSI addresses, all level 1 routers must be running link state.
  • For end systems to autoconfigure their addresses, all level 1 routers must run link state. Also, during configuration, you must have assigned DECnet Phase V area addresses to the level 1 routers.
  • You must have DECnet-Plus routing paths:
    • Among all DECnet-Plus name servers
    • Between each DECnet-Plus system and OSI end system with which it communicates, if they have non-Phase-IV addresses
    • Between two OSI end systems that need to communicate, if they have non-Phase-IV addresses.
  • Routers in the level 2 network can run different routing algorithms. To allow for a level 2 router running routing vector to communicate with a level 2 router running link state, the two routers must meet the following requirements:
    • A router running routing vector must be connected directly to a router running link state.
    • A router running link state must have an interphase link entry in its reachable-address table for the router running routing vector.
      See your network management guide for information about interphase routing and how to use the decnet_migrate tool's create ipl_initialization_file command that helps you set up interphase links.
  • You can use NCL to set the routing algorithm. For example, the following command sets the routing algorithm to link state on adjacent routing node .ultra.router:

    ncl> set node .ultra.router routing manual L1 algorithm link state algorithm 
    

  • When you switch the routing algorithm, for example, in an area where all systems will have OSI addresses, all routers must change algorithms at the same time or you lose connectivity in the area.

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