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Configuring DECnet

Configuring DECnet

This chapter describes how to configure our implementation of the DECnet routing protocol. For a complete description of the commands in this chapter, refer to the "DECnet Commands" chapter of the Network Protocols Command Reference, Part 3.


Note Not all Cisco access servers support the DECnet protocol. For more information, refer to the Release Notes for Cisco IOS Release 11.2.

DECnet Configuration Task List

To configure DECnet routing, complete the tasks in the following sections. Only the first task is required; the remaining tasks are optional.

See the "DECnet Configuration Examples" section at the end of this chapter for configuration examples.

Enable DECnet Routing

In order to enable DECnet routing, you must complete the tasks in the following sections:

Enable DECnet Phase IV Routing

To enable DECnet Phase IV routing, perform the following task in global configuration mode:

Task Command
Enable the DECnet Phase IV routing protocol on a global basis. decnet [network-number] routing decnet-address

For each interface on which DECnet routing is configured, the decnet cost command is required.

A DECnet host exists as a node in an area. An area spans many routers, and a single interface can have many areas attached to it. Therefore, if a router exists on many cables, it uses the same area and node for itself on all of them. Note how this differs from other routing protocols, where each interface is given a different internetwork address. Figure 9 shows the DECnet approach.

Enabling DECnet changes the MAC addresses of the router's interfaces. This is not a problem on routers equipped with nonvolatile memory. On systems that attempt to get their Internet Protocol (IP) network addresses from network servers instead of from nonvolatile memory, there might be a problem with the hardware addresses changing and confusing other IP-speaking hosts. If you are attempting to use DECnet on such a configuration, be sure to set all global DECnet parameters before enabling DECnet routing on the interfaces.

With DECnet Phase IV Prime, the change of MAC addresses is not an issue because you can change the MAC address of the interface.


Note If you plan to use DECnet
and Internet Packet Exchange (IPX) routing concurrently on the same interface, you should enable DECnet routing first, then enable IPX routing without specifying the optional MAC address. If you do this in the reverse order (that is, enable IPX, then DECnet), IPX routing will be disrupted.

Once you have enabled DECnet routing, you can obtain MAC addresses by using the show interfaces EXEC command. To disable DECnet routing, use the no decnet routing command.


Figure 9:
DECnet Nodes and Area


Enable DECnet Phase IV Prime Routing

DECnet Phase IV requires that a MAC station address be constructed using DECnet addressing conventions, with a standard high-order byte string (AA-00-04-00) concatenated with the byte-swapped DECnet node address. This can cause problems in configurations in which DECnet nodes must coexist with systems running protocols that have other MAC address restrictions.

DECnet Phase IV Prime allows an arbitrary MAC address on the LAN. An address can be assigned globally (that is, assigned by the IEEE), or it can be assigned locally by a system administrator.

To enable or disable DECnet Phase IV Prime, perform (in global configuration mode) one of the following tasks:

Task Command
Specify Phase IV Prime routing. decnet [network-number] routing iv-prime decnet-address
Stop DECnet Phase IV or
Phase IV Prime routing.
no decnet routing

For each interface on which DECnet routing is configured, the decnet cost command is required.

Optionally, you can map a DECnet multicast address to a Token Ring functional address other than the default functional address. To do so, perform the following task in interface configuration mode:

Task Command
Specify the type of multicast address and the functional address to which the multicast ID will map. decnet multicast-map multicast-address-type functional-address

Assign a DECnet Cost to Each Interface

After you have enabled DECnet routing, you must assign a cost to each interface over which you want DECnet to run. Assigning a cost to an interface enables DECnet on the interface and, using a standard formula, assigns a different MAC address than that "burned in" by the manufacturer. This section describes how to assign a cost to each interface.

DECnet routing decisions are based on cost, an arbitrary measure used to compare paths on the internetwork. Costs are based on such measures as hop count or media bandwidth. The lower the cost, the better the path. You must assign a cost to each interface.

To assign a cost to each interface for DECnet Phase IV Prime, perform the following task in interface configuration mode:

Task Command
Assign a cost to an interface. decnet cost cost-value

Most DECnet installations have individualized routing strategies for using costs. Therefore, check the routing strategy used at your installation to ensure that the costs you specify are consistent with those set for other hosts on the network.

Figure 10 shows four routers (three Ethernets) and the various routes linking them. Each link has a different cost associated with it. The least-expensive route from Router 7 to Router 20 is via Router 12.


Figure 10: DECnet Cost Values


Specify the DECnet Node Type

DECnet routing nodes are referred to as either Level 1 or Level 2 routers. You must specify the router's node type. A Level 1 router exchanges packets with other end nodes and routers in the same area and ignores Level 2 packets; this is called intra-area routing. Level 2 routers participate in the DECnet routing protocol with other routers and route packets to and from routers in other areas; this is called interarea routing. Level 2 routers also act as Level 1 routers in their own area.

The keyword area indicates a Level 2, interarea, router. The keyword routing-iv indicates a Level 1, intra-area, router; this is the default. In Level 1 mode, the Cisco IOS software sends packets destined for other areas to a designated interarea router, which forwards them outside the area.

To specify the node types, perform one of the following tasks in global configuration mode:

Task Command
Specify an interarea node type of the router. decnet [network-number] node-type area
Specify an intra-area node type of the router. decnet [network-number] node-type routing-iv

For an example of how to configure DECnet, see the "DECnet Example" section at the end of this chapter.

Enable Concurrent Routing and Bridging

You can route DECnet on some interfaces and transparently bridge it on other interfaces simultaneously. To do this, you must enable concurrent routing and bridging. To configure an interface for concurrent routing and bridging, you use the bridge crb command.

To enable concurrent routing and bridging, perform the following task in global configuration mode:

Task Command
Enable concurrent routing and bridging. bridge crb1

1 This command is documented in the "Transparent Bridging Commands" chapter of the Bridging and IBM Networking Command Reference.

Configure DECnet on Token Rings

If any Cisco routers are running Release 9.0 or earlier, you can use the Token Ring as a backbone or transit network for DECnet routing but you cannot communicate with non-Cisco DECnet nodes on the Token Ring.

If all Cisco routers are running Release 9.1 or later, you can set DECnet encapsulation to allow Cisco interoperation with non-Cisco equipment.

If you have both 9.0 and 9.1 routers in the same network, and you want them to interoperate, you must set the encapsulation type to pre-dec on the 9.1 routers.

To run DECnet on Token Ring interfaces, perform the following tasks in interface configuration mode:

Task Command
Step 1 Enable DECnet on the Token Ring interface, and then enter interface configuration mode. interface tokenring number1
Step 2 Configure the DECnet encapsulation mode for the specified interface. decnet encapsulation {pre-dec | dec}

1 This command is documented in the "Interface Commands" chapter of the Configuration Fundamentals Command Reference.

Use the keyword dec with routers running Release 9.1 or later. Use the keyword pre-dec with routers running Release 9.0 or earlier, or in a network where routers running 9.0 and 9.1 must interoperate.

Configure Address Translation

If you set up multiple networks, we recommend that you configure address translation in order to avoid problems with duplicate addressing between networks. If you have multiple DECnet networks, you must establish an address translation table for selected nodes between networks. This eliminates any potential problems of duplicate addressing occurring between networks. The ATG allows you to define multiple DECnet networks and map between them.

Map Between Networks

Configuring ATG allows the Cisco IOS software to route traffic for multiple independent DECnet networks, and to establish a user-specified address translation for selected nodes between networks. Address translation allows connectivity between DECnet networks that might not otherwise be possible because of address conflicts (duplicate addresses) between them. Configuring ATG can be done over all media types.

When you use ATG, all the DECnet configuration commands implicitly apply to network number 0 unless you specify otherwise.

To translate a virtual DECnet address to a real network address, perform the following task in global configuration mode:

Task Command
Establish a translation entry to translate a virtual DECnet address to a real DECnet address for the router. decnet first-network map virtual-address second-network
real-address

To display the address mapping information used by the DECnet ATG, use the show decnet map EXEC command.

For a simple example of how to configure address translation, see the "Address Translation Example" section at the end of this chapter.

Make a "Poor Man's Routing" Connection

As an additional feature and security precaution, DECnet "Poor Man's Routing" can be used between nodes outside of the translation map, provided those nodes have access to nodes that are in the map. For example, as illustrated in Figure 11 in the "Address Translation Example" section at the end of this chapter, a user on node B could issue the following VMS operating system command:

$ dir A::D::E::

When a Poor Man's Routing connection is made between two networks, only the two adjacent nodes between the networks will have any direct knowledge about the other network. Application-level network access can then be specified to route through the connection.


Note We do not support Poor Man's Routing directly; the intermediate nodes must be VMS systems with Poor Man's Routing enabled in the file-access language.

Specify Name-to-DECnet Address Mapping

You can define a name-to-DECnet address mapping, which can be used instead of typing the set of numbers associated with a DECnet address.

To define a name-to-DECnet address mapping, perform the following task in global configuration mode:

Task Command
Define a name-to-DECnet address mapping. decnet host name decnet-address

The assigned DECnet name is displayed, where applicable, in the output of the decnet route and show hosts EXEC commands.

Enable Phase IV-to-Phase V Conversion

Routers that have conversion enabled advertise reachability to both Phase IV and Phase V hosts in both Phase IV and Phase V routing updates. If you have Phase IV hosts in Phase V networks and vice versa, you must enable Phase IV-to-Phase V conversion (and vice versa) in order for all nodes to communicate with each other. To enable DECnet conversion, you must have both DECnet and ISO CLNS configured on your router; then perform the following task in global configuration mode:

Task Command
Enable DECnet Phase IV-to-Phase V (and vice versa) conversion on the router. decnet conversion nsap-prefix

Verify that the area you specify in the decnet conversion global configuration command is the same as the area you specified in the ISO CLNS address. You must also enable CLNS on all interfaces, even if the router has only Phase IV hosts on some of the interfaces. This enables information about those routers to be included in link-state packets and, consequently, enables other routers to be informed about the routers connected by that interface.

For an example of how to enable a Phase IV area through an OSI backbone, see the "Phase IV-to-Phase V Conversion Example" section at the end of this chapter.

Propagate Phase IV Areas through an OSI Backbone

One limitation of the Phase IV-to-Phase V conversion has been the inability to propagate Phase IV area routes through OSI clouds. Using the "advertise" feature, you can explicitly configure any DECnet Phase IV areas that you want to propagate outward. You configure the border routers at the Phase IV/Phase V junction.

When distant routers send a packet destined across the cloud to a border router, the router converts the route and sends it as an OSI packet. In order for the converting router to have the corresponding OSI entry to which to convert the Phase IV packet, the other border router at the Phase IV/V junction must inject static discard routes. In this way, the first router converts the packet from Phase IV to Phase V, sending it through the cloud. At the other end, the router advertising the static discard route converts the packet back to Phase IV and discards the Phase V packet. In effect, a fake entry is created in the Phase IV area table to propagate this information to other routers. This entry will not overwrite a native Phase IV entry if one already exists in the table.

To enable Phase IV areas to propagate through an OSI backbone on the router, perform the following task in global configuration mode:

Task Command
Enable DECnet Phase IV areas to propagate through an OSI backbone on the router. decnet advertise decnet-area hops cost

To enable the border router at the far end to convert the Phase V packet back to Phase IV, it must advertise a static discard route. To configure the far border router, perform the following task in global configuration mode:

Task Command
Advertise a static discard route on the far-end border router. clns route nsap-prefix discard1

1 This command is documented in the "ISO CLNS Commands" chapter of the Network Protocols Command Reference, Part 3.

For an example of how to enable a Phase IV area through an OSI backbone, see the "Phase IV Areas through an OSI Backbone Example" section at the end of this chapter.

Establish the Routing Table Size

You can configure the maximum number of addresses and areas allowed in the Cisco IOS software routing table. It is best to keep routing updates small. All areas or nodes that cannot be reached must be advertised as unreachable. When configuring the routing table size, indicate the maximum node and area numbers that can exist in the network. In general, all routers on the network should use the same values for maximum addresses and nodes.

To establish the routing table size, perform either or both of the following tasks in global configuration mode:

Task Command
Set the maximum node address that can exist in the network. decnet [network-number] max-address value
Set the largest number of areas that the Cisco IOS software can handle in its routing table. decnet [network-number] max-area area-number

Configure Level 1 Routers

Perform any of the tasks in the following section for the routers you have configured as Level 1 (intra-area) routers. In Level 1 mode, the router sends packets destined for other areas to a designated interarea router, which forwards them outside the area.

Set Areas as Unreachable

You can set the maximum cost that the Cisco IOS software considers usable for intra-area routing. The software ignores routes within its local area that have a cost greater than the value you specify.

Set Maximum Number of Hops

You can also set the maximum number of hops (or traversal of different paths) that the Cisco IOS software considers usable for intra-area routing. The software ignores routes within its local area that have a value greater than you specify.

To set certain intra-areas as unreachable based on cost value or hop count, perform either or both of the following tasks in global configuration mode:

Task Command
Set the maximum cost value for
intra-area routing.
decnet [network-number] max-cost cost
Set the maximum hop count value for intra-area routing. decnet [network-number] max-hops hop-count

Configure Level 2 Routers

Perform any of the tasks in the following section for the routers you have configured as Level 2 (interarea) routers. In Level 2 mode, the Cisco IOS software sends packets destined for other areas via the least-cost path to another interarea router.

Set Areas as Unreachable

You can set the maximum cost for a usable route to a distant area. The Cisco IOS software treats as unreachable any route with a cost greater than the value you specify.

Set Maximum Number of Hops

You can also set the maximum number of hops for a usable route to a distant area. The Cisco IOS software treats as unreachable any route with a hop count greater than the value you specify.

To set certain interareas as unreachable based on cost value or hop count, perform either or both of the following tasks in global configuration mode:

Task Command
Set the maximum cost specification value for interarea routing. decnet [network-number] area-max-cost value
Set the maximum hop count value for interarea routing. decnet [network-number] area-max-hops value

Specify Designated Routers

You can determine the router to which all end nodes on an Ethernet communicate if they do not know where else to send a packet. This router is called the designated router and is the router with the highest priority. When two or more routers on a single Ethernet in a single area share the same highest priority, the router with the highest node number is selected. You can reset the priority to help ensure that it is elected designated router in its area. This is specified on a per-interface basis.

To specify designated routers, perform the following task in interface configuration mode:

Task Command
Assign or change a priority number to a router on a per-interface basis to receive packets for which no destination is specified. decnet router-priority value

Configure Static Routing

Static routing is used when it is not possible or desirable to use dynamic routing. The following are some instances of when you would use static routing:  


Note An interface that is configured for static routing cannot reroute around failed links.

To configure static routing, complete any of the tasks in the following sections:

Configure a Static Route

You can configure a specific static route and apply it globally even when you use dynamic routing.

To apply a specific static route globally, perform the following task in global configuration mode:

Task Command
Configure a specific static route. decnet route decnet-address next-hop-address [hops] [cost]

Configure a Static Route for an Interface

You can select a specific interface for a specific static route when you do not know the address of your neighbor.

To apply a specific static route to a specific interface, perform the following task in global configuration mode:

Task Command
Configure a specific static route for a specific interface. decnet route decnet-address next-hop-type number [snpa-address] [hops [cost]]

Configure a Default Static Route

You can configure a default static route and apply it globally, even when you use dynamic routing.

To apply a default static route globally, perform the following task in global configuration mode:

Task Command
Configure a default route. decnet route default next-hop-address [hops [cost]]

Configure a Default Static Route for an Interface

You can configure a specific interface for a default static route when you do not know the address of your neighbor.

To apply a default static route to a specific interface, perform the following task in global configuration mode:

Task Command
Configure a specific default route for a specific interface. decnet route default next-hop-type number [snpa-address] [hops [cost]]

Configure DECnet Static Route Propagation

When you use static routes or default static routes, you can specify whether the static routes are propagated. By default, DECnet static routes will not be propagated to other routers.

To enable or disable static route propagation, perform the following tasks in global configuration mode:

Task Command
Enable static route propagation. decnet propagate static
Disable static route propagation. no decnet propagate static

Control Access to DECnet Networks

We provide several layers of access control for network security. You can complete any or all of the tasks in the following sections:

Create an Access List Based on Source Addresses

You can configure lists globally to control access by source addresses. The standard form of the DECnet access list has a source DECnet address followed by a source-mask address, with bits set wherever the corresponding bits in the address should be ignored. DECnet addresses are written in the form area.node. For example, 50.4 is area 50, node 4. All addresses and masks are in decimal notation.

To create a standard DECnet access list, perform the following task in global configuration mode:

Task Command
Create an access list to restrict access to a single address. access-list access-list-number {permit | deny} source
source-mask

To disable the list, use the no access-list command.

Create an Access List Based on Source and Destination Addresses

The extended form of the DECnet access list has a source DECnet address and mask pair, followed by a destination DECnet address and mask pair.

To configure an extended DECnet access list, perform the following task in global configuration mode:

Task Command
Create an extended access list for several addresses. access-list access-list-number {permit | deny} source
source-mask
[destination destination-mask]

To disable the extended access list, use the no access-list command.

Add Filters to Access Lists

DECnet access lists can be used to filter connect initiate packets. With these packets, you can filter by DECnet object type, such as MAIL.

To add ilters to access lists, perform the following task in global configuration mode:

Task Command
Add filtering (by DECnet object type) to an access list. access-list access-list-number {permit | deny} source source-mask
[destination destination-mask {eq | neq} [[source-object]
[destination-object] [identification]] any]

Configure Access Groups

You can restrict access to specific interfaces by applying an access list to them. Interfaces that are associated with the same access list are considered to be an access group.

To configure access groups, perform the following task in interface configuration mode:

Task Command
Assign an access list to a specified interface. decnet access-group access-list-number

Configure Routing Filters

You can control access to hello messages or routing information being received or sent out on an interface. Addresses that are not in the access list are shown in the update message as unreachable.

To configure routing filters, perform either or both of the following tasks, as needed, in interface configuration mode:

Task Command
Control access to hello messages or routing information received on a specified interface. decnet in-routing-filter access-list-number
Control access to routing information being sent out on a specified interface. decnet out-routing-filter access-list-number

Enhance DECnet Performance

To optimize internetwork performance, complete any or all of the tasks in the following sections:

Set Maximum Equal-Cost Paths

You can set the maximum number of equal-cost paths to a destination on a global basis. Limiting the number of equal-cost paths can save memory on routers with limited memory or with very large configurations. Additionally, in networks with a large number of multiple paths and end systems with limited ability to cache out-of-sequence packets, performance might suffer when traffic is split between many paths.

To set maximum equal-cost paths, perform the following task in global configuration mode:

Task Command
Set the maximum number of equal-cost paths to a destination. Paths are set in the routing table. decnet [network-number] max-paths value

Use the show decnet route EXEC command to display the first hop route to a specified address and to show all equal-cost paths to a single destination.

Establish Selection for Paths of Equal Cost  

You can establish one of two methods for selecting among paths of equal cost on the router: on a round-robin basis, which is the default, or by configuring the Cisco IOS software so that traffic for any higher-layer session is always routed over the same path.

In the round-robin or normal mode, the first packet is sent to the first node, the second packet to the second node, and so on. If the final node is reached before all packets are sent, the next packet in line is sent to the first node, then to the second node, and so forth.

The interim mode supports older implementations of DECnet (VMS Versions 4.5 and earlier) that do not support out-of-order packet caching. Other sessions might take another path, thus using equal-cost paths that a router might have for a particular destination.

To select normal or interim mode on the router, perform one of the following tasks in global configuration mode:

Task Command
Specify that traffic is routed over equal-cost paths on a round-robin basis. decnet path-split-mode normal
Specify that traffic is always routed over the same path. decnet path-split-mode interim

Set Maximum Visits

You can determine the number of times that a packet can pass through a router. The Cisco IOS software ignores packets that have a value greater than the amount of visits you specify. Digital recommends that the value be at least twice the number of maximum hops, to allow packets to reach their destinations when routes are changing.

To set the number of times a packet can pass through a router, perform the following task in global configuration mode:

Task Command
Set the number of times a packet can pass through a router. decnet [network-number] max-visits value

Adjust the Hello Timer  

Hosts use the hello messages to identify the hosts with which they can communicate directly. The Cisco IOS software sends hello messages every 15 seconds by default. On extremely slow serial lines, you might want to increase this value on a per-interface basis to reduce overhead.

To adjust the interval for sending hello messages, perform the following task in interface configuration mode:

Task Command
Adjust the interval (in seconds) for sending hello messages on interfaces with DECnet enabled. decnet hello-timer seconds

Disable Fast Switching

By default, our DECnet routing software implements fast switching of DECnet packets. You might want to disable fast switching to save memory space on interface cards and to help avoid congestion when high-bandwidth interfaces are writing large amounts of information to low-bandwidth interfaces. This is especially important when using rates slower than T1.

To disable fast switching of DECnet packets, perform the following task in interface configuration mode:

Task Command
Disable fast switching of DECnet packets on a per-interface basis. no decnet route-cache

Set the Congestion Threshold

If a router configured for DECnet experiences congestion, it sets the congestion-experienced bit. You can define the congestion threshold on a per-interface basis. By setting this threshold, you will cause the system to set the congestion-experienced bit if the output queue has more than the specified number of packets in it.

To set the congestion threshold, perform the following task in interface configuration mode:

Task Command
Set the congestion threshold. decnet congestion-threshold number

Adjust the Broadcast Routing Timer  

Other routers use broadcast updates to construct local routing tables. Increasing the time between routing updates on a per-interface basis reduces the amount of unnecessary network traffic. Digital calls this parameter the broadcast routing timer because Digital uses a different timer for serial lines. Our DECnet implementation does not make this distinction.

To adjust the broadcast routing timer, perform the following task in interface configuration mode:

Task Command
Adjust how often the Cisco IOS software sends routing updates that list all the hosts that the router can reach on a per-interface basis. decnet routing-timer seconds

Configure DECnet over DDR

Dial-on-demand routing (DDR) is now supported for DECnet. Refer to the "Configuring DDR" chapter in Wide-Area Networking Configuration Guide.

Configure DECnet over WANs

You can configure DECnet over X.25, SMDS, and Frame Relay networks. To do this, configure the appropriate address mappings as described in the "Configuring X.25 and LAPB," "Configuring SMDS," and "Configuring Frame Relay" chapters in the Wide-Area Networking Configuration Guide.

Enable Split Horizon

When split horizon is enabled, routing updates sent out on an interface do not include any information that was originally learned from that interface, and broadcasts are not retransmitted on the receiving interface. Disabling split horizon causes the Cisco IOS software to include all information in routing updates, and to resend broadcast packets on the network from which they were received.

To disable split horizon, perform the following task in interface configuration mode:

Task Command
Disable split horizon when sending routing updates. no decnet split-horizon

Monitor and Maintain the DECnet Network

To clear counters, test network node reachability, and display information about DECnet networks, perform the following tasks in EXEC mode:

Task Command
Clear the DECnet counters. clear decnet counters
Test network node reachability. ping decnet {host | address}
Display the global DECnet parameters. show decnet
Display the global DECnet status and configuration for all interfaces, or the status and configuration for a specified interface, including address, paths, cost, access lists, and more. show decnet interface [type number]
List address mapping information used by the DECnet ATG. show decnet map
Display all Phase IV and Phase IV Prime neighbors and the MAC address associated with each neighbor. show decnet neighbors
Display DECnet routing table. show decnet route [decnet-address]
Display static DECnet routing table. show decnet static
List DECnet traffic statistics, including datagrams sent, received, and forwarded. show decnet traffic

DECnet Configuration Examples

The following sections provide examples that show some common DECnet configuration activities:

DECnet Phase IV Prime Examples

This section includes examples of configuring DECnet Phase IV Prime support for inherent MAC addresses. The comments in these examples point out some possible configuration errors, in addition to explaining correct command lines.

In the following example, Ethernet interface 0 is configured for DECnet Phase IV Prime:

decnet routing iv-prime 1.1
interface ethernet 0
decnet cost 10
! Interface Ethernet 0 will have aa-00-04-00 form of MAC address. Router is 
! bilingual on interface Ethernet 0.

In the following example, Token Ring interface 1 is configured with a MAC address that is not supported by DECnet Phase IV:

decnet routing 2.1	
interface tokenring 1
decnet cost 5
mac-address 0000.0c00.62e6 
! Interface Token Ring 1 has MAC address as set 
! This is an error because the token ring interface has a MAC address that is 
! not Phase IV-compatible, and the router is not running Phase IV Prime.

In the following example, the router is not configured to support DECnet Phase IV Prime until later in the configuration:

interface tokenring 1
decnet cost 5
mac-address 0000.0c00.62e6 
! invalid configuration, since router is only Phase IV.
decnet routing iv-prime 5.5
! Become a Phase IV Prime router
interface tokenring 1
mac-address 0000.0c00.62e6 
! Valid configuration since the router is now running Phase IV Prime.

The following example shows valid and invalid ways of using the decnet multicast-map command:

decnet routing iv-prime 3.4
interface tokenring 1
decnet multicast-map phiv-prime-all-bridges c000.2000.0000 
! Invalid value (phiv-prime-all-bridges) for multicast ID string
interface tokenring 1
decnet multicast-map iv-prime-all-routers d000.2000.0000 
! Invalid value (d000.2000.0000) for functional address
interface tokenring 1
decnet multicast-map iv-prime-all-routers c000.2000.0000 
! This will work. The command redefines the multicast to functional address
! mapping for the "all Phase IV Prime routers" multicast.

DECnet Example

The following example illustrates the commands required for enabling DECnet. DECnet routing is established on a router at address 4.27. The node is configured as a Level 2, or interarea router. A cost of four is set for the Ethernet 0 interface. A cost of ten is set for the serial 1 interface.

decnet routing 4.27
decnet node area
interface ethernet 0
decnet cost 4
interface serial 1
decnet cost 10

Address Translation Example

In Figure 11, the router is connected to two DECnet networks using Ethernet. The following example illustrates how to configure an ATG between Network 0 and Network 1.


Figure 11: ATG Configuration Example


In Network 0, the router is configured at address 19.4 and is a Level 1 router. In Network 1, the router is configured at address 50.5 and is an area router. At this point, no routing information is exchanged between the two networks. Each network in the router has a separate routing table.

decnet 0 routing 19.4
decnet 0 node routing-iv
interface ethernet 0
decnet 0 cost 1
!
decnet 1 routing 50.5
decnet 1 node area
interface ethernet 1
decnet 1 cost 1

To establish a translation map, enter these commands:

decnet 0 map 19.5 1 50.1
decnet 1 map 47.1 0 19.1

Packets in Network 0 sent to virtual address 19.5 will be routed to Network 1, and the destination address will be translated to 50.1. Packets sent to virtual address 47.1 in Network 1 will be routed to Network 0 as 19.1.

Table 1 defines the parameters for the translation map.


Table  1: Packet Exchange between Nodes A and D
Source Destination
A packet addressed as: 19.1 19.5 is received on Ethernet 0 as 19.5
Translates to: 47.1 50.1 and is transmitted out Ethernet 1 as 50.1
A reply packet: 50.1 47.1 is received on Ethernet 1
Translates to: 19.5 19.1 and is transmitted on Ethernet 0

Network 0 uses a block of addresses from its area to map the remote nodes. In Network 0, the router will advertise nodes 19.5 and 19.6. These nodes must not already exist in Network 0.

Network 1 uses another area for the address translation. Since the Cisco IOS software will be advertising the availability of area 47, that area should not already exist in Network 1, because DECnet area fragmentation could occur.

Only nodes that exist in the maps on both networks will be able to communicate directly. Network 0 node 19.1 will be able to communicate with Network 1 node 50.1 (as 19.5), but will not be able to communicate directly with Network 1 node 60.1.

When naming nodes, use the appropriate address in each network. See the lists that follow for examples.

Network 0 VMS NCP Command File Sample
$MCR NCP
define node 19.1 name A
define node 19.2 name B
define node 19.3 name C
define node 19.4 name GS
define node 19.5 name D
define node 19.6 name F
Network 1 VMS NCP Command File Sample
$MCR NCP
define node 50.1 name D
define node 50.5 name GS
define node 60.1 name E
define node 19.1 name F
define node 47.1 name A
define node 47.2 name C

Phase IV-to-Phase V Conversion Example

Figure 12 shows that for the DECnet Phase IV-to-Phase V conversion to work properly, CLNS IS-IS must be configured on certain interfaces.

Note that although Router A has only Phase IV hosts connected by its Ethernet 0 interface, the interface must be configured for CLNS IS-IS for Router A to convert the Phase IV adjacency information into Phase V. If the Ethernet interface 0 on Router A is not configured for CLNS IS-IS, Router B will never get information about Router D and endnode 1.


Figure 12: Sample Phase IV-to-Phase V Network Conversion


Configuration for Router A
decnet routing 1.1
decnet conversion 49
clns routing
router isis
net 49.0001.aa00.0400.0104.00
interface ethernet 0
clns router isis
decnet cost 4
interface s 0
clns router isis
Sample Configuration for Router D
decnet routing 1.10
interface ethernet 0
decnet cost 4

Phase IV Areas through an OSI Backbone Example

The following example illustrates how to configure border routers to propagate Phase IV areas through an OSI backbone using the advertise feature. In this example, Router X in area 8 wants to communicate with Router Y in area 9. Figure 13 illustrates the network, and the configurations that follow illustrate the commands required for enabling the advertise feature.


Figure 13: Sample Phase IV/Phase V Backbone Network


Configuration for Router B
decnet conversion 49
!Propagate Area 9 reachability information
decnet advertise 9 4 2
!Create dummy OSI route to force conversion to Phase IV
clns route 49.0008 discard
Configuration for Router C
decnet conversion 49
!Propagate Area 8 reachability information
decnet advertise 8 6 3
!Create dummy OSI route to force conversion to Phase IV
clns route 49.0009 discard

The routing table for Router A will then contain the following, as displayed with the show decnet route EXEC command:

  Area       Cost  Hops   Next Hop to Node       Expires  Prio
*1             0     0     (Local) -> 1.1
*8             4     1   Ethernet1 -> 8.1           35     64    A
*9             5     2   Ethernet0 -> 1.2
  Node       Cost  Hops   Next Hop to Node       Expires  Prio
*(Area)        0     0     (Local) -> 1.1
*1.1           0     0     (Local) -> 1.1
*1.2           4     1   Ethernet4 -> 1.2           38     64    VA

The routing table for Router B will then contain the following:

  Area       Cost  Hops   Next Hop to Node       Expires  Prio
*1             0     0     (Local) -> 1.2
*8             8     2   Ethernet0 -> 1.1
*9             4     2       (OSI) -> 1.2
  Node       Cost  Hops   Next Hop to Node       Expires  Prio
*(Area)        0     0     (Local) -> 1.2
*1.1           4     1   Ethernet0 -> 1.1           37     64    VA
*1.2           0     0     (Local) -> 1.2

The routing table for Router C will then contain the following:

  Area       Cost  Hops   Next Hop to Node       Expires  Prio
*2             0     0     (Local) -> 2.1
*8             6     3       (OSI) -> 2.1
*9             8     2   Ethernet0 -> 2.2
  Node       Cost  Hops   Next Hop to Node       Expires  Prio
*(Area)        0     0     (Local) -> 2.1
*2.1           0     0     (Local) -> 2.1
*2.2           4     1   Ethernet0 -> 2.2           33     64    VA


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