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This chapter describes the procedures for configuring your system to perform Xerox Network Systems (XNS) routing. It also describes how the router works and gives guidelines for operating, managing, and troubleshooting it.
For conceptual information, see "How the XNS Router Works" later in this chapter.
The procedure in this section describes the minimum steps required to enable your system to route XNS packets. Depending on your network requirements, you can use the default values of the parameters, or you can further configure the router according to later sections in this chapter.
The parameters in the IDP and RIPXNS Services enable XNS routing functions.
When setting up the basic XNS router, you first configure the router for LAN ports and Point-to Point Protocol (PPP) links.
Before beginning this procedure, complete the following tasks:
To set up the router for XNS routing, follow these steps:
1 . Enable XNS routing by entering:
SETDefault -IDP CONTrol = Route
2 . Configure XNS network numbers on each port connected (local interface or serial line interface) using:
SETDefault !<port> -IDP NETnumber = &<number>(0-FFFFFFFE)
3 . Verify the XNS configuration by entering:
SHow -IDP CONFiguration
4 . Begin routing table information exchanges with other routers that interface with a port using:
SETDefault !<port> -RIPXNS CONTrol = Enabled
5 . Repeat step 4 for each port being used for XNS routing.
For more information on dynamic and static routes, see "Customizing the XNS Router" later in this chapter.
XNS routing over Frame Relay, Asynchronous Transfer Mode data exchange interface (ATM DXI), and X.25 is supported over fully meshed, partially meshed, and nonmeshed topologies. If you plan to route XNS over a partially meshed or nonmeshed topology, you must create a virtual port for each remote network that is attached to a Frame Relay, ATM DXI, or X.25 cloud. For complete information on configuring XNS routing over Frame Relay, ATM DXI, or X.25, including a discussion of fully meshed, partially meshed, and nonmeshed topologies and virtual ports, see the Configuring Wide Area Networking Using Frame Relay chapter, the Configuring Wide Area Networking Using the ATM DXI chapter, and the Configuring Wide Area Networking Using X.25 chapter, respectively. For information on the number of virtual ports supported per platform, see Table 11 in the Configuring Advanced Ports and Paths chapter.
Routing XNS over Switched Multimegabit Data Service (SMDS) is supported over fully meshed and nonmeshed topologies (nonmeshed topologies require virtual ports). In addition, SMDS virtual ports are supported and can be used for traffic separation and various filtering of by assigning groups of nodes to different virtual ports. For more information, see the Configuring Wide Area Networking Using SMDS chapter.
To configure your XNS router to perform routing over PPP, see Chapter 43. For more information on wide area networking using Integrated Services Digital Network (ISDN), see the Configuring Wide Area Networking Using ISDN chapter.
After you have configured the basic XNS router, you should verify the configuration to see if you can reach other XNS hosts.
Before you use the router for interconnecting networks, verify the router configuration by following these steps:
1 . Check the router path configuration by entering:
SHow -PATH CONFiguration
2 . Check the router port configuration by entering:
SHow -PORT CONFiguration
3 . Examine the IDP Service configuration by entering:
SHow -IDP CONFiguration
4 . Examine the RIPXNS Service configuration by entering:
SHow -RIPXNS CONFiguration
5 . Check the state of all networks assigned to the ports of a router by entering:
SHow -IDP NETnumber
6 . Check the XNS Routing Table to see if all the networks are reachable by entering:
SHow -IDP AllRoutes Long
7 . Make a connection from a host on one attached network to a host on another network to see if packets can be routed across the router.
REMote &3141%080002001234
REMote &3142%08000200abcd
Figure 219 
Checking Connectivity between Routers
To display statistics for the IDP Service, enter:
SHow -SYS STATistics -IDP
To display statistics for the RIPXNS Service, enter:
SHow -SYS STATistics -RIPXNS
You can collect statistics for a specific time period by using the SampleTime and STATistics parameters. For more information on these parameters, see the SYS Service Parameters chapter in Reference for Enterprise OS Software. For information on interpreting the statistics displays, see the Statistics Displays appendix.
If you are unable to make connections to other networks after setting up the router, review the following troubleshooting procedure. This procedure can help correct problems in making single-hop (involving one router) and multiple-hop (involving more than one router) connections.
To troubleshoot the basic XNS router configuration, follow these steps:
1 . Check that all cables on all routers in a specific path in the routing table are properly connected and that the routers are properly installed.
2 . Check the -IDP NETnumber and the network status by entering:
SHow -IDP NETnumber
3 . Check the values of -RIPXNS CONTrol parameter by entering:
SHow -RIPXNS CONTrol
4 . Check whether the network you are trying to reach is in the XNS Routing Table by entering:
SHow -IDP AllRoutes
This section describes these router activities and explains how you can influence the router's routing decisions under different circumstances.
An XNS network is configured on each port where XNS packets are received and sent. Figure 220 is an example showing a wide area router connecting two local Ethernet networks (Santa Clara) to two wide area networks (Los Angeles and Santa Barbara).
Figure 220 
Wide Area Router Connecting Four XNS Networks
Any physically attached network, Ethernet or serial line, is considered a directly connected network or "local" network. If more than one serial line is assigned to one port, that port is considered a single directly connected XNS network.
A router must check its routing table to determine where to route a packet. If the destination is on an attached network, the router can send it directly to the network. But if the destination is not directly connected, the router must route the packet to another router (called a gateway) that is closer to the destination. The route to a remote network can be statically configured or dynamically learned through routing protocols, such as the Routing Information Protocol (RIP) for XNS.
The following sections describe the two types of routes (static and dynamic) and how to define them.
A static route is a user-defined route by which a remote network can be reached. To define a static route, enter the ADD -IDP ROUte command and specify the appropriate route information. For more information on setting the ROUte parameter, see the IDP Service Parameters chapter in Reference for Enterprise OS Software.
For example, on router 1 in Figure 220, you can add a static route for the Los Angeles network as follows:
ADD -IDP ROUte &1122 &2233%08000100abcc
To display the table of static routes, enter:
SHow -IDP ROUte
Once a static route is configured for a specific destination network, no dynamic routes will be added for that destination network.
You must configure the router with a network number (see "Displaying Routing Information" later in this chapter) before the router will accept static routes.
Dynamic routes are routes that are learned dynamically through RIP. RIP allows the periodic exchange of routing table information with other XNS routers. Gateways use this information to route packets to other networks. For more information on this protocol, see "Learning Routes" later in this chapter.
This section describes ways that you can enhance the performance of the XNS router.
You can change the way the router broadcasts update packets using parameters in the RIPXNS Service (see Table 64).
The RIPXNS parameters are automatically configured to their default values when you configure the -IDP CONTrol parameter for routing. In some cases, however, you may want to change the default configuration.
To modify the RIPXNS parameters, see the following parameter descriptions:
The -RIPXNS CONTrol parameter determines on a per-port basis how the router sends the routing table information to the network. The following are the default values for the RIPXNS parameters:
CONTrol = (Enabled, Trigger, NoPoison, NewNbrMap, GlobBcast)
The impact of setting the -RIPXNS CONTrol parameter to Enabled depends on the setting of the -IDP CONTrol parameter. Table 65 shows the relationship of the -IDP CONTrol parameter to the -RIPXNS CONTrol parameter.
Setting the -RIPXNS CONTrol parameter to Trigger causes the router to send an update packet when the network topology changes. The advantage is that triggered updates immediately allow the network to know a potentially better route to a particular network. Setting the -RIPXNS CONTrol parameter to NoTrigger reduces the amount of data packets broadcast over the network, and normal update packets are sent only at the time interval specified by the UpdateTime parameter.
Setting the -RIPXNS CONTrol parameter to Poison causes the router to set the number of hops for a specific table entry to 16 when it sends routing table updates. It does this to prevent routing loops in which two gateways are trying continually to update each other with the same information. The poisoned information (specified by a hop count of 16) remains in the router's update packet, adding to the data traffic on the network.
Setting the -RIPXNS CONTrol parameter to NoPoison prevents the router from sending poisoned routing information in an update packet, thus reducing the amount of data traffic over the network.
The -RIPXNS UpdateTime parameter specifies the time interval by which the router sends its routing table updates. For networks that seldom experience topology changes, the interval time can be set higher than the default value to reduce the amount of network traffic. For networks that often experience topology changes, this value can be set lower than the default value.
The lower you set the UpdateTime value, the more data traffic is generated on the network. Increased traffic can degrade network performance.
In addition to routing configuration changes available through the RIPXNS Service parameters, you can configure the -IDP CONTrol parameter to provide error checking through the Checksum | NoChecksum value. Checksum provides a high degree of reliability in detecting bad data sent over the network. If Checksum is enabled, a router verifies the IDP checksum of a packet before it forwards the packet. The cost of this service, however, is lower network performance. The default value is NoChecksum.
To configure the router to provide error checking, enter:
SETDefault -IDP CONTrol = Checksum
This section provides general information about XNS routing.
Normally, every 30 seconds (by default) or every time it learns a route change for a network, the router uses broadcast packets to report to its neighbors the following types of information:
You can configure some router parameters to determine how the router sends out the updates by completing the following tasks:
The routing table provides information that determines how a packet is routed. The long form of the routing table displays only the most efficient route.
To display the long form, enter:
SHow -IDP AllRoutes Long
The following is a typical example of the long form of the routing table:
Asterisks in the display indicate static routes.
Depending on the AllRoutes option selected, the routing table can include the following information, which determines how a packet is routed:
This is the port associated with the attached network.
The router maintains valid routes to remote networks. A network route is used to reach all hosts on the network. If you have a large routing table, you can specify a network number to verify its reachability by using the SHow -IDP AllRoutes <NETnumber> syntax.
This is the XNS address of the gateway to which a router must send the packet before the packet can be routed to the destination. For more information on gateway addresses, see "Static Routes" earlier in this chapter.
The numbers of hops is equal to the number of gateways traversed. The XNS router selects the most efficient path for information. The most efficient path is the path that requires the fewest hops to reach a destination. In cases where two paths require the same number of hops, the router selects the first entry in the routing table.
For each destination address, the router can support up to two routes (that is, two gateways). These routes, either learned or configured, are stored in the routing table. The router selects the most efficient route to reach a destination. For information on how the router makes routing decisions, see "Learning Routes" earlier in this chapter.
To display the short form of the routing table, enter:
SHow -IDP AllRoutes
The short form, which is the default, only displays network numbers and hop counts.
Routes in the routing table are deleted differently depending on whether they are static or dynamic routes:
For example, to delete the Ethernet static route configured in "Static Routes" earlier in this chapter, enter:
DELete -IDP ROUte &1122
For example, if the UpdateTime parameter is set to 30 seconds, the route is deleted if no RIP updates are received for the route within 90 seconds.
To remove all dynamic routes, enter:
FLush -IDP AllRoutes
The types of networks that are considered reachable when a router broadcasts its RIP update packets are as follows:
Some networks, though accessible, are not reported by the router. For example, in Figure 221, router B broadcasts an update packet on network &2222. The packet does not include network &1111, because this network is learned from the same port on which the packet is broadcast. This process is known as split horizon.
Split horizon prevents routing loops caused by including routes in the updates sent to the port from which the routes were originally learned.
When no poison reverse is used, the router omits this type of route from routing updates sent to the same port.
With poison reverse, the router includes this type of route in its report, but the number of hops associated with that network is 16. For example, with poison reverse, router A includes networks &1111 and &3333 in its report sent to router B, but specifies that the number of hops for network &3333 is 16, while the number of hops for network &1111 is 1. Because RIP considers any network with a hop number higher than 15 unreachable, router B, upon receipt of the report, knows that packets destined for network &3333 should never be routed to router A. Through this same process, router A will know network &1111 is unreachable through router B.
Split horizon guarantees that if router B's connection with network &3333 fails, it will not send packets to router A, under the assumption that router A can reach the destination network (&3333), because it cannot.
Figure 221 XNS Routing Using Split Horizon
