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Configuring IPX Type 20 Packet Forwarding

Many applications in the NetWare environment use the Network Basic Input/Output System (NetBIOS) request services from IPX servers. These services include session establishment and termination and information transfer.

On a NetWare client, a NetBIOS application using IPX broadcasts type 20 propagation packets to all IPX networks to get information about named nodes on the network. NetBIOS uses named nodes for resources on the network. To communicate with these resources, NetWare clients need to map these named nodes to IPX addresses.

NetBIOS uses an IPX mechanism to map named nodes to IPX address. As you have seen throughout this book, Cisco routers block all network layer broadcast packets by default, including IPX type 20 propagation packets. If a router does not forward any type 20 propagation packets, and a NetWare client with an application using NetBIOS needs to traverse the router to obtain information about a named node on the network, the NetWare client is not capable of communicating with the server.

The IOS interface subcommand ipx type-20-propagation instructs the router to accept and forward type 20 propagation packets to other IPX interfaces that also have this subcom-mand configured. The IOS attempts to forward the IPX type 20 propagation packets in an intelligent manner ”such as by not putting the packets on interfaces that route to the original source interface.

Instead of forwarding IPX type 20 propagation packets to multiple network segments, you can forward these packets to a specific IPX network address, thereby potentially reducing the number of broadcast packets sent throughout your IPX network. The IOS global configuration command ipx type-20-helpered enables the forwarding of IPX type 20 packets to a specific IPX address. The IOS interface subcommand ipx helper-address specifies the IPX address to forward type 20 packets to. The ipx type-20-helpered and the ipx type-20-propagation commands are mutually exclusive. The IOS must either forward type 20 propagation packets to other similarly configured interfaces or forward type 20 packets to an IPX address.

In the following configuration on the ZIP network, we forward all IPX type 20 packets on the Singapore router, via interface Ethernet 0, to a specific IPX server in San Francisco at IPX address aa.0005.0112.0474:

Singapore#

configure

Configuring from terminal, memory, or network [terminal]?

Enter configuration commands, one per line.  End with CTRL+Z.

Singapore(config)#

ipx type-20-helpered

Singapore(config)#

interface ethernet 0

Singapore(config-if)#

ipx helper-address aa.0005.0112.0474

Singapore(config-if)#

^Z

Summary

We have covered the basics of the IPX protocol suite, the core commands for bringing up an IPX network, and some of the additional commands often implemented on large IPX networks. By no means will this chapter make you an expert in IPX networks, but it will get you up and running. Following are the central concepts of the chapter:

An IPX address takes the form network.node , in which network is a 32-bit number designating a LAN or WAN segment and node is a 48-bit number designating a client or server. The network portion is assigned by the network administrator. The node portion is often the same as the 48-bit data link layer address for the device.
For NetWare clients , NetWare servers, and Cisco routers to communicate properly on an IPX LAN segment, they must be running the same IPX encapsulation. Although in some situations you can choose from among multiple encapsulation methods , most often the version of NetWare dictates which one must be used.
Like IP routing, IPX routing can be configured manually or via dynamic routing protocols. RIP, NLSP, and EIGRP are dynamic routing protocols for IPX. IPX RIP is enabled on all IPX interfaces by default when you use the global configuration command ipx routing .
SAP is a dynamic services protocol that advertises what services are available on an IPX network. It is configured by default on all IPX-configured interfaces. SAP filters can be used to limit the amount of SAP traffic sent and received by a router.
To enable NetBIOS broadcasts to be received and sent by a Cisco router, you must use the ipx type-20-propagation or ipx type-20-helpered command.
A variety of show, debug, and ping commands are available for verifying configurations and for troubleshooting your IPX network. In addition to those summarized in the Table 6-4, see Table 6-5 for a review of pertinent commands.

Table 6-4. Summary of EXEC Commands for Configuring IPX

Command	Description
clear ipx route	Clears the entire IPX routing table or, if specified, a particular route.
ping network.node	Tests the indicated IPX address to determine whether it is reachable and responsive .
ping ipx network.node	In privileged mode, used to send either Cisco Echoes or Novell Standard Echoes to the indicated IPX address to determine whether it is reachable and responsive.
show ipx access-lists	Shows all IPX access lists defined on the router.
show ipx interface brief	Shows a brief summary of IPX network information and interface statuses for all available interfaces on the device.
show ipx interface interface	Shows all the parameters associated with the IPX configuration of an interface.
show ipx route	Outputs the IPX routing table of the router.
show ipx route network.node	Shows IPX routing information for the specified route.
show ipx servers	Shows a list of all the currently known IPX servers.
show ipx traffic	Outputs overall statistics about the operation of IPX on the router.

Table 6-5. Summary of Configuration Commands for IPX Networks

Command	Description
access-list	Creates a numbered access list and its associated filtering criteria.
area-address address mask	Defines the area address prefix and mask for NLSP.
dialer map ipx	Statically maps an IPX address to system names and phone numbers for ISDN calls.
frame-relay map ipx	Maps an IPX address to a Frame Relay DLCI.
ipx access- group list [in out]	Applies the indicated access list to the task of filtering incoming or outgoing packets on an interface.
ipx access-list {extended sap standard} name	Assigns a named IPX access and its associated filtering criteria.
ipx gns-round- robin	Stipulates a round-robin selection method for choosing among multiple eligible servers when the router responds to GNS requests .
ipx input-sap-filter list	Interface subcommand that instructs the router to filter inbound SAP packets based on specific access list criteria.
ipx internal-network network	Defines an internal network number on the router for NLSP.
ipx maximum paths number	Configures the router to permit the specified number of equal- cost paths in its IPX routing table.
ipx network network [encapsulation secondary]	Defines the IPX network for that interface. Optionally, defines the encapsulation method (for example, snap and arpa ) used on that interface and whether or not the network is primary or secondary on the interface.
ipx output-gns-filter list	Interface subcommand that instructs the router to filter outbound GNS packets from routers based on specific access list criteria.
ipx output-sap-filter list	Interface subcommand that instructs the router to filter outbound SAP packets based on specific access list criteria.
ipx ppp-client loopback	Interface subcommand that assigns the IPX number of a loopback interface for use by IPX PPP clients.
ipx route	Configures a static IPX route.
ipx router eigrp autonomous-system	Enables EIGRP as a routing process for IPX.
ipx router nlsp tag	Enables the specified NLSP process as a routing process for IPX.
ipx router-sap-filter	Applies a filter to all SAP advertisements based on specific access list criteria.
ipx routing	Enables IPX routing on the router.
ipx sap	Defines static SAP table entries.
ipx sap-incremental-eigrp	Configures a router to send SAP messages only when a change occurs in the SAP table.
ipx update interval {rip sap} seconds	Interface subcommand that changes the IPX RIP or SAP interval to the number of seconds specified.
map group	Assigns a named map group to an interface for use in mapping IPX addresses to ATM data-link addresses on an interface.
map list	Creates a named map list to configure the mapping of IPX addresses to PVCs or SVCs in ATM addressing.
network network	Associates an IPX network number with EIGRP.
x25 map ipx	Statically maps an IPX address to an X.121 address.

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