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