IPX Routers and the Internal Network Number

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To facilitate optimal communication to services running on IPX routers advertising themselves using Novell NetWare Service Advertising Protocol (SAP), IPX routers that are hosting services, such as Novell NetWare servers or Windows 2000 Server–based computers, require the configuration of an IPX internal network number. The IPX internal network is a virtual network inside the router. Attached to this virtual network is a virtual network interface card with the MAC address of 0x00-00-00-00-00-01. The IPX internal network is announced using RIP for IPX just as physical IPX networks are. When services running on the router are advertised with SAP, they are advertised with the IPX internetwork address of the internal network number and the virtual MAC address.

The IPX internal network allows for the optimal routing of packets to services running on the IPX router. The following analysis of the IPX traffic before and after the use of the IPX internal network clearly illustrate this optimization.

IPX Traffic Before the IPX Internal Network

Figure 5.10 depicts a simple IPX internetwork and a file server process where the IPX internal network is not being used.

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Figure 5.10 Prior to Defining an IPX Internal Network Number

  1. The NetWare file server process running on IPX Router 1 advertises its location (using SAP) at the server address of AAAAAAAA:001111111111:0451 (IPX network:IPX Node:IPX Socket).

  2. The Host resolves the file server address by querying its default NetWare server (not shown in Figure 5.10).

  3. The Host broadcasts a RIP GetLocalTarget request on network BBBBBBBB requesting the best route to IPX network AAAAAAAA.

  4. IPX Router 1 responds with a route that is one hop and two ticks away.

  5. IPX Router 2 responds with a route that is one hop and two ticks away.

  6. The Host chooses IPX Router 2's response (either because it was the first response received or through a random selection of multiple routers with the lowest tick count).

  7. The Host sends a connection request packet to the file server process at AAAAAAAA:001111111111:0451 by forwarding it to IPX Router 2 at the MAC address of 00-44-44-44-44-44 on network BBBBBBBB.

  8. IPX Router 2 forwards the connection request packet to Router 1 at its MAC address 00-11-11-11-11-11 on network AAAAAAAA.

  9. The file server process on Router 1 responds to the connection request packet by forwarding it to the Host's MAC address (not shown in the figure) on network BBBBBBBB.

The end result of the RIP GetLocalTarget request sent by the Host is that packets sent from the Host to the file server process take a route that is not optimal. They are forwarded to IPX Router 2 when the optimal route is to IPX Router 1.

IPX Traffic After the IPX Internal Network

Figure 5.11 depicts the same simple IPX internetwork and file server process where the IPX internal network is being used.

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Figure 5.11 After Defining an IPX Internal Network Number

  1. The NetWare file server process running on IPX Router 1 advertises its location (using SAP) on the internal network at the server address of CCCCCCCC:000000000001:0451 (IPX network:IPX Node:IPX Socket).

  2. The Host resolves the file server address by querying its default NetWare server (not shown in Figure 5.11).

  3. The Host broadcasts a RIP GetLocalTarget packet on network BBBBBBBB requesting the best route to IPX network CCCCCCCC.

  4. IPX Router 1 responds with a route that is one hop and two ticks away.

  5. IPX Router 2 responds with a route that is two hops and three ticks away.

  6. The Host always chooses IPX Router 1's response because Router 1's route to network CCCCCCCC has the lowest tick count.

  7. The Host sends a connection request packet to the file server process at CCCCCCCC:00000000001:0451 by forwarding it to IPX Router 1 at the MAC address of 00-22-22-22-22-22 on network BBBBBBBB.

  8. The file server process on Router 1 responds to the connection request packet by forwarding it to the Host's MAC address (not shown in the figure) on network BBBBBBBB.

The end result of the RIP GetLocalTarget request by the Host is that packets sent from the Host to the file server process always take the optimal route.

Windows 2000 Router and the IPX Internal Network and Internal Adapter

A Windows 2000 Router supporting IPX routing can be configured with a unique IPX internal network number that is entered in the properties of the IPX/SPX/NetBIOS Compatible Transport. If the internal IPX network number is not configured, a unique IPX network number is automatically configured during the startup of the Windows 2000 Router.

The Windows 2000 Router automatic configuration process picks a random IPX network number and sends out a RIP GetLocalTarget packet requesting a route to the chosen IPX network number. If a RIP response is received, the chosen IPX network number cannot be used, and a new random IPX network number is chosen. If a RIP response is not received, the chosen IPX network number is automatically entered in the properties of the IPX/SPX/NetBIOS Compatible Transport.

To see the virtual network adapter corresponding to the IPX internal network, in the Routing and Remote Access snap-in, open your server, then IPX Routing , then General . The Internal interface appears in the details pane as an IPX routing interface and is the virtual network adapter for the IPX internal network of the server (see Figure 5.12).

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Figure 5.12 IPX Internal Adapter