Internetworks

Two or more networks of the same type or of different types can be linked together to form an internetwork or internet. For example, if you wanted to connect the nodes in a Point-to-Point network with the nodes on a LAN, the combination of the two networks would be called an internetwork. Creation of an internetwork allows any node on one network to communicate with any node on another network that is part of the same internetwork. Up to 256 individual networks can belong to the same NS internetwork.

The divisions between the networks in an internetwork are called network boundaries. Nodes in each network will have the same network address (network portion of the IP address); however, each network within the internetwork will have its own unique network address.

The networks in an internetwork may be connected by a bridge or router, or by HP 3000 Series 900 systems configured as gateways.

Gateways

One method of joining networks in an internetwork is by using gateways. An HP 3000 system can have up to 14 gateways (combined number of full gateways and gateway halves).

Full Gateways versus Gateway Halves

NS 3000/iX allows you to choose between connecting two networks with a full gateway or connecting them with two gateway halves. A full gateway is a node configured as a full member of two (or more) networks for the purpose of passing information between the networks to which it belongs. The node is considered a member of each of the networks for which it is configured.

A node that is a gateway half is configured as a member of a network and as a partner of another gateway half. A gateway half link that joins two networks connects two nodes (a gateway half pair) by a Point-to-Point link (NS Point-to-Point 3000/iX Network link). The gateway half link and pair is not considered a network itself. Each of the paired gateway halves is configured as a member of a different network (the two networks to be connected) and as a gateway half on the same gateway half link. Together, the two gateway halves function as a full gateway.

Gateway Configuration Overview

Gateway configuration includes both identifying neighbor gateways in each node's configuration file and configuring gateway half NIs for nodes that will serve as one half of a gateway half pair. These tasks are described as follows.

Identifying Neighbor Gateways

If you are including gateways in your internet configuration, you may want to modify each node's configuration file so that the node is aware of all of its neighbor gateways (gateways on the same link). You accomplish this during configuration of each network interface for which you want to allow communications over the gateway. You will find step-by-step instructions for identifying neighbor gateways in each of the link configuration sections of this manual.

An alternative to identifying neighbor gateways in every node's configuration file is to configure a default gateway for the node. Instructions for doing so are included in this manual.

The next pages show several examples of gateway configuration.

Neighbor Gateway Examples

When using NMMGR to configure any node, you will be entering the identities of all the neighbor gateways into the configuration of the node. The following examples illustrate several gateway configuration scenarios based on the network represented in Figure 2-3 “Gateway Configuration Scenarios”.

Example 1: The node you are configuring may be a non-gateway, such as node D in Figure 2-3 “Gateway Configuration Scenarios”. You would need to enter the identities of each of its neighbor gateways, in this case nodes C and E, at the Neighbor Gateways screen. On the Neighbor Gateway Reachable Networks screen, you would also enter the IP addresses of networks 1 and 3 as two of the configured reachable networks reachable through gateway node C.
Example 2: The node you are configuring may be a gateway half, such as node E in Figure 2-3 “Gateway Configuration Scenarios”. You will still need to enter the identities of the node's neighbor gateways as you configure the NI (in this case, node C is the neighbor gateway). You will also need to configure a gateway half NI for the node, as described under "Configuring a Gateway-Half Pair."
Example 3: The node you are configuring may be a full gateway, such as nodes B and C in Figure 2-3 “Gateway Configuration Scenarios”. Though full gateways are never actually identified as such in the configuration process, they too, must know about the other gateways. If you were configuring node C, you would identify nodes B and E and neighbor gateways.
Example 4: One of the gateways on your internetwork may be designated as a default gateway, such as node C in Figure 2-3 “Gateway Configuration Scenarios”. A default gateway is a gateway that is designated to receive any traffic for which the network is unable to identify a destination. You must identify the node as a default gateway in the configuration file of each node that will access it as the default gateway. If you were configuring node D, you would identify node C as a default gateway by entering an at sign (@) in one of the IP address fields of the Neighbor Gateway Reachable Networks screen. Only one gateway may be designated as a default gateway for each node. The default gateway must be on a LAN or Token Ring network.

Configuring a Gateway Half Pair

If you are configuring a gateway half pair, you will need to configure a gateway half NI for each half of the gateway pair. You will find step-by-step instructions for configuring a gateway half NI in this manual.

In Figure 2-3 “Gateway Configuration Scenarios”, nodes E and F form a gateway half pair. When you configure a node as a gateway half, you enter its partner's IP address into this gateway half's configuration in the Gatehalf Configuration screen. If you were to configure node E in the figure, you would enter the IP address of node F.

Figure 2-3 Gateway Configuration Scenarios

Gateway halves require the configuration of two separate network interfaces on each node: one for the gateway half, the other for the network it interfaces to (for example, a LAN or Point-to-Point NI). You will need to follow the instructions for the specific NI type, depending on the network type) and then follow the instructions to enter configuration items specific to the gateway half NI.

Worksheets that will aid you in planning for internetwork communication are located in Chapter 4 “Planning for Node Configuration”

Internetworks

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