Installing and Administering LAN/9000 Software

126 Chapter6
Network Addressing
Networking Terminology
You must configure the initial interface for a card/encapsulation type
before you can configure subsequent interfaces for the same
card/encapsulation type. For example, you must configure lan0:0 (or
lan0) before you configure lan0:1 and lan0:2. Once you have configured
the initial interface, you can configure the subsequent interfaces in any
order. Note that the IP addresses assigned to a card may be on the same
subnet or on different subnets. See the section “Interfaces,” in Chapter 7
for more information about logical interfaces and interface names.
An initial interface cannot be removed from the system until all
subsequent logical interfaces are removed. You can remove subsequent
interfaces from the system with the ifconfig command, as in the
following example:
ifconfig lan1:1 inet 0.0.0.0
The initial interface (for example, lan1) can then be removed from the
system with the ifconfig command, as in the following example:
ifconfig lan1 unplumb
A loopback interface does not have a hardware device associated with it.
The name ofthis type of interface is lo0, denoting the loopback interface.
A loopback interface is automatically created by the TCP/IP stack even if
the system is not connected to a network.
Gateway
A gateway is a device used to connect two or more networks. The
gateway serves to route information among the networks. An HP 9000
with two or more LAN cards installed may act as a LAN-to-LAN
gateway. Such a node may also be referred to as a LAN-to-LAN router or
IP router. If a node is a gateway, it affects how you configure and
maintain LAN software. Refer to node D in the network maps in Figure
6-8 and Figure 6-14 for examples of gateways. A gateway system has to
have at least two network interfaces configured, one for each network to
which it belongs. A gateway can be either a router or a system.
Routing Table
Each node on the LAN has a routing table. A routing table contains
information about the route to nodes on other LANs. The connections to
other LANs are made through gateways.