OSI/AS and OSI/TS Supplement (Includes RFC-1006 Support)

Introduction to the Tandem TCP/IP Subsystem
Introduction to RFC-1006
1–10 107751 Tandem Computers Incorporated
Figure 1-7. Hosts and a Gateway in an Internetwork
095
HOST4
98.0.1.6
37.0.4.1
Network NETA
Internet Address
= 98.0.0.0
HOST3
98.0.7.4
Network NETB
Internet Address
= 37.0.0.0
HOST7
37.0.3.9
HOST8
37.0.3.2
HOST6
37.0.8.1
HOST2
98.0.3.1
HOST11
37.2.2.9
HOST10
37.1.3.5
HOST9
37.1.0.8
HOST12
37.2.8.1
HOST1
98.0.2.9
Gateway
As described in RFC 950, each network can be divided into a number of subnetworks,
or subnets. Within a network, each subnet is treated as a separate network; outside
the network, the subnets appear as part of a single network. Each subnet attached to a
host is reached through a device (or a pseudodevice, such as a loopback driver) that
provides an interface for the Internet Protocol (IP) datagram transmission. In this
manual, the term subnet is also used to refer to the interface through which the subnet
is reached.
The addressing of subnets within a LAN is accomplished by dividing the local address
portion of the Internet address into a subnet number and a host number. The subnet
number identifies the specific subnet, and the host number identifies the host system
within the subnet. Figure 1-8 shows an example of the same network as shown in
Figure 1-7, but with subnets added. In Figure 1-8, NETB consists of subnets NETC and
NETD.
To identify the portion of the Internet address that represents the subnet number, a 32-
bit subnet mask is used. In the mask, all bits corresponding to the network address
and its subnet address are set to 1, and all bits corresponding to the host within the
subnet are set to 0.