Subnet Addresses And Masks - Novell NETWARE 6-DOCUMENTATION Manual

Subnet Addresses and Masks

Figure 10 A 4-byte IP address
<Network Address>
Network Address
Communication between a node on a local subnet and a node on a different
subnet is similar to communication between nodes on two different networks.
To a user, routing between subnets is transparent. Internally, the IP software
recognizes any IP addresses that are destined for a remote subnet and sends
those packets to the router on that subnet.
As in network-to-network communication, the routing information for
communication between subnets is maintained in the routing table (by IP).
When a network is divided into subnets, the host address portion of the IP
address is divided into two parts, just as the IP address itself is divided into
two parts. The host address portion specifies both the subnet of the IP network
and the node on that subnet.
The 4-byte IP address consists of a network address and a host portion, as
shown in Figure 10.
<Subnet Address> <Host Address>
Host Portion
For instance, if a network has the Class B IP network address portion 129.47,
the remainder of the IP address can be divided into subnet addresses and host
addresses. Controlled by the local network administrator, this division allows
the most flexibility for network development at the local site. For example, the
subnet address could comprise 4 bits of the remaining 2 bytes. This allows 15
subnets, each with 4,094 nodes. Or, in another case, the subnet address could
comprise 8 bits, allowing 255 subnets (a subnet address of all ones is not
valid), each with 254 nodes.
NOTE:
NetWare routing software supports the use of all zeros in the subnet field
(subnet zero). However, a subnet field with all ones denotes all subnets of a
particular network; therefore, a subnet field with all ones cannot be used as a local
IP address.
Figure 11 on page 30
router shown has physical attachments and IP addresses on both subnets
(129.47.128.1 and 129.47.192.1). It might also have physical devices and IP
addresses (nn.nn.nn.nn) connecting it to other networks.
shows a single IP network divided into two subnets. The
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Understanding