Lucent Technologies 6000 - Manual (Page 367)

Configuring IP Routing
Introduction to IP routing on the MAX
MAX 6000/3000 Network Configuration Guide 9-3
The broadcast address of any subnet has the host portion of the IP address set to all ones. The
network address (or base address) represents the network itself, because the host portion of the
IP address is all zeros. For example, if the MAX assigns the following address to a remote
router:
IP address=198.5.248.120/29
The Ethernet attached to that router has the following address range:
198.5.248.120 — 198.5.248.127
in which 198.5.248.120 is a network (base) address and 198.5.248.127 is a broadcast
address.
A host route is a special-case IP address with a subnet mask of /32. Host routes are required for
dial-in hosts. For example:
198.5.248.40/32
Table 9-2 shows standard subnet masks for a class C network and the subnet notation.
Zero subnetworks
Early implementations of TCP/IP do not allow zero subnets, that is, subnetwork addresses in
which the last octet is zero. As a result, in early TCP/IP implementation, subnetworks are not
permitted to have the same base address that a class A, B, or C network would have. Lucent’s
implementation of RIP 2 and OSPF, like other modern implementations of TCP/IP, treat zero
subnetworks as they would any other network.
You should decide whether to support and configure zero subnetworks for your environment.
If you configure them in some cases and treat them as unsupported in other cases, you will
encounter routing problems.
Table 9-2. Standard subnet masks and Lucent notation
Subnet mask Number of host addresses Subnet notation
255.255.255.0 254 hosts + 1 broadcast, 1 network (base) /24
255.255.255.128 126 hosts + 1 broadcast, 1 network (base) /25
255.255.255.192 62 hosts + 1 broadcast, 1 network (base) /26
255.255.255.224 30 hosts + 1 broadcast, 1 network (base) /27
255.255.255.240 14 hosts + 1 broadcast, 1 network (base) /28
255.255.255.248 6 hosts + 1 broadcast, 1 network (base) /29
255.255.255.252 2 hosts + 1 broadcast, 1 network (base) /30
255.255.255.254 invalid subnet mask (no hosts) /31
255.255.255.255 1 host—a host route /32