User`s guide

8-2 Preliminary November 23, 1998 MultiVoice Gateway for the MAX— User’s Guide
Configuring IP Routing
Introduction to IP routing and interfaces
For example, a class C address such as 198.5.248.40 has 24 network bits, so its default mask is
24. The 24 network bits leave 8 bits for the host portion of the address. So one class C network
can support up to 253 hosts.
Figure 8-1. A class C IP address
As shown in Table 8-1, a mask has a binary 1 in each masked position. Therefore, the default,
24-bit, subnet mask for a class C address can be represented in dotted decimal notation as
255.255.255.0.
For specifying a different subnet mask, the MultiVoice Gateway supports a modifier that
specifies the total number of network bits in the address. For example:
IP address = 198.5.248.40
Mask = 255.255.255.248
In this example, the mask specification indicates that 29 bits of the address specify the
network. This is commonly referred to as a 29-bit subnet. The three remaining bits specify
unique hosts.
Figure 8-2. A 29-bit subnet mask and number of supported hosts
Three available bits allow eight possible bit combinations. Of the eight possible host addresses,
two are reserved, as follows:
000 — Reserved for the network (base address)
001
010
100
110
101
011
111 — Reserved for the broadcast address of the subnet
Ascend notation
When you display a MultiVoice Gateway routing table, entry, the subnet mask follows the IP
address, and a slash separates the two values. For example, if the address 198.5.248.40 has a
29-bit mask, it appears in the routing table as 198.5.248.40/29.
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0
Default 24 bits
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0
Default 24 bits
5-bit subnet Total network bits=29
255
128
64
32
16 8 4
2
Number of host addresses
(2 of which are reserved