Description of Segment

TABLE 2 . 5 Subnet Masks for Figure 2.2
Description of Segment
Number of IP
Addresses Required
Subnet Mask (Number
of Subnet Bits)
Server farm 300 255.255.254.0 (23)
Ethernet user segment 200 255.255.255.0 (24)
Serial link 2 255.255.255.252 (30)
Router interconnection
switched subnet
4 255.255.255.248 (29)
3. Starting with the segment requiring the greatest prefix length, begin allocating addresses.
Let’s begin with the serial link, which has a prefix length of 30 bits. Because all of our addresses
are going to start with 172.16, we will examine only the last 16 bits of the IP address. In Table 2.6,
we see the binary representations of the last two octets of the subnet mask, the subnet address, the
first and last valid IP addresses in the subnet, and the broadcast address. Remember that the host
portion of an assigned address cannot be all 1s, which is the broadcast address, or all 0s, which
is the address of the network, or wire.