Information Technology Reference
In-Depth Information
Each /30 subnetwork includes the subnetwork number, two IP addresses, and a broadcast
address. Table 8-23 shows the bits for 130.20.78.8/30.
Ta b l e 8 - 2 3
Addresses Within Subnetwork 110.20.78.8/30
Binary Address
IP Address
Function
10000010 00010100 01001110 000010
00
130.20.78.8
Subnetwork
10000010 00010100 01001110 000010
01
130.20.78.9
IP address 1
10000010 00010100 01001110 000010
10
130.20.78.10
IP address 2
10000010 00010100 01001110 000010
11
130.20.78.11
Broadcast address
Loopback Addresses
Yo u c a n a l s o r e s e r v e a s u b n e t fo r r o u t e r l o o p b a c k a d d r e s s e s . L o o p b a c k a d d r e s s e s p r o v i d e
an always-up interface to use for router-management connectivity. The loopback address
can also serve as the router ID for some routing protocols. The loopback address is a sin-
gle IP address with a 32-bit mask. In the previous example, network 130.20.75.0/24 could
provide 255 loopback addresses for network devices, starting with 130.20.75.1/32 and
ending with 130.20.75.255/32.
IP Telephony Networks
Yo u s h o u l d r e s e r v e s e p a r a t e s u b n e t s fo r L A N s u s i n g I P p h o n e s . I P p h o n e s a r e n o r m a l l y
placed in a VLAN that is in a logical segment separate from that of the user workstations.
Separating voice and data on different subnets or VLANs also aids in providing QoS for
voice traffic with regard to classifying, queuing, and buffering. This design rule also facili-
tates troubleshooting.
Ta ble 8 - 2 4 shows an example of allocating IP addresses for a small network for a company
located within three buildings. Notice that separate VLANs are used for the VoIP devices.
Ta b l e 8 - 2 4
IP Address Allocation for VoIP Networks
Building Floor/Function
VLAN Number
IP Subnet
First-floor data
VLAN 11
172.16.11.0/24
Second-floor data
VLAN 12
172.16.12.0/24
Third-floor data
VLAN 13
172.16.13.0/24
First-floor VoIP
VLAN 111
172.16.111.0/24
Second-floor VoIP
VLAN 112
172.16.112.0/24
Third-floor VoIP
VLAN 113
