Addressing and Routing are closely coupled. There are subnetting & supernetting need to be take in account.
IP addressing provides a logical counterpart to physical network address at link layer.
IP addr is logical in that addr may be changed easily to reflect changes in the logical structure of the network. This is a advantage of flexibility in Network Design.
It is like a trade-off within Addr Strategy in assigning addr space versus the complexity of interpreting.
IP uses an addr mask to show which bits in the addr are host and which are network.
The network prefix can be displayed in 3 formats:
-
bit-count, prefered use
-
decimal, old style
-
hexa, seems like 0x
$show ip route
output is decimal
R 192.168.1.0 255.255.255.0 [120/2] 192.168.4.1 S1
C 192.168.2.0 255.255.255.0 is directly connected. E0
$ip netmask-format hexadecimal
output is hexadecimal
R 192.168.1.0 0xFFFFF00 [120/2] 192.168.4.1 S1
C 192.168.2.0 0xFFFFF00 is directly connected. E0
$ip netmask-format bit-count
output is bit-format
| mask | Addr | Usage |
|---|---|---|
| 255.255.255.0 | 2e8-2 = 254 | too less |
| 255.255.0.0 | 2e16-2 = 65534 | often used |
| mask | IP Addr |
|---|---|
| 255.255.255.0 | 255.255.255.1 |
| 255.255.0.0 | 255.255.0.1 |
192.92.240.0 - 192.92.255.0
192.92.240.0/20
/
External Network ----- 192.92.240.0 -------- R -- 240.0 ~ 255.0
255.255.240.0 \
host
/
/
/
192.92.243.168
/
/
/
/
ISP ------- 192.92.243.92 ------host
R ----- R + hub ----- 192.92.240.16 ---- R ------- 192.92.243.32 ------ host
192.92.240.0 255.255.255.252 \ 255.255.255.224
255.255.240.0 | \
| \
192.92.240.20 \
| 192.92.243.64
R \
| \
192.92.245.x \
255.255.255.224 host
|
host