Fundamentals
- an IPv4 address is 32 bits long
- written as 4 octests in dotted decimal format
- for example: 192.168.10.15
- each octet is 8 bits long: (4 x 8 = 32 )
# check ip on windows command prompt
ipconfig
# check ip on linux terminal
ifconfig
# get default gateway on linux terminal
ip route
# check ip in Cisco IOS
enable
ip interface brief # show ip address
show interface # more detailed with subnet mask etc.
Static vs. automatic addressing
- IP address usually
- set manually on servers, printers, and network devices
- assigned automatically on desktop computers using DHCP (Dynamic Host Configuration Protocol)
- logical separation between subnets can be explained in terms of the IP address (in binary)
IPv4 Address Octets
- each octet in IP address has a value between 0 and 255
| 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 |
| — | — | — | — | — | — | — | — |
- let’s convert 192.168.10.15
| 128 |
64 |
32 |
16 |
8 |
4 |
2 |
1 |
| 1 (64) |
1 (0) |
0 (0) |
0 (0) |
0 (0) |
0 (0) |
0 (0) |
0 (0) |
| 128 |
64 |
32 |
16 |
8 |
4 |
2 |
1 |
| 128 |
64 |
32 |
16 |
8 |
4 |
2 |
1 |
| 1 (40) |
0 (40) |
1 (8) |
0 (8) |
1 (0) |
0 (0) |
0 (0) |
0 (0) |
| 128 |
64 |
32 |
16 |
8 |
4 |
2 |
1 |
| 0 (10) |
0 (10) |
0 (10) |
0 (10) |
1 (2) |
0 (2) |
1 (0) |
0 (0) |
| 128 |
64 |
32 |
16 |
8 |
4 |
2 |
1 |
| 0 (15) |
0 (15) |
0 (15) |
0 (15) |
1 (7) |
1 (3) |
1 (1) |
1 (0) |
11000000.10101000.00001010.00001111
Subnet masks
- to set boundary between logical networks (subnets), the IP address is combined with a subnet mask