IP

IP uses packets or L3 PDU.

Network Address Classes

• A class 1-126. First bit is zero(0)


• B class 128-191 second bit is zero (10)


• C class 192-223 third bit is zero (110)


• D class 224-239 224.0.0.0 and goes through 239.255.255.255 – multicast addresses.


• E class 240-255

Some facts

• Network address of all 0s is reserved and interpreted to mean “this network or segment.”


• Network address of all 1s is reserved and interpreted to mean “all networks.”


• Network 127.0.0.1 is reserved for loopback tests. Designates the local node and allows that node to send a test packet to itself without generating network traffic.


• Node address of all 0s Interpreted to mean “network address” or any host on specified network.


• Node address of all 1s Interpreted to mean “all nodes” on the specified network; for example, 128.2.255.255 means “all nodes” on network 128.2 (Class B address)


• Entire IP address set to all 0s Used by Cisco routers to designate the default route. Could also mean “any network.”


• Entire IP address set to all 1s (same as 255.255.255.255)Broadcast to all nodes on the current network; sometimes called an “all 1s broadcast” or limited broadcast.


• ip subnet zero - you can use 0 subnet in configuration.


• Configuring default gateway in Cisco
  

Reserved IP Address Space

• Class A 10.0.0.0 through 10.255.255.255


• Class B 172.16.0.0 through 172.31.255.255


• Class C 192.168.0.0 through 192.168.255.255


• 127.0.0.1


• 169.254.0.0/16 – auto configuration ip addresses.

Addresses that can't be used as unicasts:

• 127 network


• 224-239


• 240-255


• Subnet number


• Subnet broadcast

Troubleshooting

• Shows detailed information about interfaces with ip configured.

show ip interfaces

• Shows short information about interfaces(no subnet mask) with ip configured.

show ip interfaces brief