CCNA Learning must be remembered

CCNA Learning must be remembered

-- hundred dishes

In the course of learning Xie Xiren's "computer network", we found that there are some very important knowledge points that are not broken in the books, which may be constantly updated in the new version, but in any case, we can often look at these knowledge points to strengthen our memory. In the course of continuous learning, bloggers will also add other content that they think is useful to beginners from time to time.

1. In the part of learning subnetting, it may be easy to ignore enabling 0 subnets: (enable command ip subnet-zero)

If you configure the routing interface with the address 192.168.10.6 255.255.255.248, the following error message appears:

"Bad mask / 29 for address 192.168.10.6"

This indicates that the command ip subnet-zero is not enabled. The address used here belongs to subnet 0 (192.168.10.0tab 29).

two。 Some special addresses to remember:

127.0.0.1 loopback test address, which can test whether the local network card is normal.

Private address: class A 10.0.0.0-10.255.255.255

Class B 172.16.0.0-172.31.255.255

Class C 192.168.0.0-192.168.255.255

Private addresses are not routable on the Internet. That is, the host cannot surf the Internet after configuring the private address of this range.

The multicast address is Class D (244.0.0.0-239.255.255.255), and Class E is used for research.

The all-0 network address is reserved for specifying the default route (0.0.0.0 0.0.0.0)

3. Default subnet mask

Category A: 255.0.0.0

Category B: 255.255.0.0

Class C: 255.255.255.0

For class An addresses, the first byte must start with 255, and there are no specific requirements after that

For class B addresses, one or two bytes must be 255.255, after which there are no specific requirements

For a Class C address, it must start with 255.255.255, and then there are no specific requirements, as long as the mask format is met.