Hello everyone,
Today I will introduce you to a concept similar to subnets-Supernetting.
What is Supernetting
IP addresses are divided into separate network addresses and host addresses based on subnet masks. Supernetting, also known as Classless Inter-Domain Routing (CIDR), is a method of aggregating multiple Internet addresses of the same type.
Subnetting has reduced the pressure of tight IP address space to a certain extent. However, due to incomplete consideration in the initial stage of IP address allocation, a large number of Class A and Class B addresses are allocated at the beginning, and resources are quite tight, and some medium-sized networks require If there is more than one C address, only a few consecutive C-type address blocks can be allocated. In order to reduce the number of Internet routing tables, the concept of supernets is proposed. The definitions of supernets and subnets are just the opposite, which is to borrow a network bit as the host bit. So as to achieve the purpose of reducing the Internet routing table. For example, the four class C address segments 192.168.0/24-192.168.3/24 can be supernetted into a supernet like 192.168.0/22.
Supernet combine network segment
1. Combine network segments
Example: An enterprise has a network segment, the network segment has 200 hosts, and the network segment 192.168.0.0 255.255.255.0 is used.
Later, the number of computers increased to 400, and the network segment 192.168.1.0 255.255.255.0 was used for the 200 hosts added later, as shown below:
After the router is configured with an IP address interface of 192.168.0.1, and then the 192.168.1.1 address is added, the hosts in the two network segments 192.168.0.0 and 192.168.1.0 can communicate through the router forwarding.
So is there a better way to make these two Class C network segment computers think that they are in the same network segment?
This requires the merging of two Class C networks, 192.168.0.0/24 and 192.168.1.0/24.
Network segment merging: The subnet mask is moved forward by 1 bit so that the network part remains the same as the previous part.
Note: The subnet mask is shifted by 1 bit to the left, and two consecutive network segments can be merged, but not any consecutive network segments can be merged.
After merging the network segments, as shown in the figure below, all hosts will no longer communicate with each other through the router.
(1). After the merger, the network segment is 192.168.0.0/23, and the IP allocation is as follows:
(2). After the merger, the IP address 192.168.0.255/23 can also be used by the computer, because the host part adds a bit of 0 (not all 1s) to the left, as shown in the following figure:
2. Not any continuous network segments can be merged
For example, the following two consecutive network segments cannot be merged (move one bit forward, the network part cannot remain the same).
If you have to merge, you have to move 2 bits forward. At this time, the network part remains the same. In this way, 4 network segments are merged, as shown in the following figure:
3. Which continuous network segments can be merged
(1) Determine whether the two network segments can be merged
After the subnet mask is moved to the left by the corresponding number of bits, the network part can remain the same to be merged.
Conclusion: Determine whether two consecutive network segments can be merged. As long as the first network number is divisible by 2, it can be merged by shifting the subnet mask to the left by 1 bit.
(2) Determine whether the 4 network segments can be merged
Conclusion: Determine whether the consecutive 4 network segments can be merged. As long as the first network number is divisible by 4, it can be merged by shifting the subnet mask by 2 bits to the left.
By analogy, in order to judge whether 8 consecutive network segments can be merged, as long as the first network number is divisible by 8, these 8 consecutive network segments can be merged by shifting the subnet mask by 3 bits to the left.
4. The law of network segment merging
Shifting the subnet mask to the left by 1 bit can merge two network segments, shifting it by 2 digits left, merging four network segments, shifting it by 3 digits left, and merging 8 network segments.
5. Determine whether a network segment is a supernet or a subnet
(1). Merge multiple network segments by shifting the subnet mask to the left, and divide a network segment into multiple subnets by shifting the subnet mask to the right, so that the IP address breaks the traditional boundaries of Class A, Class B, and Class C.
(2). To determine whether a network segment is a subnet or a supernet, it depends on whether the network segment is a type A network, a type B network, or a type C network. The default type A subnet mask is /8, and the type B subnet masks. The code is /16, and the C-type subnet mask is /24.
(3). If the subnet mask of the network segment is longer than the default subnet mask, it is a subnet; if the subnet mask of the network segment is shorter than the default subnet mask, it is a supernet.
That is all I want to share with you!
