Five, IP address planning method
(1) Basic steps for IP address planning
Network address planning needs to be done in the following 6 steps:
a) Determine the user's demand for the number of networks and hosts;
b) Calculate the basic network address structure that satisfies the user's needs;
c) Calculating the address mask;
d) compute the network address;
e) Calculating the network broadcast address;
f) Compute the network host address.
(2) Basic methods of address planning
A) Step one: Determine the network and host number of requirements
According to the physical topology design of the network overall design is the parameter, determine the following two main data:
1) The maximum number of subnets that may be used in the network nnet;
2) The maximum number of network segments that are already present and possibly expanded is nhost.
b) Step two: Calculate the basic network address structure parameters that meet the user's needs
1) Select the length value of the SubnetID field X, which requires the X-Times of Nnet≤2
。 For example, if the number of subnets Nnet is 10, then select the length value of the SubnetID field to x=4,2 4 times
=16, which is larger than the maximum number of subnets that may be used 10, meets the requirements.
2) Select the length value y of the HostID field, and ask for the Y-order of the Nhost≤2
。 For example, if the number of subnet hosts is nhost to 12, select the length value of the HostID field to y=4,2 4 times
=16, which is larger than the maximum number of possible hosts 12, meets the requirements.
Note: A value of 0 for the HostID field indicates that the Netid,hostid field of the network has a value of 1 for the broadcast address of the network, so the maximum available host number is 14 when y=4. Meet the user requirements for this example.
3) Depending on the value of the x+y, you can determine which IP address to request.
Because in subnetting, the X+y value represents the sum of SubnetID and hostid lengths, for example X=4, y=4 in this case, the total length is 8, then a Class C address segment can meet the requirements. If you exceed 8bit, you will need to apply for 2 class C addresses or a class B address.
c) step three; address mask calculation
Based on the definition of the subnet mask, the address mask for a Class C network without subnetting is 255.255.255.0.
The address mask after subnetting is a standard 32-bit IP address higher than HostID (Y-bit) in the high position of 1, that is, the standard IP address needs to be the 4th 8bit of the first 4bit position 1, if in decimal notation is 128+64+32+16=240. Then the address mask is 255.255.255.240. If this class C address is 192.168.1.0, then it can be simply represented as 192.168.1.0/28.
D) Step four: Calculate network address
Because the address design chooses HostID length y=4, there are up to 14 hosts in each subnet. That is, the host address increment value for neighboring subnets is 16. Then the first network number in this example is 192.168.1.0, then the next network number is increased by 16 on this basis.
It is important to note that the first and last addresses are not used in the RFC document that describes the subnetting, that is, the 192.160.1.0 and 192.160.1.240 address numbers are not used in this case, but can be used if the TCP/IP protocol is set to allow.
E) Step five: Calculate the network broadcast address
According to the law, a subnet's directed broadcast address is a 1 smaller address number than the next subnet address number.
f) Step six: Compute the host address of the network
According to the law of address usage, the network address that excludes network address and broadcast address is the IP address that the host can use.
Six, subnet address planning method
(1) The basic methods and steps of subnet address planning
1 The following three steps are required to create a subnet:
A) determine the number of netid required.
1) Each subnet requires a netid.
2) Each WAN connection requires a netid.
b) Determine the number of HostID required
1) Each host needs a hostid.
2) Each connection to the router requires a hostid.
c) based on the above requirements, you need to create the following content
1) Set a subnet mask for the entire network;
2) set a different subnetid for each physical network segment;
3) Determine the host's legal address space for each subnet.
2 The subnet address plan needs to answer the following 5 basic questions:
A) How many subnets can be generated by this selected subnet mask?
b) How many legitimate subnetid can be within each subnet?
c) What are these legitimate host addresses?
D) What is the broadcast address for each subnet?
e) What is the legal netid within each subnet?
(2) Subnet Address planning example
1) User Requirements
A) a campus network to obtain a class B IP address 156.26.0.0), to be sub-network division.
b) The campus network will consist of nearly 210 networks.
c) In order to facilitate management, it is required to divide the subnets according to the current situation.
2). Determine the length of the subnet number SubnetID
A) consider that the number of subnets in the campus network is within 254, so a feasible subnetting scheme is to take the subnet number of the length of 8 bits. Such a subnet mask is 255.255.255.0.
b) because the host number HostID cannot use full 0 or all 1, so the campus network can only have 254 subnets, each subnet can only have 254 hosts.
c) In determining the length of the subnet, you should weigh the number of subnets and the number of hosts and routers in each subnet, not simply the number of subnets to pursue, must meet the basic requirements, and consider leaving a certain margin.
3) Determine the subnet address
In the above subnetting scheme, the IP address available on the campus network is:
Sub-network 1:256.26.1.1~156.26.1.254
Sub-network 2:256.26.2.1~256.26.2.254
Sub-network 3:256.26.3.1~256.26.3.254
......
Sub-network 254:256.26.254.1~256.26.254.254
Seven, variable length subnet mask (VLSM) Address planning method
(1) Variable length subnet mask (VLSM) Basic principles of address planning
The IP protocol allows the division of variable eldest sons (RFC1009) to be used. In some cases, it is necessary to design the subnet number length differently when subnetting.
VLSM (Variable length Subnet mask, variable length subnet mask), is the network number of the subnet that is divided on the standard mask, no
The class router chooses a network that can use VLSM, and VLSM is not available in a class-routed network.
(2) Case of variable length subnet mask (VLSM) address planning
1) User Requirements
A) a company has applied for an entire class C 202.60.31.0 IP address space.
b) The company has 100 employees working in the sales department and 50 employees working in the Finance Department.
c) Ask the network administrator to set up subnets for the sales department, finance department and design department respectively.
2) Select a variable-length subnet mask
A) In this case, a class C IP address can be divided into 3 parts through the variable length subnet mask (variablelengthsubnetmask,vlsm) technique, where the address space of Subnet 1 is twice times the Subnet 2 and the Subnet 3 address space.
The subnetting subnets are:
b) Compute Subnet 1 address space
You can first use a subnet mask of 255.255.255.128 to divide a class C IP address into two halves. In binary operations, the operation is:
IP address of Host: 11001010.00111100.00011111.00000000 (202.60.31.0)
Subnet Mask: 11111111.11111111.11111111.1000000 (255.255.255.128)
And operation Result: 11001010.00111100.00011111.00000000 (202.60.31.0)
The result of operation shows that 202.60.31.1~202.60.31.126 can be used as the IP address of Subnet 1. , and the remainder is further divided into two halves. Since the 202.60.31.127 4th byte is full 1, it is reserved as a broadcast address and cannot be used; Subnet 1 and Subnet 2, Subnet 3 's space junction point is at 202.60.31.128; Subnet 1 uses the subnet mask 255.255.255.128.
First time Borrow:
c) Compute Subnet 2 and Subnet 3 address space
The calculation process for the address space of Subnet 1 and Subnet 2 is:
IP address of Host: 11001010.00111100.00011111.00000000 (202.60.31.0)
Subnet Mask: 11111111.11111111.11111111.1000000 (255.255.255.128)
And operation Result: 11001010.00111100.00011111.00000000 (202.60.31.0)
You can divide the two smaller address spaces after the split to Subnet 2 and Subnet 3, the first available address is 202.60.31.129, and the last available address is 202.60.31.190. So the address available for Subnet 2 is 202.60.31.129~202.60.31.190.
Because the next address 202.60.31.191 191 is a full 1 address, it needs to be left as the broadcast address. The next address is 202.60.31.192, which is the first address of Subnet 3. Then the IP address of Subnet 3 should be from 202.60.31.192~202.60.31.254.
Second time borrow:
3) Determine the IP address space of the three subnets
The IP addresses of the three subnets that were divided by the variable eldest son network are:
A) Subnet 1 address space is: 202.60.31.1~202.60.31.126.
The subnet mask is: 255.255.255.128.
b) Subnet 2 address space is: 202.60.31.129~202.60.31.190.
The subnet mask is: 255.255.255.192.
c) Subnet 2 address space is: 202.60.31.193~202.60.31.254.
The subnet mask is: 255.255.255.192.
Subnet 1 allows a host number of 126, and Subnet 2 and Subnet 3 can use a host number of 61. This program can meet the requirements of the company.
The network structure for the entire scenario is:
Eight, CIDR address planning method
(1) Example of CIDR address planning method
A) user needs
If a campus network management Center obtains the 200.24.16.0/20 address block, it wants to divide it into 8 equal-length smaller address blocks.
b) determine the CIDR address
Borrowing the length of the host number
Borrowing the first three bits of 12 bits in a CIDR address (2 of 3
=8), can be further divided into 8 equal-length smaller address blocks for the purpose.
c) Division of Address blocks
Examples of partitioning:
Campus Address: 200.24.16.0/20
Computer Department Address: 200.24.16.0/23
Automation Department Address: 200.24.18.0/23
Electronic Department Address: 200.24.20.0/23
Department of physics Address: 200.24.22.0/23
Department of Biology Address: 200.24.24.0/23
Chinese Department Address: 200.24.26.0/23
Chemical Department Address: 200.24.28.0/23
Department of mathematics Address: 200.24.30.0/23
(2) Analysis of the partition structure
A) from the above example, it can be seen that for the computer system, it is assigned a 200.24.16.0/23 address block, its address block network prefix is 23 for the "11001000000110000001000"; the minimum starting address of the address block is
200.24.16.0 the address block can be assigned a number of 29 addresses
A. For the Automation department, it is assigned the 200.24.18.0/23 address block. Its address has a network prefix of 23 for "11001000000110000001001";
The minimum start address of the address block is 200.24.18.0/23. The number of addresses in the address block that can be assigned is 29
A. Similarly, 8 departments are given the same size of address space.
b) Analysis of network prefixes in computer systems and automation systems:
Network prefixes for computer systems: 11001000000110000001000
Network prefixes for automation systems: 11001000000110000001001
The first 20 bits of the network prefix assigned to the two lines are the same, and the first 20 of the network prefixes for the 8 address blocks are the same. This conclusion illustrates an important feature of CIDR addresses: the ability to address aggregation (addressaggregation) and Route aggregation (routeaggregation).
c) Campus network structure after the CIDR address block is divided
The structure of the campus network after dividing the CIDR address block, in which the main router of the Internet is trained to send an advertisement to the external network to indicate that it will receive the first 20 of the destination address as a group corresponding to the 200.24.16.0/20. Then the external network does not need to know that there are 8 system-level networks inside 200.24.16.0/20.
(3) Non-class inter-domain routing CIDR reception is typically used to merge multiple class C IP addresses into a single network, and use an entry in the routing table to represent these class C IP addresses.
The main applications of CIDR technology are:
A) to build a hyper-net
b) Route Aggregation
Copyright NOTICE: This article for Bo Master original article, without Bo Master permission not reproduced.
How to plan and design IP addresses (ii)
