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SNR S2989G-24TX-POE Руководство по настройке онлайн [150/553] 747270
2-86
S2989G-24TX Operation Manual Chapter 2 Layer 2 services
Configuration
Figure 2-29 generic VLAN network
VLAN
IP Subnet
Gateway
Address
Usable
Hosts
Customer
Hosts
Needed
Hosts
21
1.1.1.0/28
1.1.1.1
14
13
10
22
1.1.1.16/29
1.1.1.17
6
5
5
23
1.1.1.24/30
1.1.1.25
2
1
1
Tab 1-1 host address division of generic VLAN
In above table, the needed hosts may be 10 in VLAN 21 and assign a subnet with mask of
28 bits—1.1.1.0/28. However, subnet 1.1.1.0 of network segment, subnet broadcast
address 1.1.1.15 and the default gateway address 1.1.1.1 can not become the host
address, address range within 1.1.1.2 to 1.1.1.14 can become the host address. So the
usable host addresses total is 13 (2
32-28
-3=13), however, only 10 addresses can satisfy
the requirement for VLAN21.
The rest may be deduced by analogy, the needed host addresses is 5 for VLAN 22.
To satisfy request, it needs to assign a subnet with mask of 29 bits (1.1.1.16/29) for VLAN
22. The needed host address is only 1 for VLAN 23, but it occupies subnet 1.1.1.24/30.
The needed addresses is 16 (10+5+1) for three VLANs, but the excellent method also
occupies 28 addresses (2
32-28
+2
32-29
+2
32-30
=28) according to address division of generic
VLAN, so waste many addresses. Besides, if the needed hosts only reach to 3, but not to
10 hosts, and a subnet with mask of 28 bits is assigned to VLAN 21 before, here, the
redundant addresses are wasted because they can not be used by other VLAN.
The above division is difficult to network update. If client of VLAN23 needs to add 2
hosts and client does not want to change the assigned IP address, but the addresses after
1.1.1.24 are assigned to others, so we should assign a subnet with mask of 29 bits and a
new VLAN to this client. Here, there are 3 hosts for client of VLAN23 only, but this client is

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