Huawei AR530 series Configuration Manual page 96

Huawei AR530&AR550 Series Industrial Switch Routers
Configuration Guide - Ethernet Switching
Table 3-3 Example of Assigning Host Addresses on a common VLAN
VLAN
2
3
4
As show in
the mask length as 28 bits is assigned for VLAN 2. 10.1.1.0 is the address of the sub network,
and 10.1.1.15 is the directed broadcast address. These two addresses cannot serve as the host
address. In addition, as the default address of the network gateway of the sub network, 10.1.1.1
cannot be used as the host address. The other 13 addresses ranging from 10.1.1.2 to 10.1.1.14
can be used by the hosts. In this way, although VLAN 2 needs only ten addresses, 13 addresses
need to be assigned for it according to the division of the sub network.
VLAN 3 requires five host addresses. The sub network 10.1.1.16/29 with the mask length as 29
bits needs to be assigned for VLAN 3. VLAN 4 requires only one address. The sub network
10.1.1.24/30 with the mask length as 30 bits needs to be assigned for VLAN 4.
In above, 16 (10+5+1) addresses are needed for all the preceding VLANs. However, 28 (16+8
+4) addresses are needed according to the common VLAN addressing mode even if the optimal
scheme is used. Nearly half of the addresses is wasted. In addition, if VLAN 2 is accessed to
three hosts instead of ten hosts later, the extra addresses will not be used by other VLANs and
will be wasted.
This division is inconvenient for the later network upgrade and expansion. Assume that two
more hosts need to be added to VLAN 4 and VLAN 4 does not want to change the assigned IP
addresses, and the addresses after 10.1.1.24 has been assigned to others, a new sub network with
the mask length as 29 bits and a new VLAN need to be assigned for the new customers of VLAN
4. Therefore, the customers of VLAN 4 have only three hosts, but the customers are assigned to
two sub networks and are not in the same VLAN. As a result, this is inconvenient for network
management.
In above, many IP addresses are used as the addresses of sub networks, directional broadcast
addresses of sub networks, and default addresses of network gateways of sub networks. These
IP addresses cannot be used as the host addresses in the VLAN. The limit on address assignation
reduces the addressing flexibility, so that many idle addresses are wasted. To solve this problem,
VLAN aggregation is used.
Principle
The VLAN aggregation technology, also known as the super-VLAN, provides a mechanism that
partitions the broadcast domain using multiple VLANs in a physical network so that different
VLANs can belong to the same subnet. In VLAN aggregation, two concepts are involved,
namely, super-VLAN and sub-VLAN.
Issue 01 (2014-11-30)
Sub- Gateway
network address
10.1.1.0/28 10.1.1.1
10.1.1.16/29 10.1.1.17
10.1.1.24/30 10.1.1.25
Table 3-3, VLAN 2 requires 10 host addresses. The sub network 10.1.1.0/28 with
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Number of Number of
available available
addresses hosts
14 13
6 5
2 1
3 VLAN Configuration
Practical
requirements
10
5
1
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