6-2
In addition to assigning IP addresses to DHCP clients on public networks, a multi-VPN-instance
customer edge (MCE) device serving as the DHCP server can also assign IP addresses to DHCP
clients on private networks. Note that the IP address ranges of public and private networks or those of
private networks on the DHCP server cannot overlap each other. For details about MCE,
see MCE
Configuration in the Layer 3 - IP Routing Configuration Guide
.
DHCP Address Pool
Address pool types
DHCP address pools can be classified into two types:
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Common address pool: Supports both static binding and dynamic allocation.
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Extended address pool: Supports dynamic allocation only.
Common address pool structure
In response to a client’s request, the DHCP server selects an idle IP address from an address pool
and sends it together with other parameters such as the lease time and a DNS server address to the
client.
The common address pool database is organized as a tree. The root of the tree is the address pool for
natural networks, branches are address pools for subnets, and leaves are addresses statically bound
to clients. For the same level address pools, a previously configured pool has a higher selection
priority than a new one.
At the very beginning, subnetworks inherit network parameters and clients inherit subnetwork
parameters. Therefore, common parameters, for example a DNS server address, should be
configured at the highest (network or subnetwork) level of the tree.
After establishment of the inheritance relationship, the new configuration at the higher level (father) of
the tree will be:
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Inherited if the lower level (child) has no such configuration, or
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Overridden if the lower level (child) has such configuration.
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The extended address pool database is not organized as a tree.
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The IP address lease does not enjoy the inheritance attribute.
Principles for selecting an address pool
The DHCP server observes the following principles to select an address pool when assigning an IP
address to a client:
1) If there is an address pool where an IP address is statically bound to the MAC address or ID of
the client, the DHCP server will select this address pool and assign the statically bound IP
