In the default ip-address-first matching, the server selects the address-assignment pool
to use by matching the IP address in the client DHCP request with the network address
of the address-assignment pool. If the client request contains the gateway IP address
(giaddr), the local server matches the giaddr to the address-assignment pool’s address.
If there is no giaddr in the request, then the DHCP local server matches the IP address of
the receiving interface to the address of the address-assignment pool.
For IPv4 address-assignment pools, you can optionally configure the extended DHCP
local server to match the DHCP relay agent information option (option 82) in the client
DHCP packets to a named range in the address-assignment pool used for the client.
Named ranges are subsets within the overall address-assignment pool address range,
which you can configure when you create the address-assignment pool.
NOTE: To use the DHCP local server option 82 matching feature with an IPv4
address-assignment pool, you must ensure that the option-82 statement is
included in the dhcp-attributes statement for the address-assignment pool.
You can optionally include the option-82-strict method in the pool-match-order statement
for matching the address-assignment pool. If you include the option-82-strict method,
the extended DHCP local server applies the ip-address-first matching method first and
then uses the option-82 method to select the address-assignment pool. The
ip-address-first method must be specified before the option-82-strict method in the
pool-match-order list.
NOTE: If the option-82-strict method is configured in the pool-match-order
list, any DHCP discover packet with either unknown or no option-82
information will be denied with an IP address. A DHCP client is allocated with
an IP address only when the DHCP packet matches the option-82 information
configured as a part of the dhcp-attributes statement. If dhcp-attributes to
match for specific option-82 value is not configured as a part of the selected
pool configuration, the option-82-strict match order option will have no effect
and IP addresses are allocated by the DHCP local server by matching the
subnet of the incoming interface.
To configure the matching order the extended DHCP local server uses to determine the
address-assignment pool used for a client:
1. Access the pool-match-order configuration.
[edit system services dhcp-local-server]
user@host# edit pool-match-order
323Copyright © 2017, Juniper Networks, Inc.
Chapter 10: Configuring DHCP Client and DHCP Server
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