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Procedure
To configure a DHCP address pool on the DHCP relay agent:
Step
1.
Enter system view.
2.
Create a DHCP address
pool and enter its view.
3.
Specify gateway addresses
for the clients matching the
DHCP address pool.
4.
Specify DHCP servers for
the DHCP address pool.
Specifying the DHCP server selecting algorithm
About DHCP server selecting algorithm
The DHCP relay agent supports the polling and master-backup DHCP server selecting algorithms.
By default, the DHCP relay agent uses the polling algorithm. It forwards DHCP requests to all DHCP
servers. The DHCP clients select the DHCP server from which the first received DHCP reply comes.
If the DHCP relay agent uses the master-backup algorithm, it forwards DHCP requests to the
master DHCP server first. If the master DHCP server is not available, the relay agent forwards the
subsequent DHCP requests to a backup DHCP server. If the backup DHCP server is not available,
the relay agent selects the next backup DHCP server, and so on. If no backup DHCP server is
available, it repeats the process starting from the master DHCP server.
The master DHCP server is determined in one of the following ways:
•
In a common network where multiple DHCP server addresses are specified on the DHCP relay
interface, the first specified DHCP server is the master. The other DHCP servers are backup.
•
In a network where DHCP address pools are configured on the DHCP relay agent, the first
specified DHCP server in a DHCP address pool is the master. The other DHCP servers in the
DHCP address pool are backup.
DHCP server selection supports the following functions:
•
DHCP server response timeout time—The DHCP relay agent determines that a DHCP
server is not available if it does not receive any response from the server within the DHCP
server response timeout time. The DHCP server response timeout time is configurable and the
default is 30 seconds.
•
DHCP server switchback—If the DHCP relay agent selects a backup DHCP server, it does not
switch back to the master DHCP server by default. You can configure the DHCP relay agent to
switch back to the master DHCP server after a delay. If the master DHCP server is available,
the DHCP relay agent forwards DHCP requests to the master DHCP server. If the master
DHCP server is not available, the DHCP relay agent still uses the backup DHCP server.
Command
system-view
dhcp server ip-pool pool-name
gateway-list ip-address&<1-64>
[ export-route ]
remote-server
ip-address&<1-8>
136
Remarks
N/A
By default, no DHCP address pools
exist.
By default, no gateway address is
specified.
By default, no DHCP server is
specified for the DHCP address
pool.
You can specify a maximum of eight
DHCP servers for one DHCP
address pool for high availability.
The relay agent forwards DHCP
DISCOVER and REQUEST packets
to all DHCP servers in the DHCP
address pool.
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Troubleshooting
