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Catalyst 3750-X and 3560-X Switch Software Configuration Guide
OL-25303-03
Chapter 1 Configuring DHCP Features and IP Source Guard
Configuring DHCP Server Port-Based Address Allocation
After enabling DHCP port-based address allocation on the switch, use the ip dhcp pool global
configuration command to preassign IP addresses and to associate them to clients. To restrict
assignments from the DHCP pool to preconfigured reservations, you can enter the reserved-only DHCP
pool configuration command. Unreserved addresses that are part of the network or on pool ranges are
not offered to the client, and other clients are not served by the pool. By entering this command, users
can configure a group of switches with DHCP pools that share a common IP subnet and that ignore
requests from clients of other switches.
Beginning in privileged EXEC mode follow these steps to preassign an IP address and to associate it to
a client identified by the interface name.
To disable DHCP port-based address allocation, use the no ip dhcp use subscriber-id client-id global
configuration command. To disable the automatic generation of a subscriber identifier, use the no ip
dhcp subscriber-id interface-name global configuration command. To disable the subscriber identifier
on an interface, use the no ip dhcp server use subscriber-id client-id interface configuration command.
To remove an IP address reservation from a DHCP pool, use the no address ip-address client-id string
DHCP pool configuration command. To change the address pool to nonrestricted, enter the no
reserved-only DHCP pool configuration command.
In this example, a subscriber identifier is automatically generated, and the DHCP server ignores any
client identifier fields in the DHCP messages and uses the subscriber identifier instead. The subscriber
identifier is based on the short name of the interface and the client preassigned IP address 10.1.1.7.
switch# show running config
Building configuration...
Current configuration : 4899 bytes
Step 7
show running config Verify your entries.
Step 8
copy running-config startup-config (Optional) Save your entries in the configuration file.
Command Purpose
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
ip dhcp pool poolname Enter DHCP pool configuration mode, and define the
name for the DHCP pool. The pool name can be a
symbolic string (such as Engineering) or an integer
(such as 0).
Step 3
network network-number [mask | /prefix-length] Specify the subnet network number and mask of the
DHCP address pool.
Step 4
address ip-address client-id string [ascii] Reserve an IP address for a DHCP client identified by
the interface name.
string—can be an ASCII value or a hexadecimal
value.
Step 5
reserved-only (Optional) Use only reserved addresses in the DHCP
address pool. The default is to not restrict pool
addresses.
Step 6
end Return to privileged EXEC mode.
Step 7
show ip dhcp pool Verify DHCP pool configuration.
Step 8
copy running-config startup-config (Optional) Save your entries in the configuration file.
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