Configuring Dhcp Server Port-Based Address Allocation; Information About Configuring Dhcp Server Port-Based Address Allocation; Default Port-Based Address Allocation Configuration; Port-Based Address Allocation Configuration Guidelines - Cisco Catalyst 2960-XR Security Configuration Manual

Configuring DHCP
If DHCP snooping is enabled and an interface changes to the down state, the switch does not delete the
Note
statically configured bindings.

Configuring DHCP Server Port-Based Address Allocation

Information About Configuring DHCP Server Port-Based Address Allocation

DHCP server port-based address allocation is a feature that enables DHCP to maintain the same IP address
on an Ethernet switch port regardless of the attached device client identifier or client hardware address.
When Ethernet switches are deployed in the network, they offer connectivity to the directly connected devices.
In some environments, such as on a factory floor, if a device fails, the replacement device must be working
immediately in the existing network. With the current DHCP implementation, there is no guarantee that DHCP
would offer the same IP address to the replacement device. Control, monitoring, and other software expect a
stable IP address associated with each device. If a device is replaced, the address assignment should remain
stable even though the DHCP client has changed.
When configured, the DHCP server port-based address allocation feature ensures that the same IP address is
always offered to the same connected port even as the client identifier or client hardware address changes in
the DHCP messages received on that port. The DHCP protocol recognizes DHCP clients by the client identifier
option in the DHCP packet. Clients that do not include the client identifier option are identified by the client
hardware address. When you configure this feature, the port name of the interface overrides the client identifier
or hardware address and the actual point of connection, the switch port, becomes the client identifier.
In all cases, by connecting the Ethernet cable to the same port, the same IP address is allocated through DHCP
to the attached device.
The DHCP server port-based address allocation feature is only supported on a Cisco IOS DHCP server and
not a third-party server.

Default Port-Based Address Allocation Configuration

By default, DHCP server port-based address allocation is disabled.

Port-Based Address Allocation Configuration Guidelines

• By default, DHCP server port-based address allocation is disabled.
• To restrict assignments from the DHCP pool to preconfigured reservations (unreserved addresses are
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not offered to the client and other clients are not served by the pool), you can enter the reserved-only
DHCP pool configuration command.
Catalyst 2960-XR Switch Security Configuration Guide, Cisco IOS Release 15.0(2)EX1
Configuring DHCP Server Port-Based Address Allocation
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