Configure DHCP IPv4 Reservation on FTD Using FlexConfig
Author: Cisco Systems, Inc.
Date: 2026-09-18T05:00:00+00:00
Description: An administrator wants to configure a Firewall Threat Defense (FTD) device as a DHCP server for a workstation and set up a DHCP address reservation.

Contents

Issue

- An administrator wants to configure a Firewall Threat Defense (FTD) device as a DHCP server for a workstation and set up a DHCP address reservation for an endpoint device.

- The configuration involves configuring DHCP server for the FTD natively in the Firewall Management Center (FMC) and using FlexConfig to add the DHCP IP reservation.

Environment

- Firewall Threat Defense (FTD) version 10.x. Other software versions are also affected.

- Firewall Management Center (FMC) 10.x. Other software versions are also affected.

Topology

The specific DHCP environment includes:

- DHCP server interface is NET200.

- DHCP server pool is 192.0.2.10 - 50.

- Endpoint device with MAC address 0000.5E00.5301. The goal is to reserve IP address 192.0.2.45 for this endpoint.

Resolution

DHCP Server Configuration

The pool 192.0.2.10 - 50 is configured on FTD interface NET200:

FlexConfig Configuration

For the DHCP IP address reservation use FlexConfig:

- Deployment Type: Set to "Once".

- Configuration Type: Set to "Append" (this is the default). "Prepend" can be also used.

Configuration Validation

The deployed configuration:

device# show run dhcpd

dhcpd address 192.0.2.10-192.0.2.50 NET200

dhcpd enable NET200

dhcpd reserve-address 192.0.2.45 0000.5E00.5301 NET200

Background Operation

To capture the DHCP packets use these commands:

device#  capture CAPI interface NET200 match udp any any eq bootpc

device#  capture CAPI interface NET200 match udp any any eq bootps

- The DHCP client listens on UDP port 68.

- The DHCP server listens on UDP port 67.

DHCP debugs:

device# debug dhcpd event 255

debug dhcpd event enabled at level 255

device# debug dhcpd packet 255

debug dhcpd packet enabled at level 255

Note: Use debugs with caution!

Debug output during the IP address assignment:

DHCPD/RA:  Server msg received, fip=ANY, fport=0 on NET200 interface

DHCPD: DHCPDISCOVER received from client 0100.5056.885f.d1 on interface NET200.

DHCPD:IP 248.57.222.26 ARP entry removed from the cache

DHCPD: send ping pkt to 192.0.2.45

DHCPD: ping got no response for ip: 192.0.2.45

DHCPD: MAC 0000.5E00.5301 is reserved for IP 192.0.2.45, allocating it

DHCPD: Add binding 192.0.2.45 to radix tree

DHCPD/RA: Binding successfully added to hash table

dhcpd_create_automatic_binding() adding NP rule for client 192.0.2.45

DHCPD: assigned IP address 192.0.2.45 to client 0100.5056.885f.d1.

DHCPD: Sending DHCPOFFER to client 0100.5056.885f.d1 (192.0.2.45).

DHCPD: Total # of raw options copied to outgoing DHCP message is 0.

DHCPD/RA: creating ARP entry (192.0.2.45, 0000.5E00.5301).

DHCPD: unicasting BOOTREPLY to client 0000.5E00.5301(192.0.2.45).

DHCPD/RA:  Server msg received, fip=ANY, fport=0 on NET200 interface

DHCPD: DHCPDISCOVER received from client 0100.5056.885f.d1 on interface NET200.

DHCPD: Sending DHCPOFFER to client 0100.5056.885f.d1 (192.0.2.45).

DHCPD: Total # of raw options copied to outgoing DHCP message is 0.

DHCPD/RA: creating ARP entry (192.0.2.45, 0000.5E00.5301).

DHCPD: unicasting BOOTREPLY to client 0000.5E00.5301(192.0.2.45).

DHCPD/RA:  Server msg received, fip=ANY, fport=0 on NET200 interface

DHCPD: DHCPDISCOVER received from client 0100.5056.885f.d1 on interface NET200.

DHCPD: Sending DHCPOFFER to client 0100.5056.885f.d1 (192.0.2.45).

DHCPD: Total # of raw options copied to outgoing DHCP message is 0.

DHCPD/RA: creating ARP entry (192.0.2.45, 0000.5E00.5301).

DHCPD: unicasting BOOTREPLY to client 0000.5E00.5301(192.0.2.45).

DHCPD/RA:  Server msg received, fip=ANY, fport=0 on NET200 interface

DHCPD: DHCPREQUEST received from client 0100.5056.885f.d1.

DHCPD: Extracting client address from the message

DHCPD: State = DHCPS_REBOOTING

DHCPD: State = DHCPS_REQUESTING

DHCPD: Client 0100.5056.885f.d1 specified it's address 192.0.2.45

DHCPD: Client is on the correct network

DHCPD: Client accepted our offer

DHCPD: Client and server agree on address 192.0.2.45

DHCPD: Renewing client 0100.5056.885f.d1 lease

DHCPD: Client lease can be renewed

DHCPD: Sending DHCPACK to client 0100.5056.885f.d1 (192.0.2.45).

DHCPD: Including FQDN option name 'DESKTOP-VQ7968K' rcode1=0, rcode2=0 flags=0x0

DHCPD: Total # of raw options copied to outgoing DHCP message is 0.

DHCPD/RA: creating ARP entry (192.0.2.45, 0000.5E00.5301).

DHCPD: unicasting BOOTREPLY to client 0000.5E00.5301(192.0.2.45).

Verification of the DHCP binding:

device# show dhcpd binding

IP address       Client Identifier        Lease expiration        Type

192.0.2.45    0100.005e.0053.01            3589 seconds    Automatic

Cause

- FMC does not natively support the configuration of DHCP IP address reservation. Thus, FlexConfig has to be used to configure the IP address reservation.

- Related enhancement defect: Cisco bug ID CSCwn24229.

Related Content

- https://www.cisco.com/c/en/us/td/docs/security/asa/asa-cli-reference/A-H/asa-command-ref-A-H/m_dh-dm.html#wp1603069952

- https://bst.cloudapps.cisco.com/bugsearch/bug/CSCwn24229

- Cisco Technical Support & Downloads