DHCP-Server IPv4

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Setting up the DHCP server for an IPv4 network

Last adaptation to the version: 12.7.0

New:

• Adjustment in IP address allocation when Rejecting Unknown Clients is used.
• Detailed logging in the DHCP settings

Last updated: 

12.2024
• Prepare corrections in the IP address under Prepare IP address ranges

notempty

This article refers to a Resellerpreview

12.6 12.5 12.4 11.8.4 11.7

Access: Admin Interface of the UTMUTM-IP:Port or UTM-URL:Port
Port as configured at Network / Appliance Settings / Webserver
Default-Port: 11115
i.e.: https://utm.ttt-point.de:11115
Default: https://192.168.175.1:11115 Network Network Configuration

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Prepare IP address ranges

Network configuration UTMuser@firewall.name.fqdnNetwork Network interfaces

For the firewall to function as a DHCP server in a network, a fixed IP from the network range must be configured on the corresponding interface. In this example, IP addresses are assigned in network 192.168.222.0/24. To achieve this, an IP from this network is added to the interface. LAN3 → → IP addresses → In the selection box, enter or select the IP address from the desired network with the desired subnet mask, if applicable. Here 192.168.222.1/24

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Set up DHCP server

Network configuration UTMuser@firewall.name.fqdnNetwork DHCP-Pools

Under Network Network Configuration  Area DHCP Pools multiple DHCP pools can be added.
After clicking Add Pool, the setup wizard opens and the DHCP parameters can be specified.

Add pool UTMuser@firewall.name.fqdnNetworkNetwork configuration

Step 1: Name and IP range

Step 1 requires the Name for the pool and the valid IP range for the DHCP.
In the example, the following IP addresses are assigned
Pool start address: 192.168.222.150/--- 
Pool end address: 192.168.222.170/--- 

Add pool UTMuser@firewall.name.fqdnNetworkNetwork configuration

Step 2: Nameserver

In step 2, the DNS server for the DHCP clients can be specified.
Either the IP of a public DNS server or the IP of the firewall itself can be entered here. In this example, the clients use the firewall itself as DNS.notempty

In order for the UTM to also answer the DNS queries from the internal network, a corresponding rule is required.

Add pool UTMuser@firewall.name.fqdnNetworkNetwork configuration

Step 3: Router + Options

In step 3 of the wizard, the default gateway of the DHCP clients is specified.
Caution: Normally, the IP of the firewall is always entered here.notempty

An incorrect entry in this field may prevent access to the Internet!

Edit pool

After the pool has been created correctly, the pool start and end address can be changed and other parameters of the DHCP pool can be set up to be passed to the DHCP client.

General

Edit pool UTMuser@firewall.name.fqdnNetworkNetwork configuration Edit pool general area

Changes to the pool range start and pool range end possible

Options - DHCP Optionen

Option	Option number	Value	Description	Edit pool UTMuser@firewall.name.fqdnNetworkNetwork configuration Edit pool general area
Router:	3	»192.168.222.1	Router configured as in step 3
Domain name:	15	securepoint.local	Name of the domain in which the DHCP leases are assigned
Domain name server:	5	»192.168.222.1	Name server as configured in step 2
Netbios name server:	44		NetBIOS over TCP/IP Name Server Option
SMTP-Server:	69		Simple Mail Transport Protocol (SMTP) Server Option
NTP Server:	41		Servers should be listed in order of preference.
Vendor Encapsulated Options:	43		Values must be given coded.
TFTP Server Name:	66	profile.gigaset.net	The IPv4 address, or the hostname of the TFTP server ‍ option tftp-server-name text;
Bootfile Name:	67		The name of the bootfile file ‍ option bootfile-name text;
Default URL:	114	https://teamwork.gigaset.com/gigawiki/display/GPPPO/DHCP+option+114	Default URL ‍ option default-url string;
VLAN ID:	132		The ID of the VLAN used ‍ option vlan-id code 132 = text; option vlan-id "128";
Next Server:			The IPv4 address of the Next server If the value is missing, TFTP may not work.
Default Lease Time:	51	600 Seconds	Default validity period of the IP address if the client has not requested an explicit duration.
Maximal Lease Time:		7200 Seconds	Maximum validity period of the IP address in seconds that the client may receive when explicitly requested.
Reject unknown clients:		No	If activated Yes, an IP address is only assigned if there is a entry at Static DHCP tab for the MAC address of the client. notempty Changed standard behaviourab v12.7: The static lease entry for the DHCP must be in the same pool to be considered known. ‍ The static lease entry for the DHCP must be in the same pool to be considered known.

DHCP Setup

The Setup button opens a dialogue for the DHCP settings.

Caption	Value	Description	DHCP Setup UTMuser@firewall.name.fqdnNetworkNetwork configuration DHCP Setup
Ignore other SDHCP-Servers:	Off	When activated, other DHCP servers notempty New: IPv4 and IPv6 are ignored
Enable detailed logging: notempty New	Off	When activated, all DHCP requests are recorded in the syslog.

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Static DHCP

If hosts are to be assigned predefined IP addresses ( fixed IPs bound to the MAC address, but assigned by the UTM), these IPs can be reserved with static leases:
Configuration under Network Network Configuration  Area Static DHCP Button Add Lease

Host:	MaxMustermann-Laptop	Meaningful host name	Add lease UTMuser@firewall.name.fqdnNetworkNetwork configuration Dialogue Add lease
Ethernet:	12:34:56:78:90:AB	MAC address of the host
IP:	192.168.222.111/---	IP address to be reserved exclusively for this host
Save and close		Saves and accepts the lease and closes the creation dialogue.
notempty Important: Leases must necessarily be in an existing DHCP pool!			Network configuration UTMuser@firewall.name.fqdnNetwork Static DHCP
notempty Joint use of static and dynamic IP addresses within a pool is possible.

Static leases outside a pool

Existing static leases that are not within a DHCP pool must be changed! If such leases are detected after an update, a message is displayed prompting to adjust the DHCP settings. It ist now possible that either the leases are adapted and relocated in existing pools or additional DHCP pools are created that contain static leases or existing DHCP pools are extended so that they include static leases			Warning at login

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Widget

In the administrator interface of the UTM, there is a DHCP widget that provides an overview of the existing DHCP connections.
Further information can be found in the Wiki article UTM Widgets.