INI FILE OVERVIEW
The
INI file “dhcpsrv.ini” is the configuration and the “database” for
the DHCP Server. Its location is in the same directory as the dhcpsrv.exe
file. Here are typical examples of the INI file content:
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Example
1: The server has only one NIC and manages clients on the same subnet
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This is a very simple example and the INI file looks like this:
[General]
SUBNETMASK=255.255.255.0
ROUTER_1=192.168.10.1
DNS_1=192.168.10.1
[Settings]
IPPOOL_1=192.168.10.2-49
This
manages the IP addresses 192.168.10.2 until 192.168.10.49. But be aware
that all clients connected to the subnet 192.168.10.X get IP addresses
assigned. Please make sure that you don’t get in conflict with other
DHCP Servers.
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Example
2: The server has 2 or more NICs and manages
clients on one of the subnets
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The INI file looks like this:
[General]
SUBNETMASK=255.255.255.0
ROUTER_1=192.168.10.1
DNS_1=192.168.10.1
[Settings]
IPBIND_1=192.168.10.1
IPPOOL_1=192.168.10.2-49
This
manages the IP addresses 192.168.10.2 until 192.168.10.49. The DHCP
Server binds only to one NIC with the IP address 192.168.10.1. The
other NIC (Ethernet 2) is not touched by the DHCP Server. This is very
useful if Ethernet 2 is your company LAN and you don’t want to
interfere with it.
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Example
3: The server has 2 or more NICs and manages
clients on two subnets
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The INI file looks like this:
[General]
SUBNETMASK=255.255.255.0
ROUTER_1=192.168.10.1
DNS_1=192.168.10.1
[Settings]
AssociateBindsToPools=1
IPBIND_1=192.168.10.1
IPBIND_2=192.168.11.1
IPPOOL_1=192.168.10.2-49
IPPOOL_2=192.168.11.2-49
This
manages the IP addresses 192.168.10.2 until 192.168.10.49 for Ethernet
1 and 192.168.11.2 until 192.168.11.49 for Ethernet 2. Please note the
line AssociateBindsToPools=1. This option associates the IP Pools with
the corresponding IP Binds. Without that option the DHCP Server would
view all IPPOOL_x as one big IP pool independent of the subnet.
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The
different INI file sections
The INI file consists of sections for configuration purposes: [Settings], [DNS-Settings],
[Servers] and database purposes: [General], [General_x], and [client section name].
The examples above contained
the [Settings] section and the [General] section. The [Settings]
section holds all the configuration data for the DHCP server itself.
Most importantly the IP pools that the DHCP Server is supposed to
manage.
The idea behind the database sections is very simple. The DHCP Server tries first
to obtain the requested information from the client section then form the [General_x]
section and then from the [General] section. The client sections are created as clients
connect. For example:
For example:
[00-E0-00-1C-AB-67]
IPADDR=192.168.10.11
AutoConfig=12/29/2007 18:37:26
LeaseEnd=1198953446
This
section is added automatically by the DHCP Server when a client with
the MAC address 00-E0-00-1C-AB-67 requests an IP address. Here, the IP
address 192.168.10.11 has been assigned and the IP address will expire
at a certain time which is stored as number of seconds since midnight
(00:00:00), January 1, 1970.
If the client section does not include all requested information, then the DHCP
Server checks the [General_x] section and the [General] section.
The complete set of data that the
DHCP Server transmits to the client is composed of the entries
in the client section [00-E0-00-1C-AB-67], the [General_x] and the [General] section.
Please
note that with V1.7 it is possible to use the client-identifier (option 61) instead of the mac address
to specify client sections. See also the UseClientID setting defined in the INI
file reference.
In case of client-id based specifications, all the [00-E0-00-1C-AB-67] sections will actually be defined
based on the client supplied option 61. This can be a name (ascii string) or a mac address.
The [General_x] sections are optional but needed to define NIC specific information. Where
x is the same number as in IPBIND_x. It is possible to define NIC specific [General_x]
sections, in case that the subnets have different subnet masks or different lease times.
The following example is an extension of example 3 and defines a lease time of 1 hour for
clients connected to Ethernet 1 and a lease time of 1 day for clients connected to Ethernet 2.
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[General]
SUBNETMASK=255.255.255.0
ROUTER_1=192.168.10.1
DNS_1=192.168.10.1
[General_1]
LEASETIME=3600 ; default
lease time of 1 hour
[General_2]
LEASETIME=86400 ; default
lease time of 1 day
[Settings]
AssociateBindsToPools=1
IPBIND_1=192.168.10.1
IPBIND_2=192.168.11.1
IPPOOL_1=192.168.10.2-49
IPPOOL_2=192.168.11.2-49
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Lease
times are important when a client requests an IP address and all
addresses in the IP pool are already assigned to other clients. In
that case the client whose lease time has expired least recently is
deleted from the INI file and the available IP address is used for the
request. The lease time is calculated as the minimum of what the
client requests and the LEASETIME configured in the INI file. Clients
will request an extension of the lease in time before the lease
expires. If the LEASETIME is set to only a few seconds then the
network will be constantly full of traffic with lease extension
requests.
It
is also possible to add client sections to the INI file manually. The
following client section assigns the client with the MAC address
00-E0-00-1C-AB-68 the IP address 192.168.10.50.
[00-E0-00-1C-AB-68]
IPADDR=192.168.10.50
This
is a static assignment and is not changed or deleted by the DHCP
Server. It is important to not specify the AutoConfig=xxxxx entry in
the client section, otherwise the DHCP Server would consider this as
an automatically created client section. The INI file may contain
static entries only. This can be a useful way of limiting the clients
on the network to only known and allowed computers. The IPPOOL_x
should be removed from the INI file in case of fully static
assignments. Here is an example for fully static configurations:
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Example
4: Static configuration on one subnet
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The INI file looks like this:
[General]
SUBNETMASK=255.255.255.0
LEASETIME=32000000 ; approx. 1 year
ROUTER_1=192.168.10.1
DNS_1=192.168.10.1
[Settings]
IPBIND_1=192.168.10.1
IgnoreUnknownClients=1
[00-E0-00-1C-AB-68] ; Client 2
IPADDR=192.168.10.50
[00-E0-00-1C-AB-67] ; Client 1
IPADDR=192.168.10.11
Please
note the line IgnoreUnknownClients=1. This option prevents the DHCP Server
from sending answers to clients that are not configured in the INI file.
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DNS Server configuration
The [DNS-Settings] section consists of the settings for the integrated DNS server.
This is a new feature of V1.8 and lets the DHCP Server on the same data (ini file)
also handle DNS requests. This is done based on the IPADDR and Hostname entries of the
the configured clients. The supported DNS requests are A (IP->hostname) and PTR (hostname -> IP).
If a client section in the ini file does not include the Hostname entry, then this client is
not visible to the DNS Server (it has no name !). Example for a DNS configuration:
[General]
[DNS-Settings]
EnableDNS=1 ; if not set or set to 0, then DNS is not enabled
FORWARD=192.168.2.1 ; if set, then all requests that can not be fulfilled are forwarded to this address
DEFAULTIPADDR=192.168.10.1 ; if set, then all requests from not configured clients get this IP Address as an answer
[General]
DOMAINNAME=mydomain.local
...
Please note the DOMAINNAME in the example above. This really has to be stored in the [General] section (not [General_x]) and specifies the domain name suffix for the DNS requests. If a client is configured with hostname=linux_box_1, then linux_box_1 and linux_box_1.mydomain.local are both valid names for the client machine. EnableDNS is self explenatory, I guess.
The FORWARD setting defines one external DNS server that gets all the requests that the integrated DNS server can not answer. This feature is fairly rudimentary and works only with UDP.
The DEFAULTIPADDR setting is a very simple but effective security feature. If DEFAULTIPADDR is not set then the DNS server serves everybody as expected with resovled names. If it is set, then requesters with an unknown IP address get always the default ip address as an answer to all name resolution requests. The intention of this feature is to forward all unknown clients to a predefined default address (e.g. a web server with registration facility).
Multiple Server configurations
The [Servers] section is a new functionality in V1.8 and allows to virtualize the
DHCP Server. It was already a suggested procedure to run the DHCP Server executable
multiple times with seperate ini files, if more than one subnet with multiple IPPOOLs
each need to be supported. This was not very user friendly and didn't work for service
installations. With the [Servers] settings this is now an integrated functionality.
Here is an example on how the dhcpsrv.ini file looks like in this case:
[Settings]
InstallAsService=2 ; run as application
ShowBalloonMessages=1
NotifyTimeout=10000 ; delay after network changes detected in milliseconds
[Servers]
SERVER_1=dhcp1.ini
SERVER_2=dhcp2.ini
Two "virtual" DHCP Server instances are created with their own ini-file. All the sections and configurations can be specified in the dhcp1.ini or dhcp2.ini as usual. The settings and databases are kept seperately and behave as if two instances of the dhcpsr.exe would have been started with a dedicated ini file for each of them. The only [Settings] that are not "virtualized" are the ones shown in the example above: InstallAsService, ShowBalloonMessages and NotifyTimeout. They can not be "virtualized", because they really define the behavior of the executable process (e.g. installation or icon in the tray).
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Please be aware that all IP
addresses specified in the examples above need to be adopted to your
particular network setup. See the complete INI file reference for all
other configuration options here: INI
file reference .
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