Documentation for Kerio WinRoute

DHCP server

The DHCP protocol (Dynamic Host Configuration Protocol) is used for easy TCP/IP configuration of hosts within the network. The DHCP server selects appropriate configuration parameters (IP address with appropriate subnet mask and other optional parameters, such as IP address of the default gateway, addresses of DNS servers, domain name, etc.) for the client stations.

The DHCP server assigns clients IP addresses within a predefined scope for a certain period (lease time). If an IP address is to be kept, the client must request an extension on the period of time before the lease expires. If the client has not required an extension on the lease time, the IP address is considered free and can be assigned to another client.

So called reservations can be also defined on the DHCP server certain clients will have their own IP addresses reserved. Addresses can be reserved for a hardware address (MAC) or a host name. These clients will have fixed IP address. These addresses are configured automatically.

Using DHCP brings two main benefits. First, the administration is much easier than with the other protocols as all settings may be done at the server (it is not necessary to configure individual workstations). Second, many network conflicts are eliminated (i.e. one IP address cannot be assigned to more than one workstation, etc.).

DHCP Server Configuration

To configure the DHCP server in WinRoute go to Configuration / DHCP Server. Here you can define IP scopes, reservations or optional parameters, and view information about occupied IP addresses or statistics of the DHCP server.

The DHCP server can be enabled/disabled using the DHCP Server enabled option (at the top). Configuration can be modified even when the DHCP server is disabled.

Definition of Scopes and Reservations

To define scopes including optional parameters and to reserve IP addresses for selected clients go to the Scopes dialog. The tab includes two parts in one address scopes and in the other reservations are defined:

In the Item column, you can find subnets where scopes of IP addresses are defined. The IP subnet can be either ticked to activate the scope or unticked to make the scope inactive (scopes can be temporarily switched off without deleting and adding again). Each subnet includes also a list of reservations of IP addresses that are defined in it.

In the Default options item (the first item in the table) you can set default parameters for DHCP server.

Time for which an IP address is assigned to clients. This IP address will be automatically considered free by expiration of this time (it can be assigned to another client) unless the client requests lease time extension or the address release.

DNS server

Any DNS server (or multiple DNS servers separated by semicolons) can be defined. We recommend you to use DNS Forwarder in WinRoute as the primary server (first in the list) IP address of the WinRoute host. DNS Forwarder can cooperate with DHCP server (see chapter  DNS Forwarder ) so that it will always use correct IP addresses to response to requests on local host names.

WINS server

IP address of the WINS server.

Domain

Local Internet domain. Do not specify this parameter if there is no local domain.

Advanced

Click on the Advanced button to open the dialog which includes list of all optional parameters supported by DHCP protocol (including the ones described above).You can add any parameter supported by DHCP protocol and set its value.

Default parameters are automatically matched with address scopes unless configuration of a particular scope is defined (the Address Scope/Options dialog). The same rule is applied on scopes and reservations (parameters defined for a certain address scope are used for the other reservations unless parameters are defined for a specific reservation). Weight of individual parameters corresponds with their position in the tree hierarchy.

Select the Add / Scope option to view the dialog for address scope definition.

Note: Only one scope can be defined for each subnet.

Comment on the new address scope (just as information for WinRoute administrator).

First address, Last address

First and last address of the new scope.

Note: If possible, we recommend you to define the scope larger than it would be defined for the real number of users within the subnet.

Mask

Mask of the appropriate subnet. It is assigned to clients together with the IP address.

Note: The Kerio Administration Console application monitors whether first and last address belong to the subnet defined by the mask. If this requirement is not met, an error will be reported after the confirmation with the OK button.

Lease time

Time period during which the client can use the IP address. Unless the client has requested extension of the lease time during this period, the IP address is considered free and can be assigned to another client.

Exclusions

WinRoute enables the administrator to define only one scope in within each subnet. To create more individual scopes, follow these instructions:

• create address scope covering all desired scopes

• define so called exclusions that will not be assigned

Example: In 192.168.1.0 subnet you intend to create two scopes: from 192.168.1.10 to 192.168.1.49 and from 192.168.1.61 to 192.168.1.100. Addresses from 192.168.1.50 to 192.168.1.60 will be left free and can be used for other purposes.

Create the scope from 192.168.1.10 to 192.168.1.100 and click on the Exclusions button to define the scope from 192.168.1.50 to 192.168.1.60. These addresses will not be assigned by the DHCP server.

In the Address Scope dialog, basic DHCP parameters of the addresses assigned to clients can be defined:

• Default Gateway IP address of the router that will be used as the default gateway for the subnet from which IP addresses are assigned.

• DNS server any DNS server (or more DNS servers separated with semicolons). We recommend you to use the DNS Forwarder in WinRoute as the primary DNS server ( IP address of the WinRoute host). The reason is that the DNS Forwarder can cooperate with the DHCP server (see chapter  DNS Forwarder ) and it will always respond to requests on local host names with the correct IP address.

• WINS name server In networks with multiple routers it is sometimes necessary to use a WINS (Windows Internet Naming Service) to resolve local NetBIOS computer names.

• Domain local internet domain. Do not define this parameter unless there is a local domain.

Advanced

Click on this button to open a dialog with a complete list of advanced parameters supported by DHCP (including the four mentioned above). Any parameter supported by DHCP can be added and its value can be set within this dialog. This dialog is also a part of the Address Scopes tab.

To view configured DHCP parameters and their values within appropriate IP scopes see the right column in the Address Scope tab.

Note: Simple DHCP server statistics are displayed at the right top of the Address Scope tab. Each scope is described with the following items:

• total number of addresses within this scope

• number and percentage proportion of leases

• number and percentage proportion of free addresses

Lease Reservations

DHCP server enables the administrator to book an IP address for any host. To make the reservation click on the Add / Reservations button in the Scopes folder.

Any IP address included in a defined subnet can be reserved.

IP addresses can be reserved for:

• hardware (MAC) address of the host it is defined by hexadecimal numbers separated by colons, i.e.

  00:bc:a5:f2:1e:50

  or by dashes for example:

  00-bc-a5-f2-1e-50

  The MAC address of a network adapter can be detected with operating system tools (i.e. with the ipconfig command) or with a special application provided by the network adapter manufacturer.

• host name DHCP requests of most DHCP clients include host names (i.e. all Windows operating systems), or the client can be set to send a host name (i.e. Linux operating system).

Leases

IP scopes can be viewed in the Leases tab. These scopes are displayed in the form of trees. All current leases within the appropriate subnet are displayed in these trees.

Note: Icon color represents address status (see below). Icons marked with R represent reserved addresses.

Columns in this section contain the following information:

• Leased Address leased IP address

• Lease Expiration date and time specifying expiration of the appropriate lease

• MAC Address hardware address of the host that the IP address is assigned to (including name of the network adapter manufacturer).

• Hostname name of the host that the IP address is assigned to (only if the DHCP client at this host sends it to the DHCP server)

• Status status of the appropriate IP address; Leased (leased addresses), Expired (addresses with expired lease the client has not asked for the lease to be extended yet), Declined (the lease was declined by the client) or Released (the address has been released by the client).

  Notes:

  1. Data about expired and released addresses are kept by the DHCP server and can be used later if the same client demands a lease.

  2. Declined addresses are handled according to the settings in the Options tab (see below).

The following columns are hidden by default:

• Last Request Time date and time when the recent request for a lease or lease extension was sent by a client

• Lease Remaining Time time remaining until the appropriate Lease Expiration

Use the Release button to release a selected IP address immediately (independently of its status). Released addresses are considered free and can be assigned to other clients immediately.

Click on the Reserve button to reserve a selected (dynamically assigned) IP address based on the MAC address or name of the host that the address is currently assigned to. The Scopes tab with a dialog where the appropriate address can be leased will be opened automatically. All entries except for the Description item will be already defined with appropriate data. Define the Description entry and click on the OK button to assign a persistent lease for the IP address of the host to which it has been assigned dynamically.

Note: The MAC address of the host for which the IP is leased will be inserted to the lease reservation dialog automatically. To reserve an IP address for a hostname, change settings of the Reservation For and Value items.

Options

Other DHCP server parameters can be set in the Options tab.

If this option is enabled, the DHCP server will assign IP addresses (including optional parameters) also to clients of BOOTP protocol (protocol used formerly to DHCP it assigns configurations statically only, according to MAC addresses).

Windows RAS

Through this option you can enable DHCP service for RAS clients (Remote Access Service). You can also specify time when the service will be available to RAS clients (an IP address will be assigned) if the default value is not convenient.

Declined options

These options define how declined IP addresses (DHCPDECLINE report) will be handled. These addresses can be either considered released and assigned to other users if needed (the Offer immediately option) or blocked during a certain time for former clients to be able to use them (the Declined addresses can be offered after timeout option).