WeOSDHCP Server HowTo
Introduction
Imagine a network topology with a number of devices connected to a router on two different VLANs. To avoid configuring static addresses for all devices on the network, we configure the router to also act as a DHCP server. We also want to inform the devices that the router is the default gateway and DNS server.
In some cases, predetermined roles on the network of certain hosts are preferred. For example, a given port on a switch, or a client which sends a certain hostname should always get a static IP address. For such cases the DHCP server can be configured with Static Host Entires that are individually configured. These entries are configured to be provided to host that meets the matching requirement of the entry, this can be either a Client Id, MAC address or DHCP Option 82 (switch port).
|
.--.-.
( ( )__
(_, \ ) ,_) Internet/Intranet
'-'--`--'
|
.---+----.
vlan1 | DHCP | vlan2
+-----+ Server +-----+
| .1| |.1 |
| '--------' |
192.168.1.0/24 | | 192.168.2.0/24
----+----------+----+--- ---+----+----------+----
| | | |
.-+--. .-+--. .-+--. .-+--.
| H1 | | H2 | | H3 | | H4 |
'----' '----' '----' '----'
Figure 1: Example network with two LANs
Configuration
- DHCP Server
-
The DHCP Server is with two different subnet definitions, each with their own address pool, in order to distribute addresses to both VLANs.
Interface Configuration
- VLAN1
- Address: 192.168.1.1
- VLAN2
- Address: 192.168.2.1
DHCP Server Configuration
- Subnet 1
-
- Pool: 192.168.1.100/24 - 192.168.1.150/24
- lease time: 1 hour
- Gateway: 192.168.1.1
- Name-server: 192.168.1.1
- Subnet 2
-
- Pool: 192.168.2.100/24 - 192.168.2.150/24
- lease time: 1 hour
- Gateway: 192.168.2.1
- Name-server: 192.168.2.1
Address Pools
Enter the DHCP Server configuration Context:
example:/#> configure example:/config/#> dhcp-server example:/config/dhcp-server/#>
Configure the dynamic pool for subnet 192.168.1.0:
example:/config/dhcp-server/#> subnet 192.168.1.0/24 example:/config/dhcp-server/subnet-192.168.1.0/#> pool 192.168.1.100 192.168.1.149 example:/config/dhcp-server/subnet-192.168.1.0/#> lease-time 3600 example:/config/dhcp-server/subnet-192.168.1.0/#> gateway 192.168.1.1 example:/config/dhcp-server/subnet-192.168.1.0/#> name-server 192.168.1.1 example:/config/dhcp-server/subnet-192.168.1.0/#> end example:/config/dhcp-server/#>
Configure the dynamic pool for subnet 192.168.2.0:
example:/config/dhcp-server/#> subnet 192.168.2.0/24 example:/config/dhcp-server/subnet-192.168.2.0/#> pool 192.168.2.100 192.168.2.149 example:/config/dhcp-server/subnet-192.168.2.0/#> lease-time 3600 example:/config/dhcp-server/subnet-192.168.2.0/#> gateway 192.168.2.1 example:/config/dhcp-server/subnet-192.168.2.0/#> name-server 192.168.2.1 example:/config/dhcp-server/subnet-192.168.2.0/#> end example:/config/dhcp-server/#> leave example:/#>
When we enter the configuration for the specific a few different variables are configured:
-
First the
poolof available addresses are configured to serve up to 50 hosts on that subnet (.100 - .149). -
The
lease-timeis configured so that each address are supplied with a validity of one hour (3600 seconds). When that time has elapsed any host that wants to retain its given address will need to consult the server again to renew it. -
Both a
gatewayandname-serverare defined to be accessible on the DHCP server it self, since in this case it also serves as the router for the two local networks.
The server is now configured to serve two different subnets, all these addresses will be handled dynamically so no additional actions should be needed.
Static Leases
In this example we want to provide a specific configuration for H3 based on its MAC address. We also want to provide a Specific address on the subnet 192.168.1.0/24 for any host with a specific Client Id.
Enter the DHCP Server configuration Context:
example:/#> configure example:/config/#> dhcp-server example:/config/dhcp-server/#>
Configure host 1:
example:/config/dhcp-server/#> host 1 example:/config/dhcp-server/host-1/#> match client string some_clientid_string example:/config/dhcp-server/host-1/#> address 192.168.1.10 example:/config/dhcp-server/host-1/#> lease-time 10000 example:/config/dhcp-server/host-1/#> gateway 192.168.1.1 example:/config/dhcp-server/host-1/#> end
The host 1 static lease is configured to match on a clientid string. If a host provides
the matching Client Id it will be provided with the specific address
192.168.1.10, instead of an address from the dynamic address pool.
Configure host 2:
example:/config/dhcp-server/#> host 2 example:/config/dhcp-server/host-2/#> match mac 0c:50:e5:4f:d6:00 example:/config/dhcp-server/host-2/#> address 192.168.2.20 example:/config/dhcp-server/host-2/#> lease-time 10000 example:/config/dhcp-server/host-2/#> gateway 192.168.2.1 example:/config/dhcp-server/host-2/#> end example:/config/dhcp-server/#> leave example:/#>
The host 2 static lease is configured to match on a specifc mac
address. Any host associated with the matching MAC will be provided the
specific address 192.168.2.20, and not another address from the
dynamic pool of addresses.
Status
In order to verify if any DHCP leases are handed out to hosts on the subnet:
example:/#> show dhcp-server LEASE TIME MAC ADDRESS CLIENT ID IP ADDRESS HOSTNAME 3600 0c:50:e5:8c:52:00 01:0c:50:e5:8c:52:00 192.168.1.136 H1 10000 0c:50:e5:7c:45:00 01:0c:50:e5:7c:45:00 192.168.1.10 H2 10000 0c:50:e5:4f:d6:00 01:0c:50:e5:4f:d6:00 192.168.2.20 H3 3600 0c:50:e5:33:a6:00 01:0c:50:e5:33:a6:00 192.168.2.121 H4
This shows the specific IP Addresses that have been handed out, and to which host (MAC Address) they have been provided for. This list should show all addresses that the server have provided, therefore this command is useful when debugging address distribution for your network.