How The Wss Software Dhcp Server Works; Configuring The Dhcp Server - Nortel 2300 Series Configuration Manual

608 Appendix D: DHCP Server

How the WSS Software DHCP Server Works

When WSS Software receives a DHCP Discover packet, the DHCP server allocates an address from the configured
range according to RFC 2131 and ARPs the address to ensure that it is not already in use. If the address is in use, the
server allocates the next address in the range, and ARPs again. The process continues until WSS Software finds an
address that is not in use. WSS Software then offers the address to the Distributed AP or client that sent the DHCP
Discover. If there are no unused addresses left in the range, WSS Software ignores the DHCP Discover and generates a
log message.
If the client does not respond to the DHCP Offer from the WSS Software DHCP server within 2 minutes, the offer
becomes invalid and WSS Software returns the address to the pool.
The siaddr value in the DHCP exchanges is the IP address of the VLAN. The yiaddr value is an unused address within
the range the server is allowed to use.
In addition to an IP address, the Offer message from the WSS Software DHCP server also contains the following
options:
• Option 54—Server Identifier, which has the same value as siaddr.
• Option 51—Address Lease, which is 12 hours and cannot be configured.
• Option 1—Subnet Mask of the VLAN's IP interface.
• Option 15—Domain Name, which is the default domain name configured on the switch. If the default domain name
is not configured, this option is blank.
• Option 3—Router. If the IP route table contains a default route with an address in the subnet configured on the
VLAN, then the server specifies this address. Otherwise, the server does not specify a router address.
• Option 6—Domain Name Server, which is a list of the DNS server IP addresses configured on the switch. If no
DNS servers are configured on the switch, this option is blank.

Configuring the DHCP Server

You can configure the DHCP server on an individual VLAN basis. To configure the server, use the following command:
set interface vlan-id ip dhcp-server [enable | disable] [start ip-addr1 stop ip-addr2]
The vlan-id can be the VLAN name or number.
The start ip-addr1 and stop ip-addr2 options specify the beginning and ending addresses of the address range (also
called the address pool). By default, all addresses except the host address of the VLAN, the network broadcast address,
and the subnet broadcast address are included in the range. If you specify the range, the start address must be lower than
the stop address, and all addresses must be in the same subnet. The IP interface of the VLAN must be within the same
subnet but is not required to be within the range.
The following command enables the DHCP server on VLAN red-vlan to serve addresses from the 192.168.1.5 to
192.168.1.25 range:
23x0# set interface red-vlan ip dhcp-server enable start 192.168.1.5 stop 192.168.1.25
success: change accepted.
To remove all IP information from a VLAN, including the DHCP client and user-configured DHCP server, use the
following command:
320657-A