How The Mss Dhcp Server Works - D-Link DWS-1008 - AirPremier MobileLAN Switch Product Manual

How the MSS DHCP Server Works

When MSS 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 MSS finds an address that is not in use. MSS 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, MSS
ignores the DHCP Discover and generates a log message.
If the client does not respond to the DHCP Offer from the MSS DHCP server within 2 minutes, the offer
becomes invalid and MSS 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 MSS 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. If this option is not set with the set interface dhcp-server
command's dns-domain option, the MSS DHCP server uses the value set by the set ip
dns domain command.
• Option 3—Default Router. If this option is not set with the set interface dhcp-server
command's default-router option, the MSS DHCP server can use the value set by the set
ip route command. A default route configured by set ip route can be used if the route is
in the DHCP client's subnet. Otherwise, the MSS DHCP server does not specify a router
address.
• Option 6—Domain Name Servers. If these options are not set with the set interface dhcp-
server command's primary-dns and secondary-dns options, the MSS DHCP server uses
the values set by the set ip dns server command.
D-Link DWS-1008 User Manual 0