User's Manual

UTT Technologies Chapter 7 Advanced Setup
http://www.uttglobal.com Page 156
7.8.2.1 Introduction to DHCP Server
When acting as a DHCP server, the Device can allocate network addresses and deliver
other TCP/IP configuration parameters (such as gateway IP address, DNS server IP
address, WINS server IP address, etc.) to the LAN hosts.
7.8.2.1.1 Address Conflict Detection Method
In order to prevent the DHCP server from assigning duplicate addresses that cause the
address conflict, the DHCP server should probe the address before assigning an address
to a DHCP client. The device supports two address detection methods: ARP and ICMP.
ARP is the system default method which is enabled forever and is not configurable. ICMP
method is configurable, and can be disabled.
Ɣ ARP Method: Before assigning an address to a DHCP client, DHCP will send ARP
packets to the address to detect whether it is already in use firstly. After sending two
ARP packets in succession, if no response is received, the DHCP server assumes
that the address is free. Else, the DHCP server assumes that the address is in use,
and will try another address and so on, until it finds a free address.
Ɣ ICMP Method: Once passed the ARP detection, the address needs to be detected
further by ICMP. The DHCP server will send ICMP ECHO REQUEST packets (one
packet at a time) to detect if it is already in use. After sending the specified maximum
number of ICMP packets in succession, if no response is received, the DHCP server
assumes that the address is free and assigns the address to the requesting client.
Else, the DHCP server assumes that the address is in use, and will try another
address and so on, until it finds a free address and assigns it to the client.
The maximum number of ICMP ECHO REQUEST packets is specified by the
parameter ICMP Ping Packets, and the maximum amount of time the DHCP server
waits for a ping reply packet is specified by the parameter
ICMP Ping Timeout. By
default, the value of ICMP Ping Packets is 2, and the value of DHCP Ping Timeout¶s
value is 500 milliseconds. If you want to disable the ICMP detection, please set the
DHCP Ping Packets to 0
.
7.8.2.1.2 DHCP Address Pool
The DHCP server assigns an IP address to a requesting client from a DHCP address pool,
which also can be configured to provide other TCP/IP configuration parameters to the
client, such as the DNS Server, gateway IP address, etc. The Device supports multiple
address pools, so you can easily define multiple subnets in the LAN. Before configuring an
address pool, you should specify a physical interface to which the pool is bound.