Technical information

Chapter 2: AT+i Commands Reference
May 31, 2008 AT+i Commands Reference Manual 2-49
DHCP Client
A DHCP client component in W24 in WLAN mode supports IP and server name acquisition from
a standard DHCP Server. The W24 device attempts to contact and acquire server names from a
DHCP server if and when its DIP (Default IP) parameter contains the special value 0.0.0.0.
When the DHCP acquisition procedure is successful, the W24's IPA (IP Address) parameter
contains the assigned IP address retrieved from the DHCP server. In addition, server names
relevant to W24 parameters are retrieved from the DHCP server, if and only if they contain empty
values at power-up (seeTable 2-2). Parameters that contain non-empty values retain those values.
In addition, DNS values retrieved from the DHCP server are retained as additional alternative
DNS addresses when DNSn contain user-defined values.
All values acquired from the DHCP server are not retained as nonvolatile values. New values
shall be acquired during the next DHCP session, which will be activated during the next W24
power-up, following a soft or hard reset or after the DHCP lease expires.
The DHCP client has two associated points in time when the DHCP server is contacted for
additional negotiations. At T1 (usually after half the original lease period), W24 attempts to
renew the lease period. If the renewal procedure fails, at T2 (usually after 7/8 the original lease
period) W24 attempts to re-negotiate the lease. If the procedures at T1 and T2 fail and the lease
expires, W24 continuously tries to locate a DHCP server for re-negotiation. When this is the case,
W24 stores 0.0.0.0 in the IPA parameter and cannot communicate on the WLAN until a DHCP
server is found and IP and server names are acquired.
Table 2-2: Server Names Acquired from DHCP Server
Parameter
Name
Function Empty Value
IPG Gateway 0.0.0.0
SNET Subnet Mask 0.0.0.0
DNS1 Primary Domain Name Server 0.0.0.0
DNS2 Secondary Domain Name Server 0.0.0.0
SMTP Email Send Server '' (Empty String)
POP3 Email Receive Server '' (Empty String)