The lwIP stack provides a basic DNS client (introduced in 1.3.0) to allow other applications to resolve host names to addresses using the DNS (Domain Name System) protocol. LWIP_DNS must be #defined in lwipopts.h to a nonzero value to enable DNS support in your lwIP platform. if DHCP is used in conjunction with the lwIP DNS client, DNS will automatically be configured to use the offered DNS server (if the DHCP server offers one).