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RL-ARM User's Guide (MDK v4)

RL-RTX RL-FlashFS RL-TCPnet TCP Socket Opening TCP Connection TCP Active Open TCP Passive Open Sending TCP Data Example for Sending Data Multiple TCP Connections UDP Socket Opening UDP Connection Sending UDP Data When DHCP Enabled When ARP Cache Empty Example for Sending Data IP Multicasting Multiple UDP Connections Configuring RL-TCPnet Static Configuration System Definitions Ethernet Network Interface PPP Network Interface SLIP Network Interface UDP Socket TCP Socket BSD Socket HTTP Server Telnet Server TFTP Server TFTP Client FTP Server FTP Client DNS Client SMTP Client SNMP Agent SNTP Client Error Function Runtime Configuration Library Files Using RL-TCPnet Stand Alone With RTX Kernel Event Driven Operation IP Address Assignment Ethernet Interface PPP Interface SLIP Interface Localhost Applications HTTP Server Script Language CGI Functions Ajax Support Using XML XML Example How it works SOAP Support SOAP Interface Large POST Messages Web Pages Default Page Error Pages Web on SD Card Web Update File System Interface Http Caching How it works Internal Web External Web Multi-user Authentication Using RAM File System FCARM File Converter PRINT Directive NOPRINT Directive PAGEWIDTH Directive PAGELENGTH Directive ROOT Directive Telnet Server Command Line Interface Multi-user Authentication Sending Reply Message Short Reply Long Reply Continuous Screen Update TFTP Server File System Interface TFTP Client File System Interface FTP Server File System Interface Multi-user Authentication Supported Commands FTP Client File System Interface SMTP Client SNMP Agent MIB Database MIB Interface MIB Entry MIB Table DNS Resolver Starting DNS Device Drivers Ethernet Driver Interrupt Mode Modem Driver Serial Driver Using Serial Link Cable Connection Modem Connection Windows Dial-up Add Direct Serial Link New Dial-up Connection Configure PPP Dial-up Configure SLIP Dial-up Debugging Enabling Debug Debug Level Redirecting Output Function Overview BSD Routines CGI Routines Ethernet Routines FTP Routines HTTP Routines IGMP Routines Miscellaneous Routines Modem Routines PPP Routines Serial Routines SLIP Routines SMTP Routines SNMP Routines System Functions TCP Routines Telnet Routines TFTP Routines UDP Routines RL-CAN RL-USB Example Programs Library Reference Appendix

Starting DNS

Start the DNS Resolver by calling the function get_host_by_name(). DNS Requests are routed to the DNS Server IP address of an active network interface. If you are using a PPP or SLIP interface and no ethernet interface, you must enable the Use default gateway on remote network option in the configuration.

You must also specify a callback function, which is called from the DNS Client when a DNS event occurs.

static void dns_cbfunc (U8 event, U8 *ip) {
  switch (event) {
      printf("IP Address: %d.%d.%d.%d\n",ip[0],ip[1],ip[2],ip[3]);
    case DNS_EVT_NONAME:
      printf("Host name does not exist.\n");
      printf("DNS Resolver Timeout expired, Host IP not resolved.\n");
    case DNS_EVT_ERROR:
      printf("DNS Resolver Error, check the host name, labels, etc.\n");

When the required host is found in the local DNS Cache, the callback function is called immediately with the result code DNS_EVT_SUCCESS and provides the IP address of the host to the function. In this case, no actual DNS request packet is sent to the remote DNS Server.


  • To use an Embedded DNS Client, you must enable and configure it in the configuration file.
  • You can also provide the IP address in a string format to specify the host name. The DNS Client decodes it and returns the decoded IP address to the callback function.
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