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Old 05-17-2018, 12:28 AM   #1
ghhbak
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Extract dhcp option from dhcp ack packet in udhcpc


Hi - I'm using udhcpc which comes with busybox 1.23.2 to support networking on my embedded board. I'm able to obtain dynamic IP address from a DHCP server.

The script /lib/netifd/dhcp.script is run and within it the setup_interface function. Can someone help me understand how to collect and access the TFTP server address value (by using a script variable) which comes in the DHCP ack packet as option 150?
 
Old 05-17-2018, 05:20 AM   #2
michaelk
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There were some recent changes to udhcpc that is supposed to automatically create environment variables for known simple options. I have not examined to see if would work for option 150. Otherwise as far as I know you need to add the option to the options.c file and recompile.

https://git.busybox.net/busybox/

https://git.busybox.net/busybox/plai...c?h=1_9_stable
https://udhcp.busybox.net/README.udhcpc
 
Old 05-17-2018, 09:03 PM   #3
ghhbak
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Thanks for your response. I'm on version 1.23.2 as mentioned earlier, and there is no longer an options.c file. The documentation is outdated for a long time.
 
Old 05-18-2018, 02:28 AM   #4
ghhbak
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SOLVED

I finally figured out what is to be done. First, need to add a new macro in the list of option codes in common.h. I added it as '#define DHCP_OPTION_150 0x96'. Next, in dhcpc.c, a small code block needs to be added in udhcpc_main() and under the code block for DHCPACK, to extract the IP address:
temp = udhcp_get_option(&packet, DHCP_OPTION_150);
if (!temp) {
bb_error_msg("error: couldn't get opt 150");
} else {
uint32_t tftp_ip;
move_from_unaligned32(tftp_ip, temp);
tftp_ip = ntohl(tftp_ip);
}
 
  


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