Normally this is not necessary. However, it is necessary if you run the atftp server on a Linux box and your tftp clients cause the daemon to listen on the broadcast address (255.255.255.255). In most cases it does not happen, but some clients, such as Sparcstation 20, do it.
The Linux kernel (as of the 2.4 series) ignores network packets directed to a local broadcast address. Unless you apply the patch, you're out of luck, because there aren't any kernel options to fix it, and if you're savvy enough to add an SO_BROADCAST socket option to the code, you'll find that Linux ignores that, too. So this patch allows the tftpd service to respond to clients that would otherwise be unable to communicate with your server.
The clients weren't booting tftp, so through a variety of trial-and-error, looking at logs and using tcpdump, I located the problem. I tried to find a kernel option that would fix it, tried to locate something in /proc/sys, and also tried to use SO_BROADCAST, but nothing worked. So I wrote the patch.
This was two years ago, and it's been happy ever since.
This patch is under a BSD style license, which means you can use it, modify it, distribute it, as long as you adhere to the terms of the license, which basically state that you gotta keep the copyright notice and license text with the patch. Read the top portion of the patch for details. Download it here: ./download/atftp-0.7-listenlocal.patch. The md5 checksum is: c7f4cf5a1c21c37d2545cabb0bfca883
Real easy to use. Once you get the source patched, then set up your server something like the following:
/system/atftp/sbin/in.tftpd --listen-local --logfile /var/log/atftpd.log --verbose=6 --user tftp.tftp /tftpboot/
The exact incantation of course will vary depending on how you launch in.tftpd, from xinetd, rc.d, or whatever.
When I wrote this patch, I was the Engineering Manager for the Computer Center at New Mexico Tech (http://www.nmt.edu/tcc/). I now wear a different hat, but I still maintain this patch. I've also got another Sourceforge project: http://sftplogging.sourceforge.net. More information about me is there on the "About the Author" link.
I'm curious to hear if anyone else uses this patch other than me. If you need to talk to me, send me email: firstname.lastname@example.org.