I'm working with third-party software that talks to ethernet-connected cameras. Between Yosemite and El Capitan this software lost its ability to find cameras.
I also found that "ping 255.255.255.255" no longer works- I use this (with WiFi turned off) to get IP addresses without knowing them beforehand- and I suspect the two problems are related. The message from ping is "no route to host", and it times out.
If I use the connected device's IP address in the ping command instead of 255.255.255.255 the device does send a reply.
The ping problem is easily reproduced by connecting two Macs, one with an older OS X, with an ethernet cable. The ping 255.255.255.255 works in one direction only. When I use Wireshark I see both messages, outgoing and incoming, on the older OS but neither under 10.11.
I've tried several things, including tossing system config files, resetting the SMC and PRAM (it happens on a Mac Pro and an iMac), booting in safe mode (as myself and as "Noprivs"), and using a beta of 10.11.1.
I know that Apple made some changes related to ipv4 vs. ipv6, but I wouldn't know if this is related.
Has anyone seen a similar problem? I'm seeking a solution but sympathy might help.
Thanks-
Scott