I am currently working on a project to set up a Pi 3 to serve DHCP leases to devices that connect to an isolated local network to configure them. In the process I have somehow managed to render eth0 unable to bind any IPv4 address on two separate Pi's. All other I/O remains unaffected, including Wi-Fi. In both cases I had dnsmasq installed and the problem presented itself after adjusting its config file and setting a static IP for the eth0 interface.
The first Pi was using a static IP set in /etc/dhcpcd.conf and a minimal set of options enabled in dnsmasq. The second one to fail (two weeks later) had dhcpcd disabled in favor of using /etc/network/interfaces and bridging rules between wlan0 and eth0 set using iptables. I also had more options set in dnsmasq on the second device to facilitate this.
What really confuses me, and what prompted me to ask for help here, is the fact that neither an SD card with a fresh Raspbian image nor one with a clean NOOBS installer has resolved this issue. Furthermore, either of those SD cards when placed in another fully-functional Pi 3 enable eth0 to bind to whatever IP my network's DHCP server assigns it, as one would expect with any "out-of-the-box" setup.
Let me know if you'd like more specific information, e.g. see a certain file(s) or logs, etc.
