====== 12c Grid Infrastructure fails to configure cluster ======
Credit for solution goes to Vitaly Agapov: [[http://softsettings.com/oracle-12c-и-prif-15-invalid-format-for-subnet/]] .
But this one is in english! :-D

When installing 12c GRID, I encountered strange thing in root.sh script. The script failed with:
<code>
CRS-6024: Completed start of Oracle Cluster Ready Services-managed resources
CRS-4123: Oracle High Availability Services has been started.
2016/03/03 15:07:34 CLSRSC-343: Successfully started Oracle Clusterware stack
PRKO-2190 : VIP exists for node db1, VIP name db1-vip.local
2016/03/03 15:07:45 CLSRSC-180: An error occurred while executing the command '/oracle/12.1.0/grid/bin/oifcfg setif -global enp0s3/172.31.255.0:public enp0s8/172.31.254.0:cluster_interconnect' (error code 1)
2016/03/03 15:07:46 CLSRSC-287: FirstNode configuration failed
Died at /oracle/12.1.0/grid/crs/install/crsinstall.pm line 2398.
The command '/oracle/12.1.0/grid/perl/bin/perl -I/oracle/12.1.0/grid/perl/lib -I/oracle/12.1.0/grid/crs/install /oracle/12.1.0/grid/crs/install/rootcrs.pl  -auto -lang=en_US.utf8' execution failed
</code>

Installation log is not really helpful. I diagnosed other clusterware logs - because at the moment of this failure, clusterware is alive but not yet fully operational. But it is alive, so it means it spits out a ton of other logs! In one of them I found:
<code>
PRIF-15: INVALID FORMAT FOR SUBNET
</code>

If you try to google it, you get plenty of results about 11g installation, which do not really help. **Turns out, this is actually a bug in 12.1.0.2. Clusterware fails to configure if IP address contains octet with value 255.** Yeah, I was installing in subnet xxx.xxx.255.xxx/24 so it was my case. Oracle released a patch 19777496 which solves this "failure occurs when you install clustering software version 12.1.0.2 on some valid IP addresses".

In the original post there is also a howto on installing 12.1.0.2 in such setup. In a nutshell, it is patching GRID after installation but before running root.sh. I'm not a big fan of this approach so for me the solution is simpler - use different subnet. ;-)