I am using snort with --enable-inline to make it useful as IPS

Below is the portion of my snort.conf


# Step #5: Configure snort with config statements
#
# See the snort manual for a full set of configuration references
#
config flowbits_size: 64
#
# New global ignore_ports config option from Andy Mullican
#
# config ignore_ports: <tcp|udp> <list of ports separated by whitespace>
config ignore_ports: tcp 80
# config ignore_ports: udp 1:17 53


####################################################################

The problem is that although I have configured the file by specifying (SHOWN IN RED ABOVE) that it must not detect or log traffic of port 80 running on TCP protocol....


But the thing is that when I run snort and if I send traffic it detects and logs......

did you try restarting snort service after changing the conf file ??

root# service snortd restart

Im not sure whether its snortd, you can check the service name with this command

root# service --status-all | grep snort

You will get the name of the snort service, use this to restart the service.