https://access.redhat.com/solutions/53031

On RHEL with version number more than 5 in order to make rule based routing work we need to set rp_filer = 2:

# echo 2 > /proc/sys/net/ipv4/conf/default/rp_filter
# echo 2 > /proc/sys/net/ipv4/conf/all/rp_filter

And to make the change persistent add to /etc/sysctl.conf:

net.ipv4.conf.default.rp_filter = 2

Reason:

RHEL6's (and RHEL7's) default setting is more strict than RHEL5's, as RHEL6 follows the Strict Reverse Path Forwarding filtering recommended in RFC 3704 - Ingress Filtering for Multihomed Networks.