Why network interfaces are not coming up at boot time in Red Hat Enterprise Linux 7.2 ?

Issue

• Network interfaces fails to load at boot time, booting logs shows below messages at the time of loading the interfaces.

Jul 28 01:57:37 HOSTNAME network[9325]: Bringing up interface bond0:  ERROR    : [/etc/sysconfig/network-scripts/ifup-eth] Device em1 does not seem to 
be present, delaying initialization.
Jul 28 01:57:37 HOSTNAME /etc/sysconfig/network-scripts/ifup-eth: Device em1 does not seem to be present, delaying initialization.
Jul 28 01:57:37 HOSTNAME network: Bringing up interface bond0:  ERROR    : [/etc/sysconfig/network-scripts/ifup-eth] Device em1 does not seem to be pre
sent, delaying initialization.
Jul 28 01:57:37 HOSTNAME network[9325]: WARN     : [/etc/sysconfig/network-scripts/ifup-eth] Unable to start slave device ifcfg-em1 for master bond0.
Jul 28 01:57:37 HOSTNAME /etc/sysconfig/network-scripts/ifup-eth: Device em1 does not seem to be present, delaying initialization.
Jul 28 01:57:37 HOSTNAME network: WARN     : [/etc/sysconfig/network-scripts/ifup-eth] Unable to start slave device ifcfg-em1 for master bond0.
Jul 28 01:57:37 HOSTNAME /etc/sysconfig/network-scripts/ifup-eth: Unable to start slave device ifcfg-em1 for master bond0.
Jul 28 01:57:37 HOSTNAME /etc/sysconfig/network-scripts/ifup-eth: Unable to start slave device ifcfg-em1 for master bond0.
Jul 28 01:57:37 HOSTNAME network[9325]: ERROR    : [/etc/sysconfig/network-scripts/ifup-eth] Device p5p2 does not seem to be present, delaying initiali
zation.
Jul 28 01:57:37 HOSTNAME network: ERROR    : [/etc/sysconfig/network-scripts/ifup-eth] Device p5p2 does not seem to be present, delaying initialization
.
Jul 28 01:57:37 HOSTNAME /etc/sysconfig/network-scripts/ifup-eth: Device p5p2 does not seem to be present, delaying initialization.
Jul 28 01:57:37 HOSTNAME /etc/sysconfig/network-scripts/ifup-eth: Device p5p2 does not seem to be present, delaying initialization.
Jul 28 01:57:37 HOSTNAME network[9325]: WARN     : [/etc/sysconfig/network-scripts/ifup-eth] Unable to start slave device ifcfg-p5p2 for master bond0.
Jul 28 01:57:37 HOSTNAME network: WARN     : [/etc/sysconfig/network-scripts/ifup-eth] Unable to start slave device ifcfg-p5p2 for master bond0.
Jul 28 01:57:37 HOSTNAME /etc/sysconfig/network-scripts/ifup-eth: Unable to start slave device ifcfg-p5p2 for master bond0.
Jul 28 01:57:37 HOSTNAME /etc/sysconfig/network-scripts/ifup-eth: Unable to start slave device ifcfg-p5p2 for master bond0.

• Once the system is booted then after restarting the network service, interfaces come up fine.