Network Interface starts without IPV4

Question

When I boot some RHEL 6.5 server, the NIC shows an IPV6 address but no IPV4 on ifconfig

However, if I ifdown + ifup it, it gets its IPV4 address (via DHCP).
For clarity, is is enabled on boot via ifcfg-em1 ONBOOT=yes

What am I doing wrong to miss the IPV4 address on boot?

Edit

/etc/sysconfig/network-scripts/ifcfg-em1 content:

DEVICE=em1
HWADDR=90:B1:1C:71:46:77
TYPE=Ethernet
UUID=46136e95-f76b-4443-a63c-911466f8bd52
ONBOOT=yes
NM_CONTROLLED=yes
BOOTPROTO=dhcp

ifconfig output after reboot

em1       Link encap:Ethernet  HWaddr 90:B1:1C:71:46:77  
          inet6 addr: fe80::92b1:1cff:fe71:4677/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:14696 errors:0 dropped:0 overruns:0 frame:0
          TX packets:329 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:1517399 (1.4 MiB)  TX bytes:44306 (43.2 KiB)
          Interrupt:20 Memory:ef400000-ef420000 

ifconfig output after ifdown / ifup

em1       Link encap:Ethernet  HWaddr 90:B1:1C:71:46:77  
          inet addr:10.25.31.29  Bcast:10.25.31.255  Mask:255.255.254.0
          inet6 addr: fe80::92b1:1cff:fe71:4677/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:14696 errors:0 dropped:0 overruns:0 frame:0
          TX packets:329 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:1517399 (1.4 MiB)  TX bytes:44306 (43.2 KiB)
          Interrupt:20 Memory:ef400000-ef420000 

Edit 2
I have renamed em1 to eth0 using this guide. But it doesn't fix the problem.

Answer 1

The solution was to remove persisted rules, after making sure eth0 had caught and ipv4 address. Hence the sequence

ifup eth0
rm /etc/udev/rules.d/70-persistent-net.rules
reboot

I am not sure what got persisted nor why, but it worked right away