Why are network interfaces not ordered correctly?

Issue

• Why are network interfaces not ordered correctly?
• In previous versions of Red Hat Enterprise Linux, ifindex values were in order with ethX names:

# cd /sys/class/net
# cat eth0/ifindex eth1/ifindex eth2/ifindex eth3/ifindex 
2
3
4
5
#

• In Red Hat Enterprise Linux 7 it is different:

# cd /sys/class/net
# cat eth0/ifindex eth1/ifindex eth2/ifindex eth3/ifindex 
4
5
2
3
# 

• The ip addr command display does not display the NIC in names order, but ifconfig does. Is it possible to have this ordered alphabetically? What is this ordered by?