etc/udev/rules.d/z25_persistent-net.rules

を見てみると、こんなことが書いてある。

# This file was automatically generated by the /lib/udev/write_net_rules

# program run by the persistent-net-generator.rules rules file.

#

# You can modify it, as long as you keep each rule on a single line.

# PCI device 0x10de:0x054c (forcedeth)

SUBSYSTEM=="net", DRIVERS=="?*", ATTR{address}=="bc:99:50:d0:1f:00", NAME="eth0"

# PCI device 0x10de:0x054c (forcedeth)

SUBSYSTEM=="net", DRIVERS=="?*", ATTR{address}=="00:1f:d0:50:99:bc", NAME="eth1"

……なんでアドレスが2個もあるの？？