Comment 3 for bug 1307429

The difference between auto and allow-hotplug is the behaviour on boot. When a device is marked as auto, it will be tried to be activated on boot and the boot will wait for the device to come up. Following interface config

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auto lo
iface lo inet loopback
auto eth0
iface eth0 inet dhcp
auto eth1
iface eth1 inet dhcp
auto eth2
iface eth2 inet dhcp
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will cause these plymouth output:

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waiting for network configuration
waiting an additional 60 seconds for network configuration
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So allow-hotplug is not equivalent to auto and is bug which should be fixed in a SRU. Side note: allow-hotplug works on Debian.