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When I see the man page for interfaces I see the below. Has anyone seen similar behavior, I had been using Ubuntu for some time and my net-books interface name has not changed for ever.

The ifup and ifdown programs work with so-called "physical" interface names. These names are assigned to hardware by the kernel. Unfortunately it can happen that the kernel assigns different physical interface names to the same hardware at different times; for example, what was called "eth0" last time you booted is now called "eth1" and vice versa. This creates a problem if you want to configure the interfaces appropriately. A way to deal with this problem is to use mapping scripts that choose logical interface names according to the properties of the interface hardware.

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Modern Linux distributions will automatically assign permanent names to hardware. Debian's /etc/network/interfaces mechanism for interface identification and naming is uneeded in this respect.

In the network interface case, identification of previously seen interfaces is based at least on the hardware MAC address. The names are remembered in the form of udev rules; take a look at /etc/udev/rules.d/*-persistent-*.

In particular, /etc/udev/rules.d/70-persistent-net.rules stores network interface mappings. This file is auto-generated, but can be changed manually, as its header says:

# This file was automatically generated by the /lib64/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, and change only the value of the NAME= key.
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cool thnx - this file has the mapping between the mac and the interface name. just curious, look like this is a generated file. if i want to change the interface name, how do i do it? –  Praveen Sripati Sep 11 '11 at 14:38
    
# You can modify it, as long as you keep each rule on a single # line, and change only the value of the NAME= key. –  ultrasawblade Aug 21 '12 at 20:58
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