>>> What you're supposed to have in addition to the index is a way to
>>> use it to query for all the other state associated with the
>>> interface.  Then the index can become the canonical way for software
>>> to refer to an interface, leaving the pretty ascii name for humans
>>> to use.
>> well...if there was a kernel interface that could make use of said
>> numbers...that'd be cool.  as it is, they're not much good to me.  i
>> used it in the kernel once, though.  there it was good.
>
>This perhaps has something to do with your attempts to manipulate ARP
>entries failing; looking at the code for the program that deals with
>them, I find that when creating ARP entries, I use if_index values to
>name interfaces there.

i just looked at an pulled out the code that pppd uses to install
proxy arp entries.  it doesn't use if_index numbers in any way that's
obvious.

>I don't know offhand of any other interface that uses index values to
>name interfaces.  My code never goes the other way; it looks up the
>index values for the interfaces it cares about, but never has occasion
>to map from index values to the interface in any other sense.

i was just thinking it might be useful.  somewhere.  kinda like the
way fhopen(3) is useful somewhere.

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