Desired behaviour of "ifconfig -alias"

JoaoBR joao at
Mon Feb 12 17:27:37 UTC 2007

On Monday 12 February 2007 12:26, Oliver Fromme wrote:
> JoaoBR <joao at> wrote:
>  > "ifconfig nic -alias" is obviously a wired and confusing behaviour
> It might be confusing to you.  Personally I think that the
> current behaviour isn't that far off.

the question is not you or me, I guess that you are like me perfectly capable 
of working around messed things. But that does not make it being right or 

> First you need to be aware that there is no distinction
> between a primary IP and alias IPs (such a distinction
> existed historically, but it's gone).  All of the IPs on
> an interface are equal, just like hardlinks on a file.

I said this in shorter words in my post but it is not the point at all. 

> The "-alias" parameter simply removes an address from an

man page tells us that it removes THE specified address ... not AN address

> interface.  The term "alias" should really be avoided
> because it is misleading.  You can use "delete" or "remove"
> which do the same thing.  I think "-alias" should really
> be regarded to exist for backwards compatibility only.
> Personally I always use "delete".

it is not misleading and it is a perfect term. With alias you add secondary 
addresses to an interface. Like secondary is probably the better word, as 
cisco does, but what we have is alias and that is ok. It could be any other 
word so long as it works as it should. (We do have "add" also I remember.)

also don't forget the following, alias is a perfect and usual term, then when 
I can add an IP address with the alias cmd then -alias should remove it.

I know that I can add the first IP also with alias but that is not the usual 

 Also do not forget that the usual way since ever is ifconfig_nic_alias0 to 
add one. So this thing is confusing.

> If no IP address is specified, then it's not completely
> nonsensical to remove the first address.  In fact I've
> used that short-cut to quickly remove the only address
> from an interface.  I've used "ifconfig xyz0 delete"
> quite a lot.

the man page tells us that -alias removes *the* specified address and not the 
first, also the man page does not say that there is any further action when 
*no* IP address specified

delete is according to the man page another word for -alias, that means, using 
grammatical logic that -alias is the main command, then according to the man 
page there is no other command as "-alias *IP*" to remove an IP address 
and -alias only should not remove anything

>  > then already beeing here there is more, ifconfig nic alias does not
>  > return anything at all
> That's the same as "ifconfig nic add".  If you don't tell
> it anything to add, then it won't add anything, of course.
> Remember that UNIX always tries to do exactly what you
> tell it to dao.  ;-)

you see, now you apply logic because you want to and when not not ... ;)

to let it more clear what I mean, you say: "you don't tell it anything to add" 
so why the heck "ifconfig nic -alias" should remove one if I do not tell so?

>  > and ifconfig nic -alias on a nic w/o ip returns "can't assign
>  > requested address" ...
> That error corresponds to EADDRNOTAVAIL, which is the
> correct errno to return, because there's no address left
> on the interface.  However, I agree that the message is
> a bit confusing to the unfamiliar.

at least one agreement here :)



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