alias netmask bug?

[Evren Yurtesen]

Jeremy Chadwick wrote:
> On Tue, Jul 24, 2007 at 03:34:54AM +0300, Evren Yurtesen wrote:
>>  I remember from earlier versions of FreeBSD that it had a restriction about 
>>  alias IP netmasks (somewhere in 3.x,4.x days)...
>>
>>  as explained here:
>>  http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/configtuning-virtual-hosts.html
>>
>>  However I tried on the loopback interface to add a 2nd IP with the same 
>>  netmask as the original IP and it accepts it fine. (on 6.2)
>>
>>  lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
>>          inet 127.0.0.1 netmask 0xff000000
>>          inet 127.0.0.2 netmask 0xff000000
>>
>>  Is FreeBSD allowing this a bug or ???
> 
> It's not a bug.  Why did you disregard the instructions, though?

I didnt disregard the instructions. I read somebody suggesting not using 
255.255.255.255 in some forum. Then I tried it out and FreeBSD accepted the 
netmask for the alias IP.

Why does FreeBSD accept such netmask which can cause problems when earlier it 
was rejecting it?

>>  If this is not a bug. What happens if an interface which is connecting to 
>>  the machine has 2 IP addresses with same netmask which is not 
>>  255.255.255.255? Does FreeBSD use each IP randomly?
> 
> Don't know, but my guess is no, it probably does not use "each IP
> randomly", and I cannot even fathom the network breakage that would
> ensue as a result of such.

I understand, I will try to test that sometime to see what FreeBSD does in this 
kind of situation.

However, it might be nice if ifconfig did not allow this kind of wrong setting.

Thanks,
Evren