alias netmask bug?

[Julian Elischer]

Evren Yurtesen wrote:
> 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?

I'm not sure but it is possible that lo0 is treated more like a P2P
interface in which case the netmask is not used in routing decisions.

>>
>> 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
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