Assigning multiple IPs in the same network to an interface

[Andrew Boyer]

On Feb 18, 2012, at 5:39 AM, Damien Fleuriot wrote:

> On 2/16/12 3:39 PM, Andrew Boyer wrote:
>> 
>> On Feb 16, 2012, at 8:16 AM, Damien Fleuriot wrote:
>> 
>>> On 2/16/12 8:08 AM, M. V. wrote:
>>>> hi everybody,
>>>> 
>>>> i have a problem with setting multiple IPs in the same network in FreeBSD:
>>>> 
>>>> - suppose I assign two new IP addresses in the same network to eth0 with ifconfig:
>>>> #ifconfig eth0 add 192.168.10.1/24
>>>> #ifconfig eth0 add 192.168.10.2/24
>>>> 
>>>> - everything works fine and the output of "netstat -r" is like what it should be:
>>>> #netstat -r
>>>> ....
>>>> 192.168.10.0   eth0
>>>> 192.168.10.1    lo0
>>>> 192.168.10.2    lo0
>>>> ...
>>>> 
>>>> - but now if I delete first IP address, connection to 192.168.10.0 network will be gone. and in output of "netstat -r" the route to 192.168.10.0 (via eth0) is gone:
>>>> #ifconfig eth0 delete 192.168.10.1
>>>> 
>>>> #netstat -r
>>>> ....
>>>> 
>>>> 192.168.10.2    lo0
>>>> .....
>>>> 
>>>> - am i missing something here? shouldn't the route to the network remain in routing table (because we still have 192.168.10.2 assigned to interface)?
>>>> 
>>>> Thanks.
>>>> 
>>> 
>>> You shouldn't assign your secondary IP with a /24 mask, use /32.
>>> 
>>> You'll run into problems otherwise.
>>> 
>>> As a rule of thumb, your aliases = /32
>>> 
>> 
>> M.V. -
>> What you are doing should work fine.  There were a handful of routing table bugs fixed in the last few months that corrected this behavior.  The last two were just merged to stable/8 yesterday.  What release are you running?  
>> 
>> -Andrew
>> 
> 
> This is of interest to me.
> 
> Do these fixes allow one to use say /24 aliases instead of /32 without
> running into problems ?
> 


Sorry for the long delay.  I'm not aware of any restriction on how many IPs or subnets you can install, as long as the subnets don't conflict.

I haven't tried IPv6, though...

-Andrew

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Andrew Boyer	aboyer at averesystems.com