Assigning multiple IPs in the same network to an interface

[Andrew Boyer]

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

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Andrew Boyer	aboyer at averesystems.com