Multiple Interfaces

[Oleg Polyakov]

--- Bob <bob at starblanket.ca> wrote:
> Greets 
> 
> > I have two interfaces and the following info in rc.conf.  The 
> > first one is
> > setup properly but the second one never gets configured.
>  
> I just went through this process myself.
> 
> The word I have is that FreeBSD cannot run two NICs on
> the same subnet, which is what your included config shows.
> So try as you may it will not work. I also tested 4.7, 5.0 
> and 5.1 with similar results. 

The trick is to configure second interface with netmask 255.255.255.255.
That interface can't be default gateway. But if anything listen to that address
than it responds on that address.

You may see log messages like this:
arp: 10.13.1.2 is on fxp0 but got reply from 00:00:0c:61:2e:c0 on fxp1

To disable it run:
sysctl net.link.ether.inet.log_arp_wrong_iface=0

> Here is a snippet of an email I received on this topic:
> 
> Begin
> 
> Well, as long as I can tell, one can't have 2 ifaces on the same subnet 
> on FreeBSD. This seems to be regarded as a feature by the guys who have 
> written the code. "It's arguable that it should be done any other way, 
> since it will put questions like  what interface will be used for 
> outgoing segments to the subnet ? etc. which will require to manually  
> assign the arp table as log as you have the rest of the nodes of the 
> subnet connected throu some kind of switches or to still have all 
> outgoing connections throu a preferred interface which will require a 
> SRC (IP+MAC) addresses of the other interface and will unnecessary 
> complicated the hole thing". So the result will be a gain in the speed 
> of incoming segments but more load on the system.
> 
> END
> 
> >What am I missing?
> 
> All you are missing is the fact FreeBSD cannot handle
> two NICs the same subnet. OpenBSD does, NetBSD does and Linux does.

That sounds misleading. FreeBSD handles two or more NICS on one subnet.
You just can't configure them with same netmask or have them behave
identically.
Only one can be default gateway.

> Regards
> 
> Bob D
> 
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