multiple interfaces on same subnet?
malcolm.kay at internode.on.net
Tue Aug 1 23:37:35 UTC 2006
On Tue, 1 Aug 2006 05:10 am, Joseph Gleason wrote:
> Is it possible to reach two hosts via two interfaces that are
> both on the same subnet?
> em0: 172.20.0.1/16
> em1: 172.20.0.2/16
> And I want to reach 172.20.0.3 via em0 and 172.20.0.4 via em1.
> From 'netstat -nr' I see a line like this:
> 172.20/14 link#1 UC 0 0
> This seems to say that anything on 172.20/14 should be reached
> on em0. Is it possible to add a rule that says that 172.20.0.4
> should be reachable on em1?
I have no personal experience of doing this, but it seems to me
you should be able to achieve your objective by using a specific
netmask with ifconfig rather than the CIDR / notation:
172.20.0.1/16 -> 172.20.0.1 netmask 255.255.0.1
172.20.0.2/16 -> 172.20.0.1 netmask 255.255.0.1
Then as I understand it odd numbered addresses should be reached
via 172.20.0.1 and even numbered addresses via 172.20.0.2
> I only care about the path of outbound packets. I don't care
> which interface inbound traffic comes on.
> I am well aware that this is a fairly strange thing to do.
> My objective is to have a FreeBSD box balance outbound traffic
> between two NICs, while being able to select from among many
> routers that could be the default gateway and having the two
> NICs connect to different switches for fault tolerance. (I
> would do the fault tolerance via a watchdog script of some
> If it weren't for the many routers aspect, it would be
> reasonable to create separate subnets. I need to be able to
> select from a group of around 10 possible default gateways and
> some of those routers I do not control so adding a subnet
> would be trouble.
I would expect that subnets in the routers would not be an issue
so long as they encompass those set in ifconfig.
More information about the freebsd-questions