CLI/GUI doesn't prevent multiple interfaces from being configured with the same IP address

[gcooper]

Procedure:

• Log in to CLI/GUI.
• Configure interface A with IP address 192.168.20.1/24.
• Configure interface B with IP address 192.168.20.1/24.

Expected result:

• Interface A should be configured with 192.168.20.1/24; interface B on the other hand should be rejected.

Actual result:

• Both interfaces are configured with 192.168.20.1/24.

[jgreco]

If you're going to prevent PEBCAK errors of that class, then it should be noted that you also need to prevent two IP addresses on the same *network* (such as 192.168.20.1/24 and 192.168.20.2/24) or you're just preventing a trivial error while allowing a much more likely error. Blocking two addresses on the same network will also block two identical IP addresses.

[gcooper]

Replying to jgreco:

If you're going to prevent PEBCAK errors of that class, then it should be noted that you also need to prevent two IP addresses on the same *network* (such as 192.168.20.1/24 and 192.168.20.2/24) or you're just preventing a trivial error while allowing a much more likely error. Blocking two addresses on the same network will also block two identical IP addresses.

That argument doesn't make sense 100% because you can have multiple interfaces on the same network/netmask.. you just can't have multiple physical interfaces bound to the same address. Granted, you can pull tricks where 10.0.0.0/16 and 10.0.2.0/24 both deal with the same address space, but that's not the issue that needs to be resolved here.

FreeBSD doesn't prevent me from doing something like:

ifconfig_em0="inet 10.0.0.1"
ifconfig_em1="inet 10.0.0.1"

and that's a problem because it confuses the network subsystem in the kernel -- you should be creating a lagg if you want to do that.

[jgreco]

FreeBSD now allows two interfaces on the same network with different IP addresses? If so, that's news to me, but I suppose it's possible.

[zippybr]

In [8821/freenas]:

first pass to fix #926

[william]

Should be fixed in r8821, r8823 and r8824