bin/55649: /sbin/route add doesn't accept with -interface parameter

[dogan%tesmer.org.tr@localhost]

>Number:         55649
>Category:       bin
>Synopsis:       /sbin/route add doesn't accept with -interface parameter
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    bin-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Sep 09 19:40:00 +0000 2020
>Originator:     Mustafa Dogan
>Release:        NetBSD 9.0_STABLE amd64
>Organization:
TESMER Temel Egitim ve Staj Merkezi
>Environment:
NetBSD localhost 9.0_STABLE NetBSD 9.0_STABLE (GENERIC) #0: Fri Sep  4 09:09:14 +03 2020  root@localhost:/root/OBJ/sys/arch/amd64/compile/GENERIC amd64

>Description:
When I was setting a route for openfortivpn ppp interface, I encountered
/sbin/route -n add -net 172.16.16.0 -netmask 255.255.254.0 -interface ppp0
route: ppp0: bad value
lines on the console. Then I tried route (8) command with several network adapters (re0, iwm0, etc) several times, but every time I got the same response: route: netadapter: bad value.  

However, in the route(8) man page says that:
"If the destination is directly reachable via an interface requiring no     intermediary system to act as a gateway, the -interface modifier should be specified; the gateway given is the address of this host on the common network, indicating the interface to be used for transmission."

I used route (8) like this:
route -n add -net 172.16.16.0 -netmask 255.255.254.0 10.0.0.1
(10.0.0.1 is IP address of ppp0 interface) and it worked as expected.
Is there a problem, or am I missing something?
>How-To-Repeat:
Use route(8) with -interface parameter.
/sbin/route -n add -net x.y.z.0 -netmask 255.255.255.0 -interface $intf
x.y.z.0 is destination network address and $intf is network adapter (re0, wm1, bge2, etc).
>Fix: