REPLY: 2:5020/545 61da7f32
MSGID: 2:5005/49 61da88e0
CHRS: CP866 2
TZUTC: 0700
TID: hpt/fbsd 1.9.0-cur 2019-12-05
Dear Alexey,

09 Jan 22 09:21, you wrote to me:

 TK>>>>> I have a wireguard server running in my VPS (Ubuntu 20.04.3
 TK>>>>> LTS). It is using a /112 of /64 for it's clients.
 VS>>>> Do you mean to say you can have a /64 network on your VPS' main
 VS>>>> interface and at the same time a /112 from the *same* *network*
 VS>>>> on a wg0 interface? Is this even permitted by the OS?
 AV>>> Yes - at least properly configured Linux allows this.
 VS>> What do you mean by "properly configured"? You mean the
 VS>> out-of-the-box configuration still does not allow this?

 AV> Obviously.

What do you need to configure to enable this behaviour on Linux?

 VS>> A Cisco router would not allow the same L2 network on two
 VS>> different L3 interfaces IMHO, even if one of the prefixes is more
 VS>> specific.

 AV> That's a limitation of BSD-style IP stack.

Interestingly enough, FreeBSD 12.3 has just let me do exactly that (sorry, an
IPv4 example), without any additional configuration. The world is full of
wonders:

root@vas:~ # apply ifconfig lo{2,3}
lo2: flags=8049 metric 0 mtu 16384
        options=680003
        inet 192.168.13.1/24
        groups: lo
        nd6 options=29
lo3: flags=8049 metric 0 mtu 16384
        options=680003
        inet 192.168.13.129/25
        groups: lo
        nd6 options=29
root@vas:~ #
root@vas:~ # apply 'route get ' 192.168.13.2 192.168.13.200
   route to: 192.168.13.2
destination: 192.168.13.0
       mask: 255.255.255.0
        fib: 0
  interface: lo2
      flags: 
 recvpipe  sendpipe  ssthresh  rtt,msec    mtu        weight    expire
       0         0         0         0     16384         1         0

   route to: 192.168.13.200
destination: 192.168.13.128
       mask: 255.255.255.128
        fib: 0
  interface: lo3
      flags: 
 recvpipe  sendpipe  ssthresh  rtt,msec    mtu        weight    expire
       0         0         0         0     16384         1         0
root@vas:~ #



Victor Sudakov, VAS4-RIPE, VAS47-RIPN
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