ARP mikrotik logic?

RouterOS General
1

Hello all. People need help in explaining the logic of mikrotik.
There mikrotik with this configuration:

# oct/22/2015 23:25:40 by RouterOS 6.32.2
# software id = 8G95-FVWF
#
/interface ethernet
set [ find default-name=ether1 ] name=ether1-master
set [ find default-name=ether2 ] master-port=ether1-master name=ether2-slave
set [ find default-name=ether3 ] master-port=ether1-master name=ether3-slave
set [ find default-name=ether4 ] master-port=ether1-master name=ether4-slave
set [ find default-name=ether5 ] master-port=ether1-master name=ether5-slave
/ip address
add address=192.168.0.254/20 interface=ether1-master network=192.168.0.0
/system clock
set time-zone-name=Europe/Moscow

And there’s a computer with:
IP: 192.168.1.1
Mask: 255.255.255.0
Gateway: 192.168.0.254

Why mikrotik computer sees clear. IP computer is in a range of masks mikrotik, but for some reason the computer sees mikrotik, why it works given that Gateway computers are not in its subnet?

The question is essentially to work with ARP mikrotik. If it’s okay if you do not know whether or not to change this logic routeros 7? After all, in fact it is wrong.

2

You see device in Neighbors even if it has no IP address. You can not connect to router by using IP address, but you can create MAC connection.

3

Yes, I understand. But here it is a matter of a little bit different. Why does my computer on the same network sees the device to another without routing and proxy arp?

Like this
A computer 192.168.1.1/24, the gateway is 192.168.0.1
The computer is 192.168.2.1/24, the gateway is 192.168.0.1
mikrotik 192.168.0.1/20

And these computers will see each other.

But if I do this:
A computer 192.168.1.1/24, the gateway is 192.168.0.1
The computer is 192.168.2.1/24, the gateway is 192.168.0.1
mikrotik 192.168.0.1/24

Communication lost.

I understand that the mask 20 allows mikrotik see both networks. But I do not understand that enables computers to see mikrotik. On Layer 2 I understand, at no Layer 3.

The same scheme on other vendors will not operate.

4

If by “seeing” you mean appearing in windows network, this happens because the windows network browsing protocol uses broadcasts (and/or link local IPv6 if enabled) to discover computers and workgroups.
As long as they share the same switch (like in your configuration), this is possible.
If “seeing” means connecting, communication being peer to peer, it depends on the computers firewall settings and the fact that the switch properly responds and forwards ARP requests. These requests will be properly answered if mask is /20 and also mikrotik will accept any unicast link belonging to /20 as a valid request (since all subnets belong to that /20 from the MT point of view, and the replies will go back the way they came in as unicasts, which don’t care about that netmask).

5

I have seen instances where if a host doesn’t get an ARP response for its gateway, it will just “broadcast” traffic for hosts it is trying to reach that are outside its subnet.

The other thing to bear in mind is that the packet on the wire doesn’t contain the netmask of the sending host, so there is no way the Mikrotik will know that you have configured your clients with the wrong netmask.