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MichaelNa
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Joined: Sun Dec 01, 2019 10:22 am

Alternative hardware weirdness on layer 2

Sun Jun 13, 2021 8:37 pm

Hi.

I installed RouterOS on a 10 year old Mushroom Truffle Lite Bonding Appliance because RouterOS is awesome and you know.... you can. :-)

Anyways, result awesome. 6 Gbit ports, 4 Core Atom D510 CPU@1.6 Ghz, 1 GB RAM, CFlash for boot, space for HDD+ more RAM, etc and going like a Boeing.
All good until I noticed the weirdness:

I can MAC-connect (Winbox or Mac-telnet) to the MAC of a port that is not physically connected. I do mean that exactly as written. Winbox to port 1 on it's mac xx:xx:xx:xx:xx:xx and all good. Switch the only cable on the device over to port 2; winbox to its mac yy:yy:yy:yy:yy:yy and also all good, but i can STILL connect to xx:xx:xx:xx:xx:xx as well! In fact I can do this to the MAC's of all 6 ports from any random port.

Worse; the discovery (LLDP) shows ONLY the connected port, but still allows MAC connect to any of the other five existing ports (which are in disconnect state!)

I actually whipped out a Hex to confirm I was still sane this was not standard behavior and I just hadn't noticed, which of course it wasn't, but how does one explain being able to access 5 other port's mac without any activity or connectivity from that port?

To be clear: with a completely empty config. Not even the default 192.168.88.1/24 setup.

So must be a hardware switch, right? Nope: connecting two ports does not result in a bridge or a loop. Running DHCP client on each port gets a different address for each port and expires correctly when you disconnect only that port. DHCP server confirms separate MAC's from each port.

To ultimately confirm there is no hardware switching (switch menu not listed in Winbox), I created a bridge over ether2 and ether3 whilst ether1 and ether2 are both connected to my own network. I connected aforementioned Hex to ether3. Ethernet2+3 pass network traffic correctly to the Hex. It correctly blocks when you either physically disconnect ether2 (IE not allowing from Ethernet1) or by disabling the ethernet2 bridge port while all hardware remains connected. Yet you can at any time mac connect to the Mushroom device on the MAC of the port you are NOT connected to.

To complete the magic; I can MAC connect and even remain connected to ether2's mac whilst disabling the ether2 interface after /interface ethernet disable ether2......

I am quite baffled. It is clearly not Mikrotik hardware so please understand this is not at all a support issue strictly me playing around on a Sunday afternoon, but I am highly intrigued what is causing this very weird behavior?

Any theories anyone?

Michael
Somewhere deep in Africa.

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