Community discussions

MikroTik App
 
User avatar
Kentzo
Long time Member
Long time Member
Topic Author
Posts: 512
Joined: Mon Jan 27, 2014 3:35 pm
Location: California

Wireless bridges and virtual network bridges

Thu May 25, 2023 10:52 am

My understanding is that a wireless bridge allows to transparently join broadcast domains such that /interface/bridge/host on each node of the wireless connection will include wired hosts of the remaining nodes. With this arrangement it's clear how an L3 segment may be created to enclose devices of all nodes.

When I create a virtual network bridge on my Windows laptop, e.g. between a wireless connection and a VMware virtual ethernet adapter, these bridged devices somehow join my L3 segment (/ip/arp, /ip/dhcp-server/leases). However, my Mikrotik AP does not recognize laptop's wireless connection as bridged (per /interface/wireless/registration-table) nor these bridged devices appear in /interface/bridge/host.

How does this work, i.e. single L3 segment exists over multiple L2 segments?
 
User avatar
mkx
Forum Guru
Forum Guru
Posts: 11381
Joined: Thu Mar 03, 2016 10:23 pm

Re: Wireless bridges and virtual network bridges

Thu May 25, 2023 11:15 am

Wireless standard 802.11 doesn't specify 4-address mode, which is required for true bridge (as in: L2 transparent) between "wired islands". Different WiFi vendors came up with proprietary extensions[*] and those extensions are not compatible. Which means that bridge is only possible between wireless devices, made by same vendor. When tehre's a combination of different vendor equipment, some vendors implemented some work-arounds, but then the other device doesn't see the link as bridge and things might not work 100% reliably (broadcasts might get mis-delivered ... DHCP handshake works (partly) over broadcasts so DHCP assignments might fail).

You can read more about the issue in this article: https://wiki.mikrotik.com/wiki/Manual:W ... tion_Modes

[*]Mikrotik did as well, but it's not supported by wifiwave2 driver (yet?).
 
wiseroute
Member
Member
Posts: 352
Joined: Sun Feb 05, 2023 11:06 am

Re: Wireless bridges and virtual network bridges

Thu May 25, 2023 11:57 am

hello kentzo,

[*]
However, my Mikrotik AP does not recognize laptop's wireless connection as bridged (per /interface/wireless/registration-table) nor these bridged devices appear in /interface/bridge/host.
[*]

it is because the only device which has real physical connection to the ap was only laptop's wireless nic.

from dhcp server pov - as long as the broadcast medium are there then it should listen to any requests, - whichever wired/wireless/bridge/virtual Ethernet mac came it should give ip (of course, limited by policy). ie. your laptop's wired/wireless nic, your virtual Ethernet vm, which bridged to bridge mini port --> they all could reach out to dhcp (including the bridge itself) as long as no barrier there.

but on the ap - it only knows your wireless nic connected to it.

hope this helps.
 
User avatar
Kentzo
Long time Member
Long time Member
Topic Author
Posts: 512
Joined: Mon Jan 27, 2014 3:35 pm
Location: California

Re: Wireless bridges and virtual network bridges

Thu May 25, 2023 9:21 pm

@mkx, I see now that bridging is proprietary and it's unlikely to expect end-user client device to establish a wireless connection in this mode with Mikrotik AP. Do I understand correctly that a virtual RouterOS running on my laptop with NIC connected to a virtual ethernet bridged with laptop's wireless cannot participate in (R/M)STP alongside the physical Mikrotik AP the laptop is connected to, because there is no L2 transparency (AP thinks that the corresponding bridge port is "edge").

@wiseroute, Do you mean protocols based on L3 broadcast medium going to work while those based on L2 won't? Is it achieved because Windows, in case of bridged wireless and "wired", acts as L3 relay?

I'd appreciate an example of purely physical network with similar topology, i.e. one L3 broadcast domain over multiple L2 broadcast domains.
 
User avatar
Kentzo
Long time Member
Long time Member
Topic Author
Posts: 512
Joined: Mon Jan 27, 2014 3:35 pm
Location: California

Re: Wireless bridges and virtual network bridges

Fri May 26, 2023 1:33 am

With Wireshark I see that:

- By tapping on virtual Mikrotik's ethernet that it sends BPDUs (it considers itself the root, incorrectly due to higher priority)
- By tapping on laptop's wireless that it forwards these BPDUs after changing 802.3 Source to its own
- By tapping on physical Mikrotik AP's wireless that it sends BPDUs (it considers itself the root, correctly due to lower priority)

None of the nodes see BPDU of the opposite: Neither laptop nor virtual Mikrotik sees BPDU of physical Mikrotik and vice versa. It's unclear to me why that happens and whether lack of wireless bridge is involved.
 
User avatar
Kentzo
Long time Member
Long time Member
Topic Author
Posts: 512
Joined: Mon Jan 27, 2014 3:35 pm
Location: California

Re: Wireless bridges and virtual network bridges

Fri May 26, 2023 3:11 am

Perhaps Windows just consumes BPDU's from both sides... and does not relay it. Wonder how I could diagnose this.
 
wiseroute
Member
Member
Posts: 352
Joined: Sun Feb 05, 2023 11:06 am

Re: Wireless bridges and virtual network bridges

Fri May 26, 2023 3:27 am

[*]
None of the nodes see BPDU of the opposite
[*]

have you set your Wireshark interface - or the whole connected interface in your lab to be in promiscuous mode?
 
User avatar
Kentzo
Long time Member
Long time Member
Topic Author
Posts: 512
Joined: Mon Jan 27, 2014 3:35 pm
Location: California

Re: Wireless bridges and virtual network bridges

Fri May 26, 2023 8:07 am

have you set your Wireshark interface - or the whole connected interface in your lab to be in promiscuous mode?
Tried either way when tapping on the wireless interface of the laptop.
 
User avatar
mkx
Forum Guru
Forum Guru
Posts: 11381
Joined: Thu Mar 03, 2016 10:23 pm

Re: Wireless bridges and virtual network bridges

Fri May 26, 2023 9:08 am

Regarding "unusual" traffic over wireless link: I'm guessing that it boils down to wireless driver (on both sides). Experience goes that (legacy) Mikrotik wireless driver doesn't mess with packets. However some windows drivers (both wired and wireless) are known to "play smart ass". Since WiFi, according to standards, is not intended as interconnect link between two parts of network, this automatically means that wireless link is intended to be "edge port" of anything. So I wouldn't be surprised too much if windows wireless driver would simply drop BPDUs (and anything similar).

Personally I don't see much point in pursuing this matter ... unless you know that there might be a loop, e.g. because the same physical machine is connected to the rest of network with another link, such as UTP.
 
User avatar
Kentzo
Long time Member
Long time Member
Topic Author
Posts: 512
Joined: Mon Jan 27, 2014 3:35 pm
Location: California

Re: Wireless bridges and virtual network bridges

Fri May 26, 2023 9:17 pm

Initially that was for a home lab. Since my network simulator (GNS3) doesn't handle Wireless I wanted to introduce physical equipment to my setup, i.e. arbitrary virtual topologies on each side of physical wireless network. Looks like I should run some linux distro for that, for better control.

However, It's not entirely clear to me in which cases I must have client in station-bridge, assuming the client is doing translation.

Who is online

Users browsing this forum: phascogale and 55 guests