Hi everyone,

after finding a few threads that have a similar topic, but none with the configuration I have in mind, I though I'll ask the proven source of truth.

I'm looking to implement the following scenario:
- A vehicle provides Internet access via LTE while on tour and shares the access to the devices on board the vehicle.
- Once the vehicle is back in the garage/station, the internet access is not via LTE but via the provided WiFi (This will be done by a failover-routing like "default-GW is local LAN-Router, if not available, switch routing to LTE")
- We are talking about 3 to 7 vehicles, each with 1-4 devices that access the onboard-wifi

My approach:
- Take a LTAPmini
- configure LTE Access
- configure an AP for the onboard wifi
- configure a wifi in station mode to connect to the wifi provided when back in the garage/station.

Issues/Questions:
================
- The LTAPmini only has one 2GHZ-Radio with dualchain, so configure wireless-interface an a virtual wireless interface. Based on other threads, the virtual wifi-interface usually vanishes when the master-wifi is gone (e.g. Travelrouterconfig with MAP2n). So I would need to configure the msater-wifi as the Accesspoint and the station-mode on the virtual wifi-interface. At least that worked so far. The only caveat is that I have to set the frequency of the master-wifi (AP-Mode) manually to the frequency of the AP used in the garage. Otherwise the virtual wifi-interface (StationMode) won't find the AP to connect, when returning home, as the virtual interface will always use the frequency of the master-interface. Now, did I get that right and second, is there a more elegant way?

- Building bridges....do I need a bridge? As all traffic from the AP/master-interface is either routed to the LTE-Interface or the virtual-wireless-interface I believe I don't need a bridge from that perspective. So I would only configure a bridge to access the LTAPmini itself, right? Which interfaces should be added to the bridge, ether1, main-wifi, virtual-wifi, LTE? I would assume the first three mentioned, as it allows me to access the LTAPmini from an ethernetcable, via the local onboard wifi and remote through the garage/station wifi provided.

- Providing to Wifis/SSIDs on the same frequency will impact performance, at least in theory. Based on the values mentioned earlier, do you see an issue here. I need to add, that the traffic from the devices is going to be low on average, mainly receiving mails/messages and an update once in a while.

Appreciate your share of expertise,

cheers,
Plani

- There's no elegant way around the problem using single radio. To make sure LTAP mini connects to garage WiFi, master wireless interface has to be configured as client ... which in turn drops the slave interface (in-car AP) when master interface is not connected (it's scanning through all channels to find the AP to connect to). One could make a script that after master interface looses access to garage AP, it reconfigures wireless so that in-car AP is on master interface. The problem is going back to previous setup (master being client of garage AP) when car returns to garage. Perhaps one could perform a background scan every few minutes when in "in-car wifi only" mode and if garage SSID is detected, wireless could be reconfigured back to master/slave?

- if you don't intend to use wired interfaces, you don't need bridges. Device will route traffic between in-car slave interface and garage master interface when car is in garage ... or it will route traffice between in-car master interface and LTE interface. If, however, you'd be using wired interfaces as well, you'd have to bridge wired interfaces with in-car wireless interface (whichever it is at the moment) and route traffic from bridge towards whatever upstream at the moment. If you only need wired for managing LTAP, then you don't need bridge ... simply configure dedicated subnet (IP address, DHCP server, ...) directly to wired interface.

- when car is in garage, the impact of this device will be very considerable: packets will use air time on same frequency at least two times (device to LTAP, LTAP to garage AP ... similarly on the way back), but the effect is even bigger than halving the throughput because the chances of collisions will be much higher than when using single AP per channel.

All in all it would be much better if you used separate device for in-car AP, preferably a 5GHz one. This would make problem of detecting garage AP much easier and throughput problem would largely go away. But this solution comes with price of additional AP and a bit higher power consumption (comes into play if gear is powered also when car's engine is off).

I Agree,

The "easy" solution would be the Mikrotik wAP ac LTE kit.
ethernet-Interfaces and 5Ghz for the Clients
2.4 Ghz for the Garage-Wlan as WAN1
LTE as WAN2

Great, thanks for the fast reply.

Just two more questions:
a) @mkx: You said: "master wireless interface has to be configured as client". Why is that? My logic was, the master-wireless-interface running as AP will 'never fail' while in the meantime the virtual-wireless-interface can try to connect infinitely. What did I miss?

b) I just saw the Mikrotik wAP ac LTE kit and wonder if there is a reason to not install it in a vehicle, like robustness, powersupply etc. I mean, the only difference I can see is the missing GPS, which wouldn't be a mandatory requirement.

Cheers

a) @mkx: You said: "master wireless interface has to be configured as client". Why is that? My logic was, the master-wireless-interface running as AP will 'never fail' while in the meantime the virtual-wireless-interface can try to connect infinitely. What did I miss?

It sadly doenst work like that !
The Master Interface ist always going to be in "Station-Mode" / Wifi-Client
Wifi-Band, Frequency and Co. will be define by your Wifi-Network

The Virtual-Interface as AP-Bridge will piggyback on the Station-Mode

Do you realy want to use car Internet while you are in the garage/station?

IMHO the best solution is to configure ltAP mini with SSID identical to home SSID.
When your car is "at home" you just switch off Mikrotik and devices reconnect to home AP with same SSID.
When you travel and you are outside home WLAN all you devices just connect to car WiFi.

@ConnyMercier: But it did work. Here is the export of the config I User today: I mean Theresa is no proper routing and Nottingham configured, but the functionality is given.

@BartoszP: Good point you have there. The only caveat ist that I can't do remote Management since I can't see the LTAP when it is not connected to the local wifi

Guten Abend aus BW,

I have a LTAP lying around i tried it out!
I got it to Work too,
but a soon as the Frequency, ChannelWidth and Co. doesnt match your "Garage-Wifi" you will not get a connection.


Sooo, if you go that route, no Auto-Frequency and Co. =)

Use https://mikrotik.com/product/RBmAPL-2nD as client for home WiFi or any other WLAN eg. HotSpots or campings WiFi and connect it via Ethernet to ltAP.

a) @mkx: You said: "master wireless interface has to be configured as client". Why is that? My logic was, the master-wireless-interface running as AP will 'never fail' while in the meantime the virtual-wireless-interface can try to connect infinitely. What did I miss?

It sadly doenst work like that !

It can work like this just the way @plani already checked. The problem is that client has to follow whatever AP chooses for its radio settings. If you set radio settings on master wireless interface (n.b. slave doesn't have radio settings) to match those of AP, then client is able to connect. However, if AP is set to change parameters if needed (e.g. select different channel and/or channel layout due to changes in interference), then client won't be able to follow. Or if there are multiple "garage" APs with same SSID but different radio settings and it is desirable to have car gear connect to any of them. That's why I said that master interface has to be configured as client.

Powering wAP ac LTE kit is almost as robust as LTAP mini's ... minimum supply voltage is 10V (compared to 8V of LTAP) which shouldn't be a problem as long as car battery is in good condition (voltage drops in car power system during engine crank-up). But then it depends on how you intend to wire the wifi gear. I strongly discourage wiring without a power switch, even though rated power consumption of LTAP mini is only 9W, that's still around 0.75A ... can drain typical small-engine car battery (those are rated as low as 35Ah) in less than 48 hours.
If you planned to power the gear "automatically" with contact key, this would prevent from draining the battery, but would still expose gear to short-term under voltage condition. If you install a powering solution which requires manual switch-on together with automatic switch off (with contact key) you could avoid undervoltage condition by starting the gear while engine is already running.
Another possibility would be to keep contact key powering method, but to install voltage boosting circuit which would raise voltage to say 24V (both wAP ac and LTAP mini can be powered with 24V) ... those circuits can typically take supply voltages as low as 5V ... but come with their own power consumption which makes need for on-demand powering even more urgent.

Thank you all for the good feedback. The quick proof of concept showed that although it is doable, it should not be implemented, especially if thought of as a professional, reliable solution. To summarize:
- Sharing the Wifi for internal AP and station/client mode will reduce performance noticeable
- The definition of the Sation-WiFI settings to predetermined Frequencies etc. goes with a high risk to break as soon as the garage-AP changes frequencies etc. for whatever reason out of your control

Solution: The solution will be a wAP ac LTE kit, giving two WiFi-Radios, only lacking the GPS part, which again wasn't a requirement. Otherwise one would need two devices as @BartoszP proposed or an AP in the garage under your control, which both mean additional costs and management efforts, so the wAP ac LTE kit is prefered.

@mkx: Many thanks for the details on the cabling/powering. What I didn't mention is that this solution is being thought of to provide Internet-access for devices on a fire-engine/truck. They are generally charged while in the garage and further charge different devices like handheld radios and flash-light onboard. So we are not talking about a 35ah-Battery, and based on your writing I see no further issue in installing one.

Many thanks to you all and have a nice Sunday.

Cheers,
Jan

@ConnyMercier: Guten morgen aus HE

P.S: I'll take the LTAPmini now as an AP for my garden WiFI coverage and as LTE-Failover for my DSL.