[HN Gopher] Simultaneous AP and Client Mode Wi-Fi on Raspberry P...
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Simultaneous AP and Client Mode Wi-Fi on Raspberry Pi Zero W
Author : lukicdarkoo
Score : 211 points
Date : 2020-08-23 10:36 UTC (12 hours ago)
(HTM) web link (github.com)
(TXT) w3m dump (github.com)
| reactchain wrote:
| Has anyone noticed a shortage of Pi Zeros recently? It seems
| everywhere has run out of stock.
| capableweb wrote:
| Recently? I've seen a shortage (in EU shops (Pi Zero W
| specifically)) since it was launched and seems it's not getting
| better either.
| kingosticks wrote:
| Comes and goes. As it happens they are back in at
| https://shop.pimoroni.com/products/raspberry-pi-zero-w
| (limited to 1 per order).
| LeoPanthera wrote:
| I think this is intentional. The Pi Zero is mostly a marketing
| device. It's advertised at $5 but unless you happen to have a
| physical store selling them near you, it's not really $5
| because the shipping is never free and you can only ever by
| one. So it's more like $15.
|
| Still not a crazy price, of course, I just dislike the
| misleading advertising.
| mleo wrote:
| More time to tinker at home? Over the course of a couple weeks,
| I purchased four a two months back. A project I worked on
| inspired at least another person in my office to buy one.
| wil421 wrote:
| My local microcenter has been jammed packed since the
| pandemic started. I also purchased 2 a few months back and a
| bunch of accessories.
| rootsudo wrote:
| Always, it's been "limit:1" but you can buy the different kits,
| even from the same vendor but not for $5.
| basilfx wrote:
| I've been using a similar solution, but I had quite some problems
| using AP and client mode at the same time. The WiFi chip inside
| the RPi Zero W (BCM43430) only supports AP and client mode on the
| same channel. If you setup an AP first, then connect to a client
| network, hostapd will update the channel of the AP, but clients
| will notice a disconnect. There are also issues with the firmware
| blob (see https://github.com/raspberrypi/firmware/issues/1403) in
| AP mode that haven't been solved yet.
| watchdogtimer wrote:
| What I did on a similar project using a different board was
| scan all the APs in the area first, get the band of the AP with
| the strongest signal, then bring up the device AP using that
| band. I figured the AP with the strongest signal is the closest
| AP and the one you most likely want to connect to.
| cptskippy wrote:
| This is perfect for hotels whose TV sucks and their wifi has
| those captive portals so you can't use a Chromecast, Firestick,
| or Roku.
|
| It just needs a captive portal of its own when the client side is
| disconnected.
| non-entity wrote:
| Just curious, but I was trying to help someone with a Raspberry
| Pi Zero W wifi issue the other day and had trouble finding sny
| info about the wireless chipset used. I couldn't find it listen
| anywhere on the site, or several tech review sites, only
| extremely useless information on the 802.11 versions support. If
| it recall correctly, it didn't even show up in the schematica.
| Luckily wikipedia had the name of the chipset used, but I don't
| get it. Why does their official documentation seem to be so
| secretive?
| dc_count wrote:
| It's not secretive, it's just that most people are not very
| interested in the exact type of Wi-Fi chipset used.
|
| You can see the chipset name (BCM43430) on dmesg:
| $ dmesg | grep brcmfmac [ 26.488164] brcmfmac: F1
| signature read @0x18000000=0x1541a9a6 [ 26.512759]
| brcmfmac: brcmf_fw_alloc_request: using brcm/brcmfmac43430-sdio
| for chip BCM43430/1 [ 26.513315] usbcore: registered
| new interface driver brcmfmac [ 26.539406] brcmfmac
| mmc1:0001:1: Direct firmware load for
| brcm/brcmfmac43430-sdio.raspberrypi,model-zero-w.txt
| messe wrote:
| Whatever happened to ad-hoc mode?
| cordite wrote:
| I haven't considered this since the days of Nintendo DS picto
| chat.
| capableweb wrote:
| Not sure exactly what you're referring to, did the author
| explain in the past they rather want ad-hoc network setup or
| something?
|
| Otherwise, ad-hoc is different from AP+Client, as ad-hoc is
| only between two devices (at least from what I gather) while
| AP+Client would allow a distributed network where clients are
| interconnected.
| jiggunjer wrote:
| I thought ad-hoc is N devices, optionally decentralized. This
| could emulate that.
| ausjke wrote:
| ad-hoc in general runs a different path inside kernel module,
| which is normally not supported as well as AP/client mode, so,
| while many chips can do ah-hoc in theory, in software side it
| is a difference story
| mschuster91 wrote:
| It's extremely rare that one gets to a working ad-hoc setup...
| it's a chicken-egg problem. Drivers, firmware, software and UI
| support are bad, so no one uses it, so development is an
| afterthought, rinse and repeat.
| punnerud wrote:
| How to get faster internet at a hotel: Have 4-5 of these
| connected and talking with the hotels WiFi, and one who share
| Internet with you. All the traffic goes to a server you have at
| home that "join+proxy" the traffic. Based on the idea that every
| user have a limited bandwidth, combining multiple will give you
| higher speed.
| woleium wrote:
| or just route over icmp or dns
| ngcc_hk wrote:
| Why is that not easy and widely used as nearly all devices we
| used like camera (dslr to car camera) and remote controller all
| resolved to stop WiFi and switch to another mode etc to connect.
| caust1c wrote:
| Partially because of chip capabilities, and partially because
| understanding networking is hard.
|
| I don't think most chips can do this fwiw, but it's definitely
| cheap enough now that cameras and IoT devices will probably
| start doing it everywhere.
| 7ewis wrote:
| Would this be good for something like connecting the Pi to a VPN
| for say Canada, then broadcasting an SSID for it.
|
| Then connecting a Fire TV Stick or Chromecast to this AP, and
| tricking it into letting you stream Canadian Netflix or DAZN etc.
| gzu wrote:
| I was interested in setting up something similar (as a novelty)
| to cheaply bypass an untrusted network.
|
| Untrusted Wifi > RasPi Client > OpenVPN > AP
|
| How would you go about routing the VPN device between client
| and AP?
| derefr wrote:
| Maybe it was just an arbitrary example, but really, there's no
| reason to want Canadian Netflix. We only get about half the
| stuff the US does.
|
| Also, we have the same "content can't be offered here by
| Netflix because the local IP license has been bought out by a
| different owner" problem that the US and many other places
| does; but in Canada's case, most of those local IP owners are
| conservative dinosaur media companies, who either haven't
| managed, or haven't bothered, to set up their own alternative
| streaming services yet. They just... hold the licenses, doing
| nothing with them. Hoarding them, like a dragon. So there are
| many shows you just can't stream in Canada at all, no matter
| who you're willing to pay.
| yeswecatan wrote:
| Sounds like it would work. I may give that a try. Now to find a
| VPN for Canada...
|
| edit: Now that I think about it, what's the difference between
| using the Pi as an AP and using it as a DNS server?
| Raed667 wrote:
| A bit off topic:
|
| I'm looking for a project that starts with an AP. Once someone
| connected to it; it opens a web page to configure the client
| (choose which WIFI from a list, and type the password).
|
| It connects to the chosen WIFI and shuts down the AP.
|
| Anyone here did something similar to that?
| ncrmro wrote:
| ESP-32 + captive portal?
|
| https://github.com/tonyp7/esp32-wifi-manager
| flak48 wrote:
| Yep. I didn't do it with a RasPi but with a Chinese chip I
| found off AliExpress
|
| Managed to strip down OpenWRT so it would fit in the meager
| 16MB RAM/8MB flash. In the init script (a bash script) just
| checked if a wifi network was configured previously (creds
| stored in a file).
|
| If configured, try to connect to the network for 10 seconds. If
| it couldn't connect, then switch to AP mode and start a
| lightHTTPd server listening on 192.168.0.1:80.
|
| The only files it served was a simple index.html with some JS
| that called a bash script via CGI that used a openwrt bash
| library to scan and list the available wifi networks.
|
| Then a HTML form to choose an SSID and enter the password, upon
| submit call another bash file to connect to the network (switch
| to client mode) with a timeout. If it fails, the bash would
| switch back to AP mode.
|
| Polling in JS to check if the connection was successful (by
| checking if AP mode becomes active again)
| voltagex_ wrote:
| WifiManager for the ESP8266/ESP32 will do that.
| jiggunjer wrote:
| This is basically what a chromecast does?
| Raed667 wrote:
| Exactly, I want to replicate that behavior in Raspberry Pi.
| savrajsingh wrote:
| Starting point: https://github.com/balena-io/wifi-connect
| numpad0 wrote:
| I've seen Raspberry Pi images from Ubiquity Robotics(not
| Ubiquiti Networks) having similar daemon called "pifi" for
| command line operation, but this one looks nicer
| nebalee wrote:
| https://github.com/davesteele/comitup does this. No idea how
| well it works, I have not tried it yet.
| kingosticks wrote:
| https://github.com/billz/raspap-webgui
| sdfhbdf wrote:
| I've looked at the links posted here and the repo but I fail to
| find what is the use case for this?
| jonpurdy wrote:
| I use a Pi Zero W + extra USB wifi to share modern wifi with my
| legacy PowerBook 2400c + 802.11b PCMCIA card.
|
| This setup could let me do it without the USB wifi hanging off
| the USB OTG adaptor.
|
| * This is not secure but it's fine for my vintage computing
| hobby
| lostapathy wrote:
| I use a pi this way so I can join my pi to hotel wifi (or
| similar) then join my iPad to the pi's network - which lets me
| ssh into the pi to access software there while both devices
| have internet access.
| rootsudo wrote:
| I do the same with a pocket wifi router, and clone the mac
| address. So, nifty and interesting case for the pi too!
| Thanks!
| gumby wrote:
| Ever stay at a hotel that charges for wifi access on a per
| device basis?
| BossingAround wrote:
| I've never stayed at a hotel that'd charge extra for wifi.
| Airports and planes thoug, sure.
| dboreham wrote:
| No, but it's not uncommon to find hotel internet that has a
| fairly low device count limit. The place I use WiFi repeaters
| is on airplanes, to avoid the hassle of re-authenticating
| every time I switch between phone and tablet and laptop.
| post_break wrote:
| A perfect MITM device that is tiny and can be hidden somewhere
| is my first use case. Micro pineapple.
| opencl wrote:
| It could be used as a range extender, though not a very good
| one.
|
| Probably a better use case would be connecting older devices
| like the Nintendo DS that don't support WPA2 to your network
| without forcing all of your other devices onto WEP.
| sleavey wrote:
| Why not a very good one? In terms of range (with the PCB
| antenna)? Or does the Pi firmware not support some modern
| 802.11 standards or what?
| flaviu2 wrote:
| I'd guess the hardware is the problem. Most antennas I've
| seen on access points are larger than the entire Pi Zero W.
| While I'm no radio expert, I'd expect APs to use the
| smaller antennas if they were capable of being as good as
| bigger antennas.
| sleavey wrote:
| Ah, that reminds me of an article someone here linked to
| a few years ago: [1]. That claims the efficiency is -3.5
| dB compared to a typical -1.25 dB dipole in dedicated
| wireless equipment. Not bad; the difference is only a
| factor of ~2 in power for x8 reduction in size.
|
| [1] https://www.embedded-computing.com/articles/a-lesson-
| in-wire...
| zamadatix wrote:
| Well 2 things really. Yeah the hardware is a bit garbage as
| it only goes up to 802.11n only on 2.4 GHz and it's also a
| 1x1 with a poor antenna. The big thing though is it
| requires you use the same channel which is disastrous for
| repeater performance.
|
| Ideally you'd have 802.11ac/ax with 2 separate PHYs each
| with 4x4 (even if the clients are 1x1 or 2x2 the additional
| beamforming helps) set to two separate channels.
|
| That's not to say it won't function well enough in a pinch
| but I wouldn't seek this out as a permanent answer if I
| were buying new.
| muppet_frog wrote:
| ...sounds like it costs _much_ more than the $10 pi0...
|
| I imagine the OP's use case of IoT did not require huge
| amounts of bandwidth.
| zamadatix wrote:
| "That's not to say it won't function well enough in a
| pinch but I wouldn't seek this out as a permanent answer
| if I were buying new."
|
| Like I said this functions fine, as is evident by it
| having been posted, but the question was why it wasn't a
| very good repeater not was it a functional use of an
| existing pi 0 laying around.
|
| It's also not the best you could do buying new if that is
| what you had to do as ~$16 will get you a 2x2 802.11n
| repeater that functions much better, has external
| antennas, and has an ethernet port too. Not $10 but it's
| also enclosed and doesn't need a power supply or uSD.
| ~$30 will get you decent AC repeaters you could use
| outside of a singular IoT project. Less for either if
| you're willing to go used. The ideal 4x4 ax double phy
| wireless repeater is indeed going to be more than a pi 0
| but it was an example of what makes a repeater good (to
| the question) not what should have been purchased for
| this project.
|
| Again nothing wrong with the solution used here, that's
| not where my comment was pointed.
| agarzenm wrote:
| The use case is in the title. You can use it as a wireless
| repeater. A more interesting use case would be ethernet over
| USB and a wireless AP with another interface for client
| monitoring via airmon.
| karmicthreat wrote:
| I use this for configuration on some equipment I sell. The unit
| has a local web server that lets you configure IP, ID
| information. It works as a captive portal. Then you just plug
| your ethernet cable in and its good to go. (I use a Pi 3 in the
| product).
| BossingAround wrote:
| I wonder what's the use case other than a poor wifi extender, or
| niche cases of sharing one connection between multiple devices
| where you pay per connection.
|
| Though I do wonder whether you can add a proper wifi antenna and
| make the RPI an 'ok' wifi extender. That might be a viable
| option, provided the performance is ok.
| EricE wrote:
| Or provide a gateway for wireless devices that don't support
| WPA2 Enterprise? Interesting....
| cmxch wrote:
| Initial configuration/management for the device in question.
| TaylorAlexander wrote:
| Would be good for a robot you can ssh in to at home and still
| connect when out in the field.
| noncoml wrote:
| VPN access point
| dcminter wrote:
| The pithier article (linked to from the above) is at
|
| https://blog.thewalr.us/2017/09/26/raspberry-pi-zero-w-simul...
| lukicdarkoo wrote:
| The script is heavily based on the article. Full credit to the
| article!
|
| For everybody interested in details, the article gives useful
| insights on configuration automated by the script.
| djsumdog wrote:
| I noticed the script was using the same MAC address for the ap0
| adapter. From that blog post...
|
| > A number of tutorials I found claimed that the address for
| the virtual AP must be different from the primary MAC address.
| I found there to be no difference in behavior, but you should
| be able to change the last byte, for example, to give your
| client and AP different MACs.
|
| huh ... You'd think this could cause interference, but I guess
| not if they have different SSIDs and passwords.
| brendawalsh wrote:
| Any idea why systemd was not able to be reliably used, and had to
| use cron?
|
| Is there a 'fix' for that ?
|
| edit: This was not meant to be offensive. I was simply hoping
| somebody could offer how it could be used with systemd and remove
| the reliance on cron.
| Nextgrid wrote:
| I think it's just a shortcut because of lack of experience with
| systemd (this is not intended to be offensive btw - if cron is
| already installed and you save time by just using what you
| know, why not?). I would be very surprised if cron could do
| something that can't be done with systemd timers.
| brendawalsh wrote:
| I saw the apt install cron, and wondered what the solution
| w/out cron entailed.
| lukicdarkoo wrote:
| I suspected that the network wasn't ready, so I configured
| the service start after network without much luck. I didn't
| go further than that.
| Nextgrid wrote:
| Systemd can be very powerful and you can even depend on
| individual devices being added/removed. I'm pretty sure you
| can even replace the udev rules with a systemd equivalent
| if you tried hard enough.
| lukicdarkoo wrote:
| No idea! I spent some time debugging it, but it just does't
| make sense it works with cron and not with systemd. Let me know
| if you have any idea where to look!
| nottorp wrote:
| Because systemd does many things badly instead of one thing
| well :)
| Dahoon wrote:
| So in short a poor range extender or a way to do MitM.
| op03 wrote:
| The Offline Wikipedia/Stackexchange project (Kiwix) has similar
| devices for kids classrooms/libraries in rural areas with no
| internet - https://www.kiwix.org/en/downloads/kiwix-hotspot/
| shubhamjain0594 wrote:
| Thanks for this.
|
| I had built [similar
| repository](https://github.com/computationalprivacy/unveil-pi-
| data-colle...) as a part of wifi data capture and visualisation
| experiment ([Project
| UNVEIL](https://github.com/computationalprivacy/unveil-
| deployment)) but it used external antenna.
|
| Any links on how does underlying hardware work to enable
| simultaneous connections?
| lioeters wrote:
| Here's the article which the posted GitHub project is based on.
|
| https://blog.thewalr.us/2017/09/26/raspberry-pi-zero-w-simul...
|
| > At this point, we should be able to connect a device to our
| Raspberry Pi Zero W's AP SSID, while we also have our RPi
| connect to another access point for internet access, and we
| should be able to access the internet from that device through
| our RPi.
|
| The "simultaneous" aspect seems to be achieved by having two
| devices: wlan0 and ap0, the latter created by udev.
| sorenjan wrote:
| Can this be used as a range extender if you use the same SSID and
| password for the access point as the net you're connecting to?
| Would other clients silently roam between the two (or more)
| networks using the same name and password?
| jiggunjer wrote:
| I think it would need to spoof the same MAC as the original AP
| too.
| est31 wrote:
| No, the identification method of an extended service set is
| the SSID, aka the network name. Just set up the same SSID and
| password on both APs, and put them onto the same ip layer
| network. Your device will roam the networks automatically.
| Each AP should get its own MAC otherwise they will think
| packets sent to the other AP was meant for them. WiFi is
| robust enough to deal with noise like e.g. bluetooth, so it
| might survive it, but I doubt it'd support two STAs with the
| same BSSID communicating with each other.
|
| https://en.wikipedia.org/wiki/Service_set_(802.11_network)
| voltagex_ wrote:
| How do you do this with most consumer devices? The only AP
| I've seen do it successfully is the AsusWRT series - Media
| Extender mode seems to be transparent. If I try it with
| anything else I'll end up with two seperate networks, e.g.
| 192.168.8.0/24 connected to 10.1.1.0/24 (I actually have a
| GL.inet AR750S in this configuration right now)
| jonathonlui wrote:
| If you can wire the 2 AP via a LAN, then this is how I've
| used cheap consumer wifi APs which are usually combo
| AP+router devices:
|
| The first AP is connecting to internet gateway through
| its WAN port. This AP does the networking stuff like
| DHCP, NAT, etc.
|
| The other wifi APs are configured to be AP-only, i.e.
| disable DHCP. Use same wifi SSID and auth settings as the
| first AP. Then connect the APs using their LAN ports.
|
| Client devices should now connect to the AP with the best
| signal.
|
| But if the client is already connected to an AP and a
| better-signal AP is available, many clients won't
| automatically connect to the better AP. This is because
| the client don't know that the other AP is the same
| network. So if you move around you may need to trigger
| the client to disconnect and reconnect.
|
| This can be solved with APs that have a "mesh" feature
| which can instruct connected clients to reconnect to a
| better AP in the same network using
| https://en.wikipedia.org/wiki/IEEE_802.11k-2008 but AFAIK
| mesh systems from different manufacturers aren't
| interoperable.
| not_exactly__ wrote:
| I'd like to know this too please :)
| [deleted]
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(page generated 2020-08-23 23:00 UTC)