Dual Wifi cards on an Alix2D2



  • Hi, i am setting up a site to site wifi link(about 400ft away clear line of sight) with 13dBi panel antennas running on Alix2D2 boards. Given the fact that there are 2 MiniPCI slots i assumed i could run multiple AP's ie. one for the the point to point and one for the local area on each end(internet access is only available at the one site). I am using 4 EMP-8602+S High Power 802.11a/b/g miniPCI Radio Cards total(2 each), the point to point was easy enough to set up but setting up the second card to serve local wifi on each site is proving to be difficult. my clients are being served a DHCP address, the local gateway and DNS are in there but it appears there is no actual conectivity ie. unable to ping through and cannot browse pages even the pfsense page. This is the situation on both ends so i dont think its an isolated problem. so i think its either

    1. Alix 2D2 doesnt support dual wifi cards or,

    2. crappy wifi cards

    After doing some reading i have seen plenty of bad things about these cards, and upon closer inspection i noticed a huge amount of in/out errors in the interface page. any ideas of where to start diagnosing?




  • I'm not a radio engineer but two things I would look at:

    1. Are the channels in use widely separated? (e.g. 1 on one card and 11 on the other).

    2. Are the antennae placed and oriented to minimise the transmit energy going into the other antenna?

    What is reported when a client computer attempts to ping the pfSense LAN interface by IP address? by hostname?



  • The channels being used are 1,6,11 so yes as much separation as possible.
    The two antennas for local wifi are about 5" apart.
    Same reply to hostname as to ip, no reply.

    I am using 1.2.3release and I think I am going to upgrade to 2rc3, I have a funny feeling it's a driver issue. It does everything as normal except give me network access, which is why I'm so confused. Also i still can't get a clear answer, does pfsense support multiple wifi cards on alix Platform? Thanks



  • Another question came to mind. I have about 8' of lmr400 on one end of the point to point connection and about 80' on the other end, does any configuration need to change for optimal performance?



  • @jgleadall:

    Also i still can't get a clear answer, does pfsense support multiple wifi cards on alix Platform? Thanks

    The pfSense software supports multiple WiFi cards. I have, at times, run a PCI and a USB WiFi card concurrently on my pfSense box.

    I have no experience with Alix. There might be some Alix specific thing that makes it difficult to run two high power mini-PCI WiFi cards on the same board.

    You didn't answer my question about antenna orientation.

    Edit 1:
    @jgleadall:

    my clients are being served a DHCP address, the local gateway and DNS are in there but it appears there is no actual conectivity

    I presume you have verified that the client gets the correct DHCP address, gateway and DNS.

    Have you checked the firewall log and system log during those access attempts from local WiFi client? How is your bridge and its member interfaces configured with firewall rules? (To get DHCP working you must have added some firewall rule.) Have you setup a ping on a client to the local pfSense IP address and started a packet capture on pfSense to verify the ping is being received and a response generated.

    Have you exchanged the roles of the two WiFi cards at one site to see if the lack of connectivity is an attribute of the card or the role?



  • The antenna orientation is two 5 dBi rubber duck antennas side by side about 4-5" apart, and an N connector for the panel antennas a few inches away from them.

    I have verified the DHCP info my clients are correct, they are the same as when plugged into the lan

    There are no firewall logs showing anything to do with the 2nd wifi interface

    I have exchanged wifi cards and they all work the same.

    The WiFi and Lan interfaces have allow all firewall rules

    I have not setup a ping on a client to the local pfSense IP address and started a packet capture on pfSense to verify the ping is being received and a response generated. But i plan to, i should have thought of that sooner.

    I do however wonder if this might be a power thing, alix boards draw very little power, but who knows the 2nd minipci card could be starved, not really sure how that works.

    I forgot to say thanks thus far, your advice is much appreciated



  • Here are some pics of the units if that helps






  • @jgleadall:

    I have verified the DHCP info my clients are correct, they are the same as when plugged into the lan

    Its curious that the client computers and pfsense can exchange DHCP packets but not pings!

    @jgleadall:

    I have exchanged wifi cards and they all work the same.

    So a card that is known to work on the ptp link doesn't work as the local AP and vice versa. This would seem to rule out a fault in the cards.

    Does the AP work if the ptp link is disabled? or if the ptp card is removed?

    @jgleadall:

    I do however wonder if this might be a power thing, alix boards draw very little power, but who knows the 2nd minipci card could be starved, not really sure how that works.

    Great thought. I tend to just assume power will be ok. It might be that power is chained from one miniPCI socket to the other, resulting in a lower voltage at the tail end card. That might be difficult to check without specialised connectors.

    It would be worth asking pcengines (designers of Alix) about power on the miniPCI sockets and particularly about power for the cards you are using.

    It might also be worth investing in a cheap USB WiFi NIC (e.g. Tenda W311U or TP-Link TL-WN321G, under US$15 where I live) to test for the role of AP for the client computers. It is not obvious to me there is any benefit in having a high power WiFi card acting as AP for a bunch of client computers most of which won't have high power interfaces. If you need high power to get from AP to client won't you also need high power to get from client to AP (assuming roughly equivalent receiver sensitivities)?



  • Yes that is very curious, whats even more is that when a windows client connects the little icon with 5 bars is shown for a good 5 seconds before the icon changes to one that shows there is no internet access, and no windows firewall is not on. I think i need to check the system log files for hardware errors maybe?

    Dont quote me on this, but i think it did work for a brief period in initial testing now that you mention it, having the ptp link disabled. I am going back out to the site this afternoon to try and fix the local wifi and i will give this a shot and watch the logs a little more carefully when i switch things around and then enable both to see if anything pops up. Do you think it would have been better do use 2 differnt types of cards rather than the same? i hope they arent trying to use the same IRQ or somthing like that.

    Is my antenna placement acceptable? i wonder if running 2 antennas off the one card might be causing some problems?

    I got an email back from the guys at Xagyl where i bought all the hardware from and they seem to think there is no problems with power, under 4w of consumption which is peanuts i think.

    I will pick up a usb wifi stick today for testing, that is a good idea.

    About the high power cards, when i first purchased them i was under the impression that more is  better, after doing some research though I've found the opposite to be true. Yes, power needs to be matched on both ends to to take advantage of all that power and really anything in the ~200mw range would have been more than acceptable since few clients are more powerful than that.



  • @jgleadall:

    Do you think it would have been better do use 2 differnt types of cards rather than the same? i hope they arent trying to use the same IRQ or somthing like that.

    For years now FreeBSD drivers have been written to allow interrupt sharing and multiple instances of the same device. I think its unlikely you would have trouble in either of those areas.

    @jgleadall:

    Is my antenna placement acceptable? i wonder if running 2 antennas off the one card might be causing some problems?

    It shouldn't be a problem if the card was designed for two antennae and you have connected them up properly.

    Again, I'm not a radio engineer but I suspect you could be having some problems due to having a receiver quite close to a transmitter in the same box. Are the connections from the card to the antenna connectors shielded? It probably won't matter if there was only one card in the box but might with two cards.

    @jgleadall:

    I got an email back from the guys at Xagyl where i bought all the hardware from and they seem to think there is no problems with power, under 4w of consumption which is peanuts i think.

    4W is peanuts on a "standard" PC but it might be a problem on a system that only consumes about 5W without the cards. Is that 4W (max) per card or for two cards? Is that average of 4W or 4W when transmitting? Worst case would probably be both cards transmitting concurrently.

    @jgleadall:

    About the high power cards, when i first purchased them i was under the impression that more is better, after doing some research though I've found the opposite to be true. Yes, power needs to be matched on both ends to to take advantage of all that power and really anything in the ~200mw range would have been more than acceptable since few clients are more powerful than that.

    More is often better, at least up to the point where more is more than you need. Consider food.



  • so i just got back from the site a couple of hours ago. here are my findings:

    I did a dmesg in the command prompt and noticed that the ath0 and ath1 section mentioned something about watchdog not working, cant remember exactly but i googled it and sure enough somebody referenced that error with driver issues. After seeing that i decided i would be stupid not to run the 2.0RC3 upgrade. 10 minutes later and all was well, everything was working correctly and no errors and best of all the local wifi was working like a charm. The only thing that was slightly botched was a default route that didnt quite work right and needed to be changed, but other than that it was seemless. I was hesitant to use 2.0 because of some problems i had with it about a year ago, they seem to be cleared up now though works like a charm.

    As of now the point to point radios are turned down to something like 20%. I did another throughput test and windows to windows file transfer gave me only about 1.2MB/sec even though the link negotiated at 54mbps. As i mentioned before these 2 35deg 13dBi panel antennas are in direct line of sight, polarized correctly and are aimed as best i can. Does this sound normal for longer distance links? i had the power all the way up before and that didn't seem to make much of a difference in throughput and i would assume only gave me more in/out errors. there are a few other wifi networks in the area, my thought is they are making some noise and perhaps limit the throughput by introducing more errors. I have honestly never had any good throughput on wireless networks so im not really sure what to compare this too.



  • Glad you got it working and so simply.

    @jgleadall:

    I did another throughput test and windows to windows file transfer gave me only about 1.2MB/sec even though the link negotiated at 54mbps.

    Thats about the  best I have seen on my home network for transfers between two Linux systems on separate subnets.
    http://en.wikipedia.org/wiki/IEEE_802.11 suggests 22Mbps is the best data throughput you are likely to see on a 54Mbps WiFi link. Actual data throughput will depend heavily on error rates.



  • Interesting, so does the fact that they are on separate networks have anything to do with it i wonder?



  • Sorry to undig this post
    I am having some problems with an alix 2c2(older model) the signal on the cards is not constant.
    Tips i tried may help:
    -Try to disable diversity on the network cards and find the one you have the pigtail attached to.
    -Try different regulatory domains or country settings .
    -Try the B and G mode just to try to find a cause.


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