arp-requests cannot be seen by specific nodes
Solution 1
I had the same problem recently. I figured out that AR9271 chipset's have problem on onboard transmitter antenna. If you use an external antenna, then you will not have a problem. And this problem only occurs on ad-hoc mode.
The reason you don't experience problem with the TP-link should be that these modules uses external antenna which overcomes the chipset's problem, and ZCN modules should not have an external antenna.
Solution 2
This could be related to the "hidden node problem" if .6 and .7 aren't in direct radio contact, but without knowing the distances involved it's impossible to say.
Also either or both of the chipsets could have a buggy ad-hoc mode, it's not used much these days and wouldn't be surprising.
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johan
Updated on September 18, 2022Comments
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johan over 1 year
I create an open ad-hoc wlan by using
iwconfig
(I have the same issue withwpa_supplicant
as well). there are 4 nodes on the network as seen on the figure below. The nodes run ubuntu 12.04 and debian squeeze, and have 3.7.1, 3.5 and 3.2 kernels. I use two different usb dongle brands (TP link and ZCN) that all have AR9271 chipset andath9k_htc
driver (here is lsusb output and ethtool output).The problem I am experiencing is that two nodes (
10.0.0.2
and10.0.0.5
) which have TP link usb wifi dongles can ping any node on the network, and vice-versa. However, the other nodes (10.0.0.6
and10.0.0.7
) that have ZCN wifi dongle cannot ping each other, but they have no problem communicating with TP-link wifi modules.tcpdump
shows that10.0.0.6
and10.0.0.7
cannot see their arp-request, e.g.20:37:52.470305 ARP, Request who-has 10.0.0.7 tell 10.0.0.6, length 28 20:37:53.463713 ARP, Request who-has 10.0.0.7 tell 10.0.0.6, length 28 20:37:54.463622 ARP, Request who-has 10.0.0.7 tell 10.0.0.6, length 28 20:37:55.472868 ARP, Request who-has 10.0.0.7 tell 10.0.0.6, length 28 20:37:56.463439 ARP, Request who-has 10.0.0.7 tell 10.0.0.6, length 28 20:37:57.463469 ARP, Request who-has 10.0.0.7 tell 10.0.0.6, length 28
but they are able to see and get reply from TP-link's modules.
20:39:23.634459 ARP, Request who-has 10.0.0.2 tell 10.0.0.6, length 28 20:39:23.634551 ARP, Reply 10.0.0.2 is-at 64:70:02:18:d4:6a (oui Unknown), length 28 20:39:23.636687 IP 10.0.0.6 > 10.0.0.2: ICMP echo request, id 572, seq 1, length 64 20:39:23.636809 IP 10.0.0.2 > 10.0.0.6: ICMP echo reply, id 572, seq 1, length 64 20:39:24.635497 IP 10.0.0.6 > 10.0.0.2: ICMP echo request, id 572, seq 2, length 64 20:39:24.635558 IP 10.0.0.2 > 10.0.0.6: ICMP echo reply, id 572, seq 2, length 64 20:39:28.651946 ARP, Request who-has 10.0.0.6 tell 10.0.0.2, length 28 20:39:28.654021 ARP, Reply 10.0.0.6 is-at 00:19:70:94:7c:8b (oui Unknown), length 28
My question is that what could be the reason that
10.0.0.6
and10.0.0.7
cannot see thearp-request
that they send each other? How can I find out the problem?If I add couple more nodes with ZCN wifi dongle on the network, these nodes are also not able to talk with each other, but they are fine with TP-link. Or if I swap the wifi modules, the nodes with ZCN have always problem but TP-link modules are fine.
here is the
/etc/network/interfaces
,ifconfig
,iwconfig
,ip a
,ip r
,route
outputsEDIT: I was suspecting if the problem is
arp_filter
related but/proc/sys/net/ipv4/conf/*/arp_filter
is0
on the all subdomains(*). If I add arp info of10.0.0.6
and10.0.0.7
manually on these nodes,tcpdump
andwireshark
does not show that they sendping
to each other. If Iping
the broadcast address (10.0.0.255 in my case),10.0.0.6
and10.0.0.7
are able hear it.EDIT2: Here is pcap files http://filebin.net/6cle9a5iae from
10.0.0.6
(ZCN module),10.0.0.7
(ZCN module), and10.0.0.5
(TP-link module that does not have problem). here is the ping outputs from10.0.0.6
http://pastebin.com/swFP2CJ9 I captured the packages simultaneously. The link also includesifconfig
;iwconfig
; anduname- a
outputs for each node.-
Mircea Vutcovici about 11 yearsCan you make a network capture of the ARP traffic on both 10.0.0.6 and 10.0.0.7 machines at the same time? Use tcp dump and share it as a pcap file.
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johan about 11 yearsThank you Mircea Vutcovici, please see the EDIT2 for the pcap files. Please let me know if you would like to have more information.
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poige about 11 yearsWell, you can try using static ARP and see how/if it changes the connectivity problem.
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Flup about 11 yearsCould you post a dump of the traffic from a wireless sniffer tool like
kismet
? This will include the 802.11 headers in case there's something odd about them. -
johan about 11 yearspoige, I did add static ARP on the nodes but the problem remained.
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johan about 11 yearsFlup, I have not used kismet before, but I will try to figure out how to use it. Do you prefer any specific format or flag on kismet capturing?
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Flup about 11 yearsIt's a wee while since I've used it, but you should be able to get it to write a pcap file, then read that file with wireshark and post the results.
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Florian Haider about 11 yearsgiven the issues you are having with the ZCN dongles, and your requirement to have the clients all talk directly to each other on the network I would just throw them out and replace with the TPLink dongles that actually work on your network. Or it could be a driver issue with the ZCN adapters - try another.
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