Single (hostap) node on an ad-hoc network never receives ARP requests

Freek de Kruijf f.de.kruijf at gmail.com
Fri Jul 23 05:47:37 EDT 2010


On Friday 23 July 2010 11:14:35 Flavio Grossi wrote:
> no ideas?

Maybe the ARP goes to a different interface on K.
So try to tcpdump all packages on all interfaces or use wireshark on all 
interfaces. 

> ----- Messaggio originale -----
> Oggetto: Re: Single (hostap) node on an ad-hoc network never receives ARP
> requests
> 
> Update: i found the same problem using the UDP protocol in broadcast mode:
> I cannot receive broadcast messages sent by this device. With tcpdump i
> see datagrams leaving the device, but on my laptop i never receive
> anything. The other way round (laptop transmits and the device listens),
> everything is good.
> 
> 
> So the problem seems to be with broadcast requests made by the Ambicom
> wireless card (hostap driver).
> Any ideas? What can i do to debug this problem?
> 
> 
> ----- Messaggio originale -----
> Oggetto: Single (hostap) node on an ad-hoc network never receives ARP
> requests
> 
> i need help debugging a problem i have with a small device
> (http://www.k-team.com/mobile-robotics-products/khepera-iii) using an
> Ambicom WL1100C-CF compact flash wireless card, using the hostap driver
> from 2.6.23 or 2.6.25 kernel (cannot upgrade kernel, since it needs some
> vendor-specific patches).
> 
> I'm trying to set up a wireless ad-hoc network with my laptop (L from now
> on, ip 192.168.0.100) and this device (K from now on, ip 192.168.0.1), and
> everything is well configured (details below).
> 
> The problem is I cannot reach L from K using ping, unless i first ping from
> L to K (ping L -> K always works fine).
> 
> Using tcpdump i found that the problem is in the ARP protocol: when i ping
> L from K, i can see ARP requests
> 
> 192.168.0.1$ tcpdump -i wlan0
> listening on wifi0, link-type IEEE802_11 (802.11), capture size 68 bytes
> 00:13:40.596617 arp who-has 192.168.0.2 tell 192.168.0.1
> 00:13:41.596303 arp who-has 192.168.0.2 tell 192.168.0.1
> 00:13:42.596174 arp who-has 192.168.0.2 tell 192.168.0.1
> 00:13:43.626226 arp who-has 192.168.0.2 tell 192.168.0.1
> 00:13:44.626234 arp who-has 192.168.0.2 tell 192.168.0.1
> 
> but the destination never receives the request, and never answer it, so the
> communication cannot begin:
> 
> 192.168.0.2$ tcpdump -i wlan0
> listening on wifi0, link-type IEEE802_11 (802.11), capture size 68 bytes
> [no output]
> 
> 
> 
> Ping from L to K works fine (i can see ARP requests and answers). After a
> successfull ping in this direction, K already has the MAC address in his
> ARP table, and ping from K to L works good.
> 
> 
> Below you can see my network configuration.
> Can you help help me with this? What can i do to understand where the
> problem is?
> 
> 
> 192.168.0.1$ ifconfig
> wlan0     Link encap:Ethernet  HWaddr 00:10:7A:71:9B:C1
>           inet addr:192.168.0.1  Bcast:192.168.0.255  Mask:255.255.255.0
>           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>           RX packets:31 errors:0 dropped:0 overruns:0 frame:0
>           TX packets:34 errors:0 dropped:0 overruns:0 carrier:0
>           collisions:0 txqueuelen:0
>           RX bytes:4470 (4.3 KiB)  TX bytes:6267 (6.1 KiB)
>           Interrupt:77
> 192.168.0.1$ iwconfig
> wlan0     IEEE 802.11b  ESSID:"roboMANET"  Nickname:""
>           Mode:Ad-Hoc  Frequency:2.412 GHz  Cell: 4E:B2:E2:90:3A:98
>           Bit Rate:2 Mb/s   Sensitivity=1/3
>           Retry short limit:8   RTS thr:off   Fragment thr:off
>           Encryption key:off
>           Power Management:off
>           Link Quality=55/70  Signal level=-24 dBm  Noise level=-80 dBm
>           Rx invalid nwid:0  Rx invalid crypt:2  Rx invalid frag:0
>           Tx excessive retries:9  Invalid misc:12   Missed beacon:0
> 192.168.0.1$ route
> Kernel IP routing table
> Destination     Gateway         Genmask         Flags Metric Ref    Use
> Iface 192.168.0.0      *               255.255.255.0   U     0      0     
>   0 wlan0
> 
> 
> laptop$ ifconfig
> wlan0     Link encap:Ethernet  HWaddr 00:16:ea:37:c9:ba
>           inet addr:192.168.0.100  Bcast:192.168.0.255  Mask:255.255.255.0
>           inet6 addr: fe80::216:eaff:fe37:c9ba/64 Scope:Link
>           UP BROADCAST MULTICAST  MTU:1500  Metric:1
>           RX packets:0 errors:0 dropped:0 overruns:0 frame:0
>           TX packets:10 errors:0 dropped:0 overruns:0 carrier:0
>           collisions:0 txqueuelen:1000
>           RX bytes:0 (0.0 B)  TX bytes:976 (976.0 B)
> laptop$ iwconfig
> wlan0     IEEE 802.11abgn  ESSID:"roboMANET"
>           Mode:Ad-Hoc  Frequency:2.412 GHz  Cell: 4E:B2:E2:90:3A:98
>           Tx-Power=15 dBm
>           Retry  long limit:7   RTS thr:off   Fragment thr:off
>           Encryption key:off
>           Power Management:off
> laptop$  route
> Kernel IP routing table
> Destination     Gateway         Genmask         Flags Metric Ref    Use
> Iface 192.168.0.0      *               255.255.255.0   U     0      0     
>   0 wlan0

-- 
fr.gr.

Freek de Kruijf


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