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

Flavio Grossi flaviogrossi at ymail.com
Fri Jul 23 05:14:35 EDT 2010


no ideas?



----- 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


      
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