Networking problem

sdawalt at sdawalt at
Sun May 15 15:41:29 UTC 2011

Quoting JD <jd1008 at>:

>>     Usually, firewalls don't inhibit ARP entries. To test this theory,
>> try "ping" from your box.  Directly after
>> that, issue the command "arp -a".  If ARP works, you should see
>> something like this.
>> ? ( at 00:30:ab:13:9e:3d [ether] on eth0
>> (On my net, is my gateway.)  If it doesn't work, you'll see
>> something like this:
>> ? ( at<incomplete>  on eth0
>> where is a non-existent machine on my network.  And you'll
>> see ping responses such as these:
>> PING ( 56(84) bytes of data.
>>   From icmp_seq=2 Destination Host Unreachable
>>   From icmp_seq=3 Destination Host Unreachable
>>   From icmp_seq=4 Destination Host Unreachable
>>     You've already posted something like this, so it's a good bet ARPs
>> aren't working.  So the wireless router is a good bet at this point.
>>     Shane
> On the Fedora Machine:
> # arp -a
> ? ( at 0:1d:1a:00:91:c1 [ether] on wlan0
> On the PowerBook Machine:
> # arp -na
> ? ( at 0:28:fe:6:ef:7 on en1 [ethernet]
> ? ( at (incomplete) on en1 [ethernet]
> ? ( at 0:1d:1a:00:91:c1 on en1 [ethernet]
> ? ( at ff:ff:ff:ff:ff:ff on en1 [ethernet]
> Now this is really strange!
> Fedora's arp reports only the gateway!
> Whereas PowerBooks arp reports the gateway, the wired machine
> and even the Fedora machine it cannot ping:

    Keep in mind that the table shown above from the powerbook doesn't  
say it is reporting the Fedora machine.  The powerbook is reporting  
that it attempted to obtain the MAC address for the host at, but it didn't receive a reply.  A classic indication of  
a broken layer-2 LAN path.  Since both machines are wireless, it lends  
credence to the theory that the router is blocking inter-host  
communication.  (Nothing more effective than not passing ARP  
broadcasts to isolate hosts.)  Start looking at the wireless config on  
the wireless router; particularly it's client hiding.  Surely that can  
be turned off.  But don't pursue static or default route issues until  
you can ping between LAN-connected hosts.

   As far as ad-hoc; I don't know.  I use infrastructure mode if for  
nothing else than deterministic operation.  Having everybody connect  
with everybody else in the air just sounds massively chaotic ... and  
networks are chaotic enough at times.


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