[wplug-bsd] Net configuration still not working

Poyner, Brandon bpoyner at ccac.edu
Wed Jul 13 09:46:55 EDT 2005


> I'm not familiar with the arp command.. but here are the outputs:
> 
> >From the laptop (192.168.1.20, Linux 2.6.8), after setting
> # arp -an
> ? (192.168.1.2) at <incomplete> on eth0
> ? (192.168.1.1) at 00:13:10:19:67:58 [ether] on eth0
> #
> 
> >From the BSD box (192.168.1.2, FreeBSD 5.3)
> # arp -an
> ? (128.2.56.1) at 08:00:7f:01:00:57 on xl0 [ethernet]
> ? (128.2.59.255) at ff:ff:ff:ff:ff:ff on xl0 permanent [ethernet]
> ? (192.168.1.1) at (incomplete) on pcn0 [ethernet]
> ? (192.168.1.2) at 00:60:b0:f0:69:d0 on pcn0 permanent [ethernet]
> #
> 
> -Brandon

Think of arp as being like a routing table at the ethernet level.
Anything on the same subnet will be using arp to discover ethernet mac
addresses in order to communicate.  If you're sending a packet that is
outside of your subnet you need to hand it to a gateway (router) that
resides on your subnet (and is therefore arp-able).  

When you ping an IP on your subnet the first thing it will do is send
out an ARP broadcast and a reply will come back if everything is working
properly, like this:

09:29:22.264177 arp who-has 192.168.0.1 tell 192.168.0.2
09:29:22.264251 arp reply 192.168.0.1 is-at 00:02:43:a3:b3:62

Your computer then adds to the arp table 192.168.0.1 as being
00:02:43:a3:b3:62.  Now it knows the ethernet level address, and will
encapsulate the IP packets inside of an ethernet packet with a
destination of that mac address.  

Ok, so what your output indicates is that things are broken
('incomplete') at the ethernet level between the BSD box and the WRT54GS
(The Linux box can see the WRT54GS).  Most likely you're sending the
'arp who-has' requests but there is no reply.  You can attempt to see
this with the command 'tcpdump -i pcn0 arp'. 

In the process of elimination I'd try using a different ethernet cable,
trying a different ethernet port on the WRT54GS, and getting the WRT54GS
out of the picture.

Brandon Poyner
Network Engineer III
CCAC - College Office
412-237-3086




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