[TAG] Eth0 debugging

[Bob van der Poel]

John Karns wrote:
> On Thu, 22 Jun 2006, Bob van der Poel wrote:
> 
> 
>> Hi all. I'm having some "odd" connection problems and wondering how to
>> track it down.

<snip>

>> 2. The satellite connection is flaky (my friend has the same system and
>> is NOT having these problems).
> 
> Could be attributable to differences in your respective environments.  I
> would assume that a satellite link is somewhat line of sight.  I could be
> wrong, but if you're surrounded by a lot of trees for example, where there
> is dense foliage between the dish and the satellite, that could affect
> signal strength.

Well ... the friend was running his system direct to a XP box, bu has 
since had a linux box installed which he is using a router. He's 
distributing his connection to some neighbours.

Can we call a sat link at 22500 miles "line of sight"? But, seriously, 
the trees, etc should not be the issue. According to the ISP my SNR 
(signal to noise ratio) is "as good as it gets". No magic trees jumping 
up in the way. Now, really bad weather can effect all this. But, the 
times I'm talking about are not bad weather.

> 
> 
>> 3. I'm having a software problem. Buffer overflows or something. Which
>> means that a reboot would fix it (sometimes it does).
> 
> Depends on what kind of connection protocol - if that's the right
> terminology - your modem uses.  Perhaps one of the easiest to deal with
> is just a plain old ethernet connection, where the port of your modem
> provides a routable IP address.

Yes. I think that is the case here. The IP is dynamic, but I don't think 
it changes very often. Hmmm, could this be a DHCP issue?

>> 4. I'm having a hardware problem with the on board ethernet. Don't know
>> if a soft reboot would effect this, but the power cycle today didn't.
> 
> Always a possibility, although usually of low probability.  The way to
> test for that is with a different host and / or NIC.
> 

Yes, that was one of the ISP's suggestions. I'll have to cobble another 
box together to see. If I have time ...

> Just a WAG on my part, but I would guess that your modem is rather
> similar to ADSL, in that it uses a synchronous connection.  I would
> further guess that the CONNECTED light indicates whether or not the modem
> is synchronized.  In my experience, that's usually where my connection
> problems arise.  Re-initializing the modem usually takes care of that
> issue by forcing connection renogociation with the port on the ISP side.
> 
> To summarize, my procedure is something like this:
> 
> 1) From a terminal command prompt: "ifconfig" to see the status of the
> host network interfaces.  You should see a response something like:
> 
> wlan0     Link encap:Ethernet  HWaddr 00:E0:98:49:85:6D
>           inet addr:192.168.1.116  Bcast:192.168.1.255  Mask:255.255.255.0
>           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>           RX packets:6042 errors:10 dropped:0 overruns:0 frame:10
>           TX packets:6281 errors:0 dropped:0 overruns:0 carrier:0
>           collisions:0 txqueuelen:1000
>           RX bytes:5052344 (4.8 MiB)  TX bytes:955796 (933.3 KiB)
> 
> The wlan0 above is the name that the Linux host is giving to the
> interface.  Yours could be different, such as 'eth0'.  One can also ping
> the local interface to see if it's talking to the host.  In this case
> "ping 192.168.1.116".

Question: WHen pinging the local host like this does the chain leave the 
local box? I'm not sure what this proves other than the fact the IP 
address is valid and correct? Or does it have to go the modem first? 
Which would be an indication that the modem is "active".

> 
> 2) "netstat -nr" should show the gateway address, indicated with a 'UG'
> flag on the same line.  Depending on whether your modem is running bridged
> or as a router (depends on the equipment and the ISPs choice of
> confiuration), this could be an interface on the modem (functioning as a
> router / dhcp server) or an interface that the ISP is providing.  A
> successful ping (a response is echoed to your terminal screen, with a time
> in seconds indicating the latency of the response) to that IP would
> indicate that the problem is outside of your host / modem environment.

Funny that you mention ping (again). Last time I had the problem I tried 
to ping my isp:

bob$ ping xplornet.com
PING xplornet.com (207.179.143.226) 56(84) bytes of data.

--- xplornet.com ping statistics ---
7 packets transmitted, 0 received, 100% packet loss, time 6000ms

At the time I thought this "showed something". Hmmm, later I find that 
the ISP is blocking.

> 
> It may not be conclusive however, because in some cases, the ISP will
> block pings (as mine does).  In that case, you can pick some known
> internet address.  Use a number rather than a name though (such as
> 209.73.186.23 rather than www.yahoo.com), to eliminate DNS issues from
> this step.  If you succeed with the ping to the IP address, but not to the
> name address, then the problem is not a connection issue, but is in name
> resolving - most likely a problem in the ISPs domain.

Yup. Interesting that I can ping the IP gateway from netstat -nr

> 
> 3) Re-init the modem.  Even with a steady-on sync lite, the connection
> status could be flaky, such as might be caoused by a short interruption
> in the power to the modem.
> 
> 4) Depending on your distro (Slakware being an exception, as it uses a
> BSD style init rather than SysV - could be different now though), you can
> try re-initializing the networking subsystem on your host:
> 
> /etc/init.d/networking restart

Mandrake. Yup, tried that without success.

> 
> works on most Debian derived distros, as well as SuSE, IIRC.
> 
> This procedure is not exhaustive, but should help get you started.
> 

Question: would pulling the ethernet cable in/out prove or do anything?

THanks.

-- 
Bob van der Poel ** Wynndel, British Columbia, CANADA **
EMAIL: bvdp at xplornet.com
WWW:   http://users.xplornet.com/~bvdp