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List:       gentoo-user
Subject:    Re: [gentoo-user] eth0 problem - how to find out.
From:       GBloomberg <fin.ack () gmail ! com>
Date:       2004-06-30 6:07:35
Message-ID: 28ca269704062923076c70d382 () mail ! gmail ! com
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On Tue, 29 Jun 2004 23:22:09 -0600, Joseph <syscon@interbaun.com> wrote:
> Both computers are connected to via a switch to a firewall.
> I tried to reproduce the problem: taking down firewall for few minutes but everything worked normally.
> I might never know what had happened, I think I'll need to monitor the connection.

Could be allot of things. I would periodically look at the output
below on both the firewall interface and the Gentoo server interface
for any errors or colisions, drops.. ect..:
****************************
root@fusion Desktop # ifconfig eth1
eth1      Link encap:Ethernet  HWaddr 00:04:03:6F:70:9B
         inet addr:10.0.0.1  Bcast:10.0.0.255  Mask:255.255.255.0
         UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
         RX packets:873819 errors:0 dropped:0 overruns:0 frame:0
         TX packets:1087995 errors:0 dropped:0 overruns:0 carrier:0
         collisions:0 txqueuelen:1000
         RX bytes:122401668 (116.7 Mb)  TX bytes:913442172 (871.1 Mb)
         Interrupt:20 Base address:0x7000
*******************
Could be a duplex issue. Could be a faulty nic. Could be faulty
cabling. Could be a cheap ass switch or bad switch port. Could be a
physical loop in the cabling that causes some kind of firewall rules
to stop traffic for a specific ip because it appears spoofed because
of looping..making it appear that an interface isn't working. When in
reality the firewall is just dropping all traffic form the particular
ip..  happens all the time.

Its just a matter of isolation.
As a start You should check "dmesg" after boot up. You will find a
Duplex negotiation going on. Sometimes two ends both try to
auto-negotiate and there's issues.
Usually the quickest way to isolate the issue as a test would be by
connecting the firewall interface and the other Gentoo server
interface directly together via a crossover cable. Start pushing some
traffic and watch see what if you get any "collisions, errors,
drops... ect..ect.." in you "ifconfig <dev>" output.
This will rule out the switch immediately as the culprit or not and
cabling since your using a crossover versus a straighthrough cable.

Either way. The problem will be very apparent now or you will be that
much closer to isolating the actual cause of the problem. Check your
firewall logs to see if its dropping traffic from that ip.

HTH's

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