Network problem
Bob Chiodini
rchiodin at bellsouth.net
Wed Feb 23 12:22:19 UTC 2005
On Wed, 2005-02-23 at 02:11 +0100, Mats Erlandson wrote:
> Gentlemen,
>
> I have stopped the machine, removed the second ethernet card, rebooted
> and in that process, through kudzu, removed the configuration for the
> removed card. After system is up, I have verified that the
> configuration files for card two are removed. I am now back to where I
> was after having tried, for several hours, to get eth0 to talk to the
> switch. The green lights are on at either and, the cable check on the
> switch shows cable OK. The computer can talk to the other
> computers/devices on the local network but cannot even ping the switch.
> I am logged into the computer from my laptop (using ssh) and it works fine.
>
> The 'netstat -rn' output is now;
> Kernel IP routing table
> Destination Gateway Genmask Flags MSS Window irtt
> Iface
> 192.168.0.0 0.0.0.0 255.255.255.0 U 0 0 0
> eth0
> 169.254.0.0 0.0.0.0 255.255.0.0 U 0 0 0
> eth0
> 0.0.0.0 192.168.0.1 0.0.0.0 UG 0 0 0
> eth0
>
> and 'ifconfig' is;
> eth0 Link encap:Ethernet HWaddr 00:0F:EA:5C:06:CF
> inet addr:192.168.0.90 Bcast:192.168.0.255 Mask:255.255.255.0
> UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
> RX packets:785 errors:0 dropped:0 overruns:0 frame:0
> TX packets:269 errors:0 dropped:0 overruns:0 carrier:0
> collisions:0 txqueuelen:1000
> RX bytes:231079 (225.6 KiB) TX bytes:27185 (26.5 KiB)
> Interrupt:201 Base address:0xc000
>
> What is so strange, is that the computer can talk to all local addresses
> except the switch (192.168.0.1) and two other computers on the local
> network can talk to it, all obviously through the switch both ways.
> This shows that the cabling is OK, and that the problem is probably in
> the routing on the computer (not allowing it to connect directly to the
> switch) or in the switch, not accepting communication from the
> computer. The switch routes properly for the other computers on the
> network and can be managed from either one (tested) but not from the
> problem child. If I change the configuration on the computer to use
> DHCP (and rebooting) the computer does not get (receive/accept) the DHCP
> configuration and is thus 'dead', i.e. no communication to nor from any
> computer. Therefore, until the communication to/from the switch is OK I
> am using a static address. To eliminate hardware faults possible in the
> ethernet port on the motherboard (eth0) I installed a network card,
> tested to perform OK in another computer, and disabled the motherboard
> port using the BIOS. With only an expansion ethernet card active in the
> computer I made the same tests with the same results. This seems to
> eliminate network card problem in the computer. My current setup is, as
> per the first paragraph above, motherboard ethernet port only with
> static address. Still no joy. I am at a loss.
>
> Regards,
> Mats
>
> Rick Stevens wrote:
>
> > Mats Erlandson wrote:
> >
> >> Well, I did what you suggested, but, to no avail. The result is
> >> still the same. By the way, the reason I put in the second card was
> >> to be able to switch between two, which I already tried without
> >> success. The vexing question is though that if I configure one or
> >> both of the network interfaces for DHCP neither one picks up the DHCP
> >> info. This works flawlessly on both the other computers.
> >>
> >> So, this new computer cannot communicate with the switch or the wide
> >> area network through the switch, but, mysteriously, it can
> >> communicate with other computers/devices on the local area network
> >> routed through the switch.
> >>
> >> A feeling is that the switch is at fault. However, the hardwired
> >> working computer does not mind a port switch on the router, it just
> >> works, also after reboot. The switch must have taken a serious
> >> dislike to the new computer :-).
> >
> >
> > The trick is that you only want ONE NIC. Your routes are confused. In
> > general, there should only be ONE route for each network and you had
> > two. There should also only be one default route (shown as "UG" in the
> > "flags" column of the "netstat -rn" listing).
> >
> > You should also keep in mind that what you think is eth0 may be eth1 and
> > vice versa. Generally, the NIC furthest from the CPU in your
> > motherboard is eth0, but not always (it depends on how the PCI bus
> > probes out). If your motherboard has a built-in NIC, then it's usually
> > eth0.
> >
> > I'd recommend you delete the file
> >
> > /etc/sysconfig/network-scripts/ifcfg-eth1
> >
> > Then edit the file
> >
> > /etc/sysconfig/network-scripts/ifcfg-eth0
> >
> > Since you will be using DHCP, you only need the following information in
> > it:
> >
> > DEVICE=eth0
> > ONBOOT=yes
> > BOOTPROTO=dhcp
> >
> > Also edit the "/etc/sysconfig/network" file and make sure you do NOT
> > have a "GATEWAY=" line in it (your DHCP server will provide one).
> >
> > Next, enter the two commands:
> >
> > /etc/rc.d/init.d/network stop
> > /etc/rc.d/init.d/network start
> >
> > Verify that you have a link between eth0 and your hub/switch/router
> > (they should both have a green LED showing). The cable on the other NIC
> > should be unplugged, just so you don't get confused.
> >
> > Once that's done, verify that eth0 came up and got an IP address:
> >
> > ifconfig eth0
> >
> > You can also verify that the default route got set up. "netstat -rn"
> > should only show a couple of lines. The "device" column should only
> > have "eth0" in it. If "eth1" shows up, we have other issues.
> >
> > You should also check the contents of the "/var/log/messages" file as
> > well as the output of the "dmesg" command to see if you're getting
> > errors on the system setup.
> >
> > As far as "switching" NICs, I assume you mean as a failover method.
> > Doing that manually is not necessarily a good idea. You'd need to bring
> > down the "failed" NIC, destroy existing routes, purge ARP tables, then
> > bring up the second NIC and wait for it to build routes. You can't do
> > it "on the fly".
> >
> > There is a mechanism called "bonding" that allows you to tie the two
> > NICs into a failover service. Linux has a bonding driver, but to make
> > it work the hub/switch/router must also support support bonding. Very
> > few (if any) SOHO (small home or office) units out there (e.g. D-Link,
> > Linksys, AirLink) do. You'd need to go to a relatively high-end switch
> > (3Com, Cisco, Extreme or HP) to get bonding support--and even then it's
> > not that reliable (at least not on HP or 3Com) in my experience.
> > ----------------------------------------------------------------------
> > - Rick Stevens, Senior Systems Engineer rstevens at vitalstream.com -
> > - VitalStream, Inc. http://www.vitalstream.com -
> > - -
> > - Tempt not the dragons of fate, since thou art crunchy and taste -
> > - good with ketchup. -
> > ----------------------------------------------------------------------
> >
> >
>
Are you getting your IP address from the DHCP server running on the
DI-624 router? If not try it or move your IP address within the DHCP
range of the router (default is 100-199).
This is a shot in the dark.
Also, verify that the router is not filtering your IP or MAC.
Bob...
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