Quick dual-homed networking question...

WeNdeL · 05-21-2003, 10:40 AM

I know the answer to this is probably very simple, yet for some reason it escapes me...

I am trying to configure a box to communicate to two seperate networks. No IP forwarding is needed. Here is the routing table:

Code:

[root@bigbrother network-scripts]# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.2.0     0.0.0.0         255.255.255.0   U     0      0        0 eth1
192.168.10.0    0.0.0.0         255.255.255.0   U     0      0        0 eth0
127.0.0.0       0.0.0.0         255.0.0.0       U     0      0        0 lo
0.0.0.0         192.168.2.254   0.0.0.0         UG    0      0        0 eth1

I cannot ping the 192.168.10.0 network. I have tried adding a gateway to this routing table which then looks like this:

Code:

[root@bigbrother network-scripts]# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.2.0     0.0.0.0         255.255.255.0   U     0      0        0 eth1
192.168.10.0    192.168.10.3    255.255.255.0   UG    0      0        0 eth0
192.168.10.0    0.0.0.0         255.255.255.0   U     0      0        0 eth0
127.0.0.0       0.0.0.0         255.0.0.0       U     0      0        0 lo
0.0.0.0         192.168.2.254   0.0.0.0         UG    0      0        0 eth1

The ifcg-eth0 file is like so:

Code:

[root@bigbrother network-scripts]# cat ifcfg-eth0
DEVICE=eth0
ONBOOT=yes
BOOTPROTO=static
IPADDR=192.168.10.3
NETMASK=255.255.255.0
NETWORK=192.168.10.0

The only hardware issue I can see is that the NIC card *could* be bad. I don't think so at the moment...

Any ideas what might be the problem?

david_ross · 05-21-2003, 12:50 PM

Here are a few things to check:

1) Can you ping 192.168.10.3 from the machine itself?
2) Do all link lights look OK?
3) If this is 2 machines connected directly - is a crossver cable used?
4) What is your network layout?

Code:

       [Server in question]
           /           \
          /             \
       [PC1]           [PC2]

OR

       [Server in question]
          /           \
         /             \
      [HUB1]         [HUB2]
      /    \         /    \
     /      \       /      \
  [PC 1]   [PC 2] [PC 3]  [PC 4]

WeNdeL · 05-21-2003, 01:58 PM

ok... well...

1) Yes

2) Links are ok, after some more testing, I know the card is fine as is the cable.

3) I am basically making a test environment to set up ntop within in a switch. So, the box has one NIC connected to a switch and the other NIC is connected to a DIFFERENT switch that has only two other machines connected to it. Those two can see each other just fine.

4)

Code:

          
                 [ switch1 ]                [ switch 2 ]
                      |                      /    |    \
                      |                     /     |     \
                [ problem box ] -----------/      |     [ 192.168.10.1 ]
                192.168.2.114                     |
                192.168.10.3              [ 192.168.10.2 ]

The weird thing is this.... this is killin me...

I have tried turning both interfaces off. Bringing up just one of them at a time on the 192.168.2.0 network. Both interfaces worked when placed on the 192.168.2.0 network found in switch 1. When I tried the same on the other network/switch, no luck.

I even brought both interfaces up on the 192.168.2.0 network at the same time and they both worked.

Bringing up a damn interface should be cake. I have never run into this before. I am about stumped...

david_ross · 05-21-2003, 02:13 PM

What command did you use to add the route? Did you specify it as a network using "-net"?

dorian33 · 05-21-2003, 02:30 PM

till now I have no idea but post the results of ifconfig output....

WeNdeL · 05-21-2003, 02:36 PM

route add -net 192.168.10.0 netmask 255.255.255.0 gw 192.168.10.3

Code:

[root@bigbrother root]# ifconfig -a
eth0      Link encap:Ethernet  HWaddr 00:10:5A:15:BD:AE
          inet addr:192.168.10.3  Bcast:192.168.10.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:1490 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1017 errors:0 dropped:0 overruns:0 carrier:157
          collisions:0 txqueuelen:100
          RX bytes:127547 (124.5 Kb)  TX bytes:88056 (85.9 Kb)
          Interrupt:10 Base address:0xd000

eth1      Link encap:Ethernet  HWaddr 00:A0:C9:A5:0D:52
          inet addr:192.168.2.114  Bcast:192.168.2.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:8865568 errors:0 dropped:0 overruns:0 frame:0
          TX packets:6853185 errors:0 dropped:0 overruns:185 carrier:0
          collisions:0 txqueuelen:100
          RX bytes:1328503763 (1266.9 Mb)  TX bytes:3170224632 (3023.3 Mb)
          Interrupt:11 Base address:0x5000

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:423894 errors:0 dropped:0 overruns:0 frame:0
          TX packets:423894 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:124900214 (119.1 Mb)  TX bytes:124900214 (119.1 Mb)

david_ross · 05-21-2003, 02:40 PM

As far as I can see that should work fine. Do you have an objection to using 2 ip ranges - ie use 172 addresses for machines on the second switch. It makes the routing a little easier to manage.

manthram · 05-21-2003, 02:41 PM

Quote:

Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
192.168.2.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1
192.168.10.0 192.168.10.3 255.255.255.0 UG 0 0 0 eth0
192.168.10.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
127.0.0.0 0.0.0.0 255.0.0.0 U 0 0 0 lo
0.0.0.0 192.168.2.254 0.0.0.0 UG 0 0 0 eth1

i see you added the route for the network. but in the third line there is route for that network saying that the gateway is 0.0.0.0 i.e. the default gateway. delete that route and then try pinging.

WeNdeL · 05-21-2003, 02:45 PM

STOP! Hold the presses...

To troubleshoot this a little we moved all three of these machines to the second switch. They could all talk to eachother...

So the problem lies in the switch... but where...

/me scratches head

Thanks for you're help thus far by the way...

david_ross · 05-21-2003, 02:46 PM

Did you have the server plugged into the uplink port?

WeNdeL · 05-21-2003, 03:21 PM

nope... hehe.. definitely not!

david_ross · 05-21-2003, 03:29 PM

So on switch one everything is fine.
On switch two - 2 machines can see each other but linux seems invisible.

I assume you have tried linux in a port that you know works from the fact that the other machines worked there.

What about speeds? What speeds are the switches (are they switches and not hubs)? What speeds are the cards?

You can use mii-tool to set the speed of your ethernet card.

dorian33 · 05-21-2003, 03:41 PM

compare the 5th line of the ifconfig output for eth0:
"TX packets:1017 errors:0 dropped:0 overruns:0 carrier:157"
end eth1:
"TX packets:6853185 errors:0 dropped:0 overruns:185 carrier:0"

The 'carrier' <> 0 shows the problems with transmission.
I think the 'overruns'<>0 is also problematic.

Unfortunately these ifconfig output parms are not well documented.
I've looked at source files and it looked like an error counter but it was not worth to study it too much :)

WeNdeL · 05-21-2003, 03:42 PM

Everything is 100 MB...

And all three boxes are linux. We're a RedHat shop.

I am going through every menu in the switch config now. So far nothing has turned up. I will pop back up with more clues if I get them...

*sigh*

I will look at this mii-tool... thanks!

Looking_Lost · 05-21-2003, 04:14 PM

So basically you've got two different isolated network segments:

network card 1 network goes to switch 1
network card 2 network goes to switch 2 ?

I think you've got to bridge the two network cards together somehow, not sure how you to do that on linux yet, XP point and click bridge the two cards. Probably need some IP Tables routing rules,Don't think specifying a gateway on its own will get you anywhere as it'll be a gateway to nowhere - remember switches work with MAC addresses.

Happy to be wrong though