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Azazwa 05-05-2009 05:01 AM
Power-cut. If try pinging, get "connect: Network is unreachable"
 
Hi!

I have a small local network (a half-built cluster), which worked fine (i.e. I could ping and ssh and copy files over the network), until for whatever reason, the room's lights went off for a second, accompanied by the same pitiful results on the computer screen.

I have a normal data switch, and a KVM switch, so that is how I can see what's going on on the nodes.

At present I have the headnode and one of the normal nodes on.
On the headnode:

Code:
[root@gnlserv01 ~]# /etc/init.d/network restart
Shutting down interface eth0:                              [  OK  ]
Shutting down interface eth1:                              [  OK  ]
Shutting down loopback interface:                          [  OK  ]
Disabling IPv4 packet forwarding:  net.ipv4.ip_forward = 0
                                                          [  OK  ]
Bringing up loopback interface:                            [  OK  ]
Bringing up interface eth0:                                [  OK  ]
Bringing up interface eth1: 
Determining IP information for eth1... done.
                                                          [  OK  ]
[root@gnlserv01 ~]# ssh normnode3.up.ac.za
ssh: connect to host normnode3.up.ac.za port 22: No route to host
[root@gnlserv01 ~]# ifconfig
eth0      Link encap:Ethernet  HWaddr 00:1C:C0:AF:10:18 
          inet addr:192.168.1.254  Bcast:192.168.255.255  Mask:255.255.0.0
          inet6 addr: fe80::21c:c0ff:feaf:1018/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:12167 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 b)  TX bytes:784488 (766.1 KiB)
          Base address:0x30c0 Memory:e0300000-e0320000

eth1      Link encap:Ethernet  HWaddr 00:1B:21:2C:70:C2 
          inet addr:137.215.104.218  Bcast:137.215.104.255  Mask:255.255.255.0
          inet6 addr: fe80::21b:21ff:fe2c:70c2/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:30330 errors:0 dropped:0 overruns:0 frame:0
          TX packets:6942 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:100
          RX bytes:6487991 (6.1 MiB)  TX bytes:1279194 (1.2 MiB)
          Base address:0x1000 Memory:e0020000-e0040000

lo        Link encap:Local Loopback 
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:199499 errors:0 dropped:0 overruns:0 frame:0
          TX packets:199499 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:60400966 (57.6 MiB)  TX bytes:60400966 (57.6 MiB)

[root@gnlserv01 ~]# netstat -rn
Kernel IP routing table
Destination    Gateway        Genmask        Flags  MSS Window  irtt Iface
137.215.104.0  0.0.0.0        255.255.255.0  U        0 0          0 eth1
169.254.0.0    0.0.0.0        255.255.0.0    U        0 0          0 eth1
192.168.0.0    0.0.0.0        255.255.0.0    U        0 0          0 eth0
224.0.0.0      0.0.0.0        240.0.0.0      U        0 0          0 eth0
0.0.0.0        137.215.104.1  0.0.0.0        UG        0 0          0 eth1
On the normal node, if I try
Code:
netstat -rn
I just get the headings, but no entries.

Hm, I just don't know enough to put 2 and 2 together. Can someone just enlighten me as how to get 4 please?

:-)

chrism01 05-05-2009 07:32 PM
Well, you need to check the networking on the normnode.
As per above on the server, what does the normnode look like at reboot, /sbin/ifconfig?
Has the NIC died?
Can it see any other system?
Check the network files eg /etc/hosts, /etc/sysconfig/network, /etc/sysconfig/network-scripts/ifcfg-eth0.
Can it ping anything?
Have the firewalls been activated, try turning them off.?

Azazwa 05-06-2009 12:35 AM
Hi!

I feel rather stupid. I rebooted the node and all is fine. I think the problem came because after the power cut, I first booted the normal node, and then the headnode, and the headnode has a DHCP server on it for the local network. I'm not quite clear on why these things happened like it did, but I'll remember to have the headnode operational before the other nodes. I began suspecting this when I powered on the other nodes and they reacted fine.

Oh well, thanks. If something goes wrong with the network again, I'll have a look at those files you mentioned. ;-)


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