[CentOS] strange network problem

Michael Schumacher michael.schumacher at pamas.de
Fri Mar 5 13:00:41 UTC 2010

Nobody having an idea?

> Hi,
> I am trying to fix a problem I have for about a week now.
> The environment is:
> --several independent servers with Centos5.4 on the latest patchlevel
> (example will be server2) All of them are working properly.
> --a machine with Xen installed to host some virtual machines
> (xenserver1)
> --domu servers on xenserver1 (crmserver1, winserver1)

> The whole network is connected with a Lancom router to a DSL line.

> Some days ago I noticed that server2 was updated properly, but
> xenserver1, crmserver1 and winserver were not updating the OS
> properly. They seemed to be cut off the internet. I can ping from all
> to all servers internally, I can ssh from all to  all servers
> internally and I can browse the Internet from server2 successfully
> (using IP-numbers and hostnames), but xenserver1 and its domu clients
> could not connect to the internet. I checked the firewalls on
> xenserver, and crmserver1. They seemed to be OK and stopping them with
> "etc/init.d/iptables stop" didn't solve the problem.

> I can resolve hostnames:

>>[root at xenserver1 ~]# nslookup www.centos.org
>>Non-authoritative answer:
>>Name:   www.centos.org

> but I cannot browse neither to "elinks http://www.centos.org" nor to
>, however, I can ping www.centos.org successfully.

> the network routes seem to be OK :

>>[root at xenserver1 ~]# route
>>Kernel IP routing table
>>Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
>>        *        U     0      0        0 eth1
>>   *        U     0      0        0 virbr0
>>     *          U     0      0        0 eth0
>>     *          U     0      0        0 eth0
>>default         LANCOM_1751_1.p         UG    0      0        0 eth0

> (eth1 is a drbd interface)

>> [root at crmserver1 ~]# route
>> Kernel IP routing table
>> Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
>>     *          U     0      0        0 eth0
>>     *          U     0      0        0 eth0
>> default         LANCOM_1751_1.p         UG    0      0        0 eth0

> Has anybody any clue where to look?

best regards
Michael Schumacher

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