Hi,
I've installed a mail server using CentOS 4.4
Now, if i reboot the server remotely by ssh, when it cames up, i have no network. The interface is up and everything looks pretty fine. But i can't even ping other machines in the same intranet.
If i reboot it locally at the console, the network cames just fine.
Never seen nothing like this.
The mind boggles :(
Any ideas ?
Warm Regards, Mário Gamito
-----Original Message----- From: centos-bounces@centos.org [mailto:centos-bounces@centos.org] On Behalf Of Mário Gamito Sent: Saturday, March 03, 2007 4:33 PM To: CentOS mailing list Subject: [CentOS] The most weird thing i've ever seen (networking)
Hi,
I've installed a mail server using CentOS 4.4
Now, if i reboot the server remotely by ssh, when it cames up, i have no network. The interface is up and everything looks pretty fine. But i can't even ping other machines in the same intranet.
If i reboot it locally at the console, the network cames just fine.
Never seen nothing like this.
The mind boggles :(
Any ideas ?
Warm Regards, Mário Gamito
Any log entries?
-----Original Message----- From: centos-bounces@centos.org [mailto:centos-bounces@centos.org] On Behalf Of Mário Gamito Sent: Saturday, March 03, 2007 5:33 PM To: CentOS mailing list Subject: [CentOS] The most weird thing i've ever seen (networking)
Hi,
I've installed a mail server using CentOS 4.4
Now, if i reboot the server remotely by ssh, when it cames up, i have no network. The interface is up and everything looks pretty fine. But i can't even ping other machines in the same intranet.
If i reboot it locally at the console, the network cames just fine.
Never seen nothing like this.
The mind boggles :(
Any ideas ?
How do you attempt to ping the other machines after you reboot via ssh, at the console?
Is it possible that a piece of network equipment is proxying the arp when you reboot via the network and will not let go once the machine comes back up, but when you reboot locally there is no network connection that would need arp proxying so a proxy entry isn't created?
You would have had to turn on arp proxying somewhere for this to happen though it doesn't happen automatically.
Need to know your network topology a bit more to fully diagnose this.
-Ross
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If you use DHCP and are connected to a cisco switch, sometimes the link won't come up (if you are using the default settings).
This may not be your specific problem but in general I recommend that you don't use DHCP on servers for this reason.
John.
Mário Gamito wrote:
Hi,
I've installed a mail server using CentOS 4.4
Now, if i reboot the server remotely by ssh, when it cames up, i have no network. The interface is up and everything looks pretty fine. But i can't even ping other machines in the same intranet.
If i reboot it locally at the console, the network cames just fine.
Never seen nothing like this.
The mind boggles :(
Any ideas ?
Warm Regards, Mário Gamito _______________________________________________ CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos
--- John Newbigin jnewbigin@ict.swin.edu.au wrote:
If you use DHCP and are connected to a cisco switch, sometimes the link won't come up (if you are using the default settings).
(snip)
But i can't even ping other machines in the same intranet.
John, he said he can't even ping! What have a Cisco switch and the DHCP to do with an interface not coming up at all?!
If i reboot it locally at the console, the network cames just fine.
Now, is there any difference between a local reboot and a remote one?!?!
The mind boggles :(
Mine too (it's 3 AM here).
R-C
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On Mar 4, 2007, at 7:01 PM, Radu-Cristian FOTESCU wrote:
What have a Cisco switch and the DHCP to do with an interface not coming up at all?!
Some Cisco switches take a long time to negotiate link speed, duplex, and bridge forwarding when left at default settings. This causes the initial DHCP requests to time out, leaving you with no IP address as the box comes up. dhclient should finally run again and get an address, but it can take a few minutes.
You can speed this up by using the "portfast" keyword, but do be careful and read up on it before enabling it. Portfast on the wrong port can cause a network meltdown.
--Chris
Chris Boyd wrote:
On Mar 4, 2007, at 7:01 PM, Radu-Cristian FOTESCU wrote:
What have a Cisco switch and the DHCP to do with an interface not coming up at all?!
Some Cisco switches take a long time to negotiate link speed, duplex, and bridge forwarding when left at default settings. This causes the initial DHCP requests to time out, leaving you with no IP address as the box comes up. dhclient should finally run again and get an address, but it can take a few minutes.
You can speed this up by using the "portfast" keyword, but do be careful and read up on it before enabling it. Portfast on the wrong port can cause a network meltdown.
--Chris
For those who want to understand the portfast concept:
http://www.cisco.com/warp/public/473/65.html
In resumé, Cisco switches run STA (Spanning Tree Algorithm) on all ports by default to avoid networking loops that can take the network down.
Portfast is a parameter that immediately transitions the blocked port in forwarding state upon link up instead of transitioning the port after STP Calculation that can take between 30 and 50 seconds. Ports in Portfast mode still participate in STP.
Portfast is used for ports that connect hosts.
Guy Boisvert, ing. IngTegration inc.
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Chris Boyd -
Guy Boisvert -
John Newbigin -
Mike Kercher -
Mário Gamito -
Radu-Cristian FOTESCU -
Ross S. W. Walker