Hi,

This problem has been occurring a lot lately.

If I use an IPMI or KVM device and log into the server I can ping 8.8.8.8, or any website for that matter. However, when I try to ping the public IP address of the server it's non responsive at 100% packet loss. SSH doesn't work either.

First thought: Firewall . So I disable the firewall. --> Still cant ping or access server.
Second thought : Maybe I missed something with the firewall - so i co0mplertly remove it. I'm still unable to ping or access the server but the server can still ping google and so on.

The Operating system used is Centos 6/64 bit.

Please tell me someone can help!

Run tcpdump -i eth0 icmp (and replace eth0 with the correct interface) to see if anything arrives at the interface. If not, you should consider a problem with the network setup outside of the server.

What's the output of:

I cant really copy and paste from the KVM so I'll have to attach an image of the KVM screen.

This one shows route -n and ifconfig lo

Attached Thumbnails

 

Attached is the tcpdump command you requested.

Still not resolved.

Attached Thumbnails

 

If I reformat this server and re setup everything it will work again but then after a few months the same thing happens. It pings out but I cant reach it via SSH or any other method.

Abny suggestions and help is greatly appreciated.

Hi Jeffneils, I had the same issue in the past but it wasn't a configuration problem it was my ISP that was blocking the ping from within my network to the same network.
Did you try to ping the server from the outside? You can try this using your mobile phone if it's not connected to your net via wirelesss.

I did, i tried from multiple different networks and multiple iPs. Still the same.

Hi, can you post the output of ifconfig (without lo at the end). Also, what happens if you run iptables -L

Thanks

Neil

I can see that Berndbausch has the right idea. Run tcpdump and then using another device ping your server. Look to see if anything is registered. I would suggest however that you redirect the output of tcpdump to a text file. It's just much easier to scroll through and high light, cut/paste what you receive. You do not have to record an ICMP response. The line below will capture literally everything generating traffic from and to your server.

# tcpdump -i <interface> > testFile

If you do not record anything from your outside pings, then what kind of networking equipment or firewalls are between you and the Internet? Those you will need to investigate.

If this system's firewall or routing table were at the root of the problem, you would at least see the packets arrive at the interface and perhaps get ignored or actively refused. However nothing arrives.

Either the interface is somewhat misconfigured at the hardware level or, more likely IMO, something outside that server blocks it. Talk to the network team.

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Let me guess---
your server talks to a router which talks to the gizmo that handles conversations with the outside world?

Login to your server; from there enter your ROUTER and make sure it is ping enabled and then try again.
if you want the ISP assigned address, look in your router's "config" tables.
probably called WAN ADDRESS or some such.

If you are hoping to be able to create your own address updater - you may need to put aside some time for doing this.

Norseman01