Score:2

Domain only reachable over browser as long as ping is running *on the server* (also ssh doesn't work)

ph flag

I have a remote machine on which I run Debian and Apache. Recently, a strange problem occured.

It started with me not being able to log in by ssh anymore (I simply get a timeout) and my domain not being reachable over the browser. I think I couldn't ping it as well but I'm not sure about this. As of now, ping works.

Using the control panel of the provider, I am still able to log in. ip link shows that the interface is UP. The strange thing is that while I run ping google.de on the server, the domain suddenly is reachable from the browser. After aborting the ping, the domain stops being reachable again. SSH works in none of the cases.

My first goal is to understand this strange behaviour, my second goal is to get SSH (and my domain) back to work.

digijay avatar
mx flag
That sounds much like a connectivity problem on the side of your provider, ask him if there is something down (e.g. a router or switch), most providers will have status sites aswell. To test the http connection instead of a browser rather use `curl -I https://yourdomain.example.com/` because it won't give you any cached results.
cssdev avatar
ph flag
@digijay: Thanks for the tip!
Score:4
in flag

This could be a duplicate ip-address issue. Some other host in the subnet has snatched your ip-address. Ping works because it is stateless, and whatever host gets the ping request, will send the ping reply.

Then, when you ping google from your server, your host will claim the ip-address, and the provider's routers/firewalls will update their arp-table.

If you check the /var/log/syslog file it should report that some other host is using your ip, and you should also be able to see the other host's mac address. If you find this info, you need to contact your provider to rectify the issue.

cssdev avatar
ph flag
Thank you, this is likely the explanation. I'll contact my provider about this the next workday where I can access my server. I guess I don't absolutely need the other host's mac address but I am interested in how I could get it from the syslog. I tried grepping for "mac", "ip", etc but didn't find anything. Could you guide me here?
cn flag
You can not. The MAC Address is only "relevant" in regards to an Ethernet broadcase segment. It should be in the switch logs or accessible through the switch, but not from your side.
Sven avatar
in flag
Sorry, my memory served me wrong.. You may not be able to detect the duplicate ip in /var/log/syslog. However, you may be able to detect the other host if you install arping on your server: http://kb.eclipseinc.com/kb/how-do-i-check-for-duplicate-ip-addresses-in-linux/
cssdev avatar
ph flag
Just FYI @Sven (sorry for commenting so late) and others having the same problem: it indeed was a problem with my hosting provider. The employee didn't think it was the issue described here and solved it by moving my VPS to a different physical machine. Which seems like essentially vodoo to me :-)
mangohost

Post an answer

Most people don’t grasp that asking a lot of questions unlocks learning and improves interpersonal bonding. In Alison’s studies, for example, though people could accurately recall how many questions had been asked in their conversations, they didn’t intuit the link between questions and liking. Across four studies, in which participants were engaged in conversations themselves or read transcripts of others’ conversations, people tended not to realize that question asking would influence—or had influenced—the level of amity between the conversationalists.