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I have 2 machine inside my home LAN (Netgear WNR2000v2 wifi). One of them is a laptop ("client machine") that will always be assigned random IPs in the 192.168.1.1 through 192.168.1.50 range. The other is a desktop ("build server") that I wanted to set up with a "dedicated" IP address; at least from within my LAN.

So I configured the router to always bind the build server's MAC address to a specific IP, namely 192.168.1.52. Apparently, this is called "persistent DHCP reservation."

I am having trouble SSHing from the client machine into the build server. I've noticed that unless the build server has made outgoing TCP requests (to the router) within some small frame of time - about 30 or 60 seconds), the router no longer "sees" the build server, and attempting to SSH into it from the client machine produced No route to host failure messages.

To summarize:

  1. Let the build server go idle/dormant (no network activity for a few minutes).
  2. Open a terminal on the client machine: ssh someUser@192.168.1.52
  3. This produces No route to host errors.
  4. On the build server (an Ubuntu 12.04 deskstop, so not really even a server!), open up a web browser, and go to a few sites (generate network activity)
  5. Back on client machine: ssh someUser@192.168.1.52
  6. Success!

So it's almost as if, after some length of time, a timeout is being reached between the build server and my router, and the router is hanging up. When this happens, and I then try to SSH into the build server, since the router no longer "knows" about it, No route to host.

Also, if I try to ping the build server when it is idle/dormant, the ping fails. If I try to ping the build server when it is not idle (and thus allows me to SSH into it), it pings just fine. Any ideas?

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2 Answers 2

This issue seems like something originating from the router, not the server itself, unless there is a strange set up on the server side. Without knowing what kind of network equipment lies in between the two boxes, it is hard to guess what might be your problem.

As an initial attempt, did you convert from Persistent DHCP reservation (based on MAC) to a static IP configuration ? You can put the same IP address i.e., x.x.x.52 into your build machine as its static address and see if it helps with the timeout issue.

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Instead of fighting with the router that you have on hand, which may change later on, I recommend to tackle the problem from an entirely different angle -- Forget about unreliable/illogical router and its settings, build your own home DNS/DHCP system instead. Forget about addressing your machines with IP addresses, and start using meaningful hostnames instead. That's what I've been doing.

The most comprehensive home DNS/DHCP server setup guide on the net IMHO is,

Providing DHCP and DNS services with DNSMasq
http://sfxpt.wordpress.com/2011/02/06/providing-dhcp-and-dns-services-with-dnsmasq/

So I configure my home DNS/DHCP server once, and it has been happily providing reliable DNS/DHCP service for my home network ever since, even if the server OS has been upgraded several times, and even if several routers have come and go throughout the time.

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