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On computer foo, my ~/.ssh/config has the following entry

Host bar
    User punkish
    Port 2222
    HostName bar.example.org

On computer bar, my ~/.ssh/config has the following entry

Host baz qux
    User punkish
    Port 2200
    HostName %h.example.org

I am able to ssh from foo to bar without any problem ever. Once I am in bar from foo, I am unable to reach anywhere from bar. I can't ping out, I can't ssh, nor curl nor git. Nothing. It is as if there is a firewall blocking me. The image below hopefully explains the problem.

network

Things to note:

  1. I am running Mac OS X 10.8.4 on all machines (foo, bar, baz, qux)
  2. foobar works, but foobaroutside world does not.
  3. Once I am physically at bar, I am able to reach the other machines just fine. That is, baroutside world works fine.
  4. Nothing about the network where bar resides ever changes.
  5. There is no firewall on bar (or, for that matter, on any computer involved in this scenario)
  6. bar has a static IP 10.0.2.20, which is reserved by IANA for private intranets, and not routable to the Internet. bar and is behind a router with the static IP x1.x2.x3.x4. Port 80 and the ssh port on the router are mapped to corresponding ports on bar, so I can reach web sites on bar and can also ssh into bar.

Fwiw

[bar] ~ sudo ipfw list
65535 allow ip from any to any

The command below shows nothing happening on port 2200

[bar] ~$ sudo lsof -i -P | grep -i "listen" 

The most important thing to note — I am able to successfully ssh out when I am physically at bar. It is only when I ssh into bar that I am unable to go anywhere out from bar.

What could be wrong? How do I even begin to investigate this? Is there a command I can use to determine if my ports are blocked, and if so, by what?

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migrated from serverfault.com Jul 28 '13 at 14:06

This question came from our site for professional system and network administrators.

    
And what happens when you try to access the network? –  Michael Hampton Jul 28 '13 at 4:56
    
As mentioned above, I can ssh from foo into bar, but then from bar I am unable to reach anywhere outside. curl, ping, ssh, all of them just hang. No error, no response. I have to CTRL^C to break out. –  punkish Jul 28 '13 at 5:00
    
More information needed. Routing table. Full ifconfig -a output. Show dns servers each host is using. All the configuration details you can show from the 10.0.2.1 device. Then, stop relying on ping for a definitive answer, it causes many unsafe assumptions. Instead, can you telnet to any of these hosts and their appropriate port. For example, when I telnet to one of my hosts on port 22, I at least see "SSH-2.0-OpenSSH_5.3" and you should see something similar from your ports 2200 and 2222. Still more questions, but this should be a good start. –  aharrison Aug 11 '13 at 3:10

1 Answer 1

If bar is FreeBSD (it sounds like from ipfw) then tag this with bsd.

I would first ping the router from bar. Second I would ping and traceroute baz.

But, more importantly, can you reach any server in this scenario? Is the network card / stack broken?

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from #1 in my OP, I am running Mac OS X 10.8.4 on all machines. Yes, I can ping the router at 10.0.2.1 from bar. I cannot ping the router at 64.x.x.x from bar. From #2 and #3 in my OP, if I enter bar via ssh then I can't get out to any machine. However, I can reach anything I want as long as I am physically at bar. That means nothing is wrong with my hardware. A buddy says there might something funky with my routing tables. I don't know how to debug that. –  punkish Jul 30 '13 at 3:47

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