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I am trying to connect to an external host that is living in the Internet.

From my laptop I can ssh fine. From an Ubuntu 12.10 server, the connection times out.

Since they're in the same network, they are originating from the same IP address.

The server receives the initial packets from the server but never acknowledges them (after looking at a tcpdump).

I'm having a hard time figuring this one out. Nothing in iptables, nothing in hosts.allow/deny...

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You mean the server is not answering to the TCP SYN? I would tcpdump both the TCP SYN from the laptop and the ubuntu machine and compare them in wireshark/tshark -V – Stephane Chazelas Nov 15 '12 at 23:04
ssh -v to see where it is hanging. Use -vv or -vvv to get more detailed log. – peterph Nov 17 '12 at 21:41
@StephaneChazelas that is correct, doing a tcpdump from both, and an ssh -v the laptop initiates the connection and never receives a tcp syn. It's like the system is using tcpwrappers, but it's not... – Specto Nov 20 '12 at 14:50
Can you add the tcpdump output for both laptop and the ubuntu? – ott-- Dec 16 '12 at 1:11

2 Answers

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If iptables is active (i.e. the Linux firewall), then it might be configured not to allow this.

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The OP indicated that they had looked through iptables... – jasonwryan Nov 16 '12 at 1:12
iptables isn't configured to drop ICMP answers by default (as the "times out" seems to indicate). Very weird. --- Please do double-check on iptables configurations of both machines. Or perhaps the server is connected via Ethernet to the wireless router, and the notebook via WiFi, and the router has different rules for them? Can you connect from the server to the notebook via ssh? Viceversa? – vonbrand Jan 24 at 17:53
up vote 0 down vote

ssh -vvv is going to give you all of the information you'll need and will help everyone determine what the root cause is.

You can try recreating your keys and sending them to the server. Create a key if you don't have one. If you do then use step 2.:

1. ssh-keygen -t rsa (use defaults)
2. ssh-copy-id -i ~/.ssh/id_rsa.pub $USER@$FQDN

You could also try ssh -T or maybe your windows box has different info in it's host file. So, try connecting to the server via it's IP address.

Sorry, but without knowing what ssh -vvv is there isn't much more I can suggest.

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