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Old 07-24-2006, 11:52 AM   #1
Registered: Nov 2003
Location: London
Distribution: Debian
Posts: 118

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ping works, nmap and ssh do not

I had ssh working fine for a long time but things have gone wrong today. This is a desktop and a laptop, connected by wireless.

I can access the internet normally from both. I can ssh to the laptop from the desktop but not from the laptop to the desktop. I can ping in both directions. On each computer I can ssh to itself.

nmap in the laptop says that there is no host on the desktop; with the -P0 switch it says "113/tcp closed auth". However, when run on the desktop this command says that various ports are open, including 22/ssh.

I've no idea what has happened here; it doesn't seem to make any sense. Why does ping work although ssh and nmap don't?
Old 07-24-2006, 12:04 PM   #2
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Registered: Oct 2003
Posts: 2,575

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Sounds like a firewall problem on your desktop. Did you change any firewall/ipchains settings on the desktop box? The only other thing I can think of is you may have installed an updated Openssh package on the desktop through some kind of automatic system update service. That can reset all your ssh config files.
Old 07-24-2006, 12:11 PM   #3
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Registered: Oct 2005
Distribution: Gentoo, Slackware, LFS
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i'm not sure but it sounds like a gateway problem. most clients are having difficulty accessing the gateway computer. if your laptop is set as a client and your server as the gateway then you might have a similar problem. try rechecking your config.
Old 07-24-2006, 12:14 PM   #4
Registered: Nov 2003
Location: London
Distribution: Debian
Posts: 118

Original Poster
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Yes, quite right! Turning off shorewall allows the connection. I'm sure I tried that previously without success but it does work now. I havent changed shorewall recently so I shall have to research this further.
Old 07-24-2006, 12:15 PM   #5
Registered: Jun 2005
Location: Chicago, IL, USA
Distribution: Fedora Core, CentOS
Posts: 188

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Assuming you can disconnect from the internet the router that these computers are connected to, disable the firewalls on both machines.

1) login as root in the command prompt
su -
2) disable the firewall
whatever the firewall is in debian stop it.

Now try the SSH for both of these machines. If that can work you can say that it is a firewall issue.

Process of elimination:
physical, both are connected to the AP
data link and networking, ping and internet work
transport, ports may not be opened to receive data (firewalla issue)
Old 07-24-2006, 02:27 PM   #6
Registered: Nov 2003
Location: London
Distribution: Debian
Posts: 118

Original Poster
Rep: Reputation: 16
Thanks again to everyone. I found the problem in the end: there was an entry in /etc/shorewall/rules to allow the IP of my card, but the IP had changed.


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