I can't connect via ssh

[Germán Racca]

On Sat, 2009-09-26 at 15:30 -0400, Erik Hemdal wrote:
> 
> > From: Germ?n Racca <german.racca at gmail.com>
> > Subject: Re: I can't connect via ssh
> > To: "Community assistance, encouragement, and advice for using
> > Fedora." <fedora-list at redhat.com>
> > Message-ID: <1253925734.7784.27.camel at centauri.das.inpe.br>
> > Content-Type: text/plain; charset="UTF-8"
> >
> > On Fri, 2009-09-25 at 18:32 -0500, Aaron Konstam wrote:
> >> On Fri, 2009-09-25 at 16:20 -0300, Germán Racca wrote:
> >> > Hi list:
> >> >
> >> > I need to use ssh to transfer data between a PC and a notebook, both
> >> > with Fedora 11, but the result is, from notebook to PC:
> >> >
> >> >
> >> > $ ssh xx.xx.xx.xx
> >> > ssh: connect to host xx.xx.xx.xx port 22: No route to host
> 
> It might help to picture what has to happen for an SSH connection to work:
> 
> --You have to make a request with the ssh command on the client machine, 
> where you are sitting.  If you can craft an ssh command, as you did, this is 
> probably not your problem.
> --The SSH traffic has to get past the local firewall.  By default, this 
> isn't usually a problem, because the firewall will allow outbound traffic. 
> If you can browse the Web and get email, this is probably OK and is not the 
> source of your problem.
> --The SSH traffic has to get through your network.  It might be blocked 
> because your network administrator forbids SSH or because there's some other 
> problem.  So we need to investigate this first.
> --The firewall on the remote computer (the one you want to "SSH into") has 
> to let the SSH traffic in.  This is usually done by telling the firewall to 
> "trust SSH" or "open port 22".
> --The remote computer has to have an SSH server running and ready to go. 
> This is the "service sshd start" part.
> 
> The error "No route to host" means that your SSH packets could not find 
> their way to the computer at xx.xx.xx.xx.  That might be because the 
> firewall on that computer hasn't opened port 22 (common) or because the 
> computer can't be reached through the network.
> 
> Pinging the computer uses a different kind of message ("ICMP packets") to 
> see if the computer can be contacted.  But you don't want to ping localhost, 
> because that is pinging your local PC.  So it will tell you if the network 
> interfaces on the two computers are working, but won't tell you if they are 
> visible to each other on the network.  On my laptop, "ping localhost" works 
> even when my network connections are disconnected from everything.
> 
> To make sure, you need the IP addresses; any computer at all should respond 
> when you call it localhost.  Ping from one computer using the IP address of 
> the other one.
> 
> ping xx.xx.xx.xx
> 
> with the actual IP addresses will tell you a lot.  If the pings are 
> successful, then you know that there is a connection between the two. If 
> not, you need help from your network administrators to know if the 
> connection is possible.
> 
> The ifconfig command will tell you the IP address (inet address) for each 
> network interface that is up.
> 
> >> >
> >> > $ ping xx.xx.xx.xx
> >> > >From xx.xx.xx.xx icmp_seq=11 Destination Host Unreachable
> >> > >From xx.xx.xx.xx icmp_seq=12 Destination Host Unreachable
> >> > >From xx.xx.xx.xx icmp_seq=13 Destination Host Unreachable
> 
> Destination Host Unreachable means that the remote computer can't be found. 
> There's no way to get an ICMP packet to reach it.
> >> >
> >> > >From PC to notebook there is no response.
> 
> This is what I'd expect if the computer can be found on the network, but it 
> is deliberately not responding to pings -- or if something like a firewall 
> is in the way and blocking pings.  In either case, this looks like a network 
> issue.  There may be other problems too, but making sure the network is OK 
> is first on the list to solve.
> 
> Post back if you need more help.  I hope this will help you.  These kinds of 
> problems can be very hard to solve.
> 
> Erik 

Hi Erik,

Thanks for your clarifying message! Now I discovered the following:

I can ping and connect via ssh from other computer to my notebook, but
*I can't from other computer to my PC*. The messages, from other
computer to my PC are:

$ ssh xx.xx.xx.xx
ssh: connect to host xx.xx.xx.xx port 22: No route to host

$ ping xx.xx.xx.xx
>From xx.xx.xx.xx icmp_seq=11 Destination Host Unreachable

I'm going to contact the network administrator on Monday, but I hope
that you and the other guys that answered to my post can continue to
help me on this issue. Sorry for my bad English ;-)

Germán.
-- 
Germán A. Racca
National Institute for Space Research (INPE)
São José dos Campos - SP - Brasil
http://gracca.wordpress.com
http://tinyurl.com/SkyTux