Can't remote login using ssh with DNS

P31 · 02-10-2007, 09:51 AM

I signed up with http://www.no-ip.com/index.php, which provides dynamic DNS services. I have openssh installed and running. On my windows box, I could use putty and ssh in with the 192.168 address. But when I tried it with the hostname, it doesn't work. I have forwarded the port on my router to the ubuntu box and I checked it with http://www.canyouseeme.org/ to see if it's really opened. When I tried to use the hostname instead of ip address, putty would return saying connection timed out. Any idea?

xjlittle · 02-10-2007, 09:59 AM

Did you do this

Quote:

when I tried it with the hostname, it doesn't work

from your internal network? And the hostname that you used is the publicly accessible hostname ie. the one with no-ip?

That won't work unless you are on the internet hitting your port forwarded router. Put a different host name using the internal ip into a hosts file on your machine and it will work.

P31 · 02-10-2007, 10:05 AM

Quote:

Originally Posted by xjlittle

Did you do this

from your internal network? And the hostname that you used is the publicly accessible hostname ie. the one with no-ip?

That won't work unless you are on the internet hitting your port forwarded router. Put a different host name using the internal ip into a hosts file on your machine and it will work.

I see, so if I was to try on the outside, i.e. not in the internal network, then it would work?

xjlittle · 02-10-2007, 10:24 AM

Quote:

I see, so if I was to try on the outside, i.e. not in the internal network, then it would work?

That would be correct. Reason being is when you use the public hostname you leave the internal network via the public ip, go to the internet to resolve and then try and re-enter you internal network via your public ip. Your router\firewall or whatever you have setup won't allow this as it would be seen as spoofing.

P31 · 02-10-2007, 10:26 AM

aah I see. Thanks xjlittle

Hangdog42 · 02-10-2007, 10:58 AM

Quote:

Originally Posted by xjlittle

That would be correct. Reason being is when you use the public hostname you leave the internal network via the public ip, go to the internet to resolve and then try and re-enter you internal network via your public ip. Your router\firewall or whatever you have setup won't allow this as it would be seen as spoofing.

I think this behavior can be router specific. I've got two routers on my network, a Motorolla (for VOIP) and a Linksys (for my general network). If I have my Motorolla router as the WAN facing router (i.e. Internet ->Modem->Motorolla->Linksys->LAN), then I see the same problem as P31. However, if I put my Linksys in Front (Internet->Modem->Linksys->LAN(and Motorolla) then using my no-ip domain from the LAN side works fine.

xjlittle · 02-10-2007, 11:24 AM

Hangdog42 I don't doubt that one bit there are so many routers and configs out there. I went the direction I did because the problem that the OP describes is the one for which I gave that explanation.

Hangdog42 · 02-10-2007, 12:44 PM

Quote:

Originally Posted by xjlittle

Hangdog42 I don't doubt that one bit there are so many routers and configs out there. I went the direction I did because the problem that the OP describes is the one for which I gave that explanation.

Please don't take my post as criticism of your answer. I was just expanding on your explanation a bit.