Problem solved! ChatGPT skirted around the solution, and should have
asked for the output of ifconfig on both computers - that would have
saved me a lot of time.
Anyway, here's what my diagnosing led me to:
The server can ping the client.
The client can ping the server.
The server can ssh to the client.
Another computer can ssh to either client or server.
When the client tries to ssh in to the server, the server sees the SYN
and acknowledges it, but the client never sees it.
Cause: netmask on the SERVER was wrong, resulting in the server trying
to use the firewall as a router. Ping worked in this case, but ssh
wouldn't. (netmask on server was 255.255.255.0, the correct mask is
255.255.252.0).
This was the result of my entering the netmask as a bit count, not as a
bit field, and I was off by 2 bits.
Fixed, now all works!
On 7/9/24 17:19, Rusty Carruth via PLUG-discuss wrote:
> I wish my answer was that simple! Ok, I'm off to try chatgpt... Wow,
> I'm impressed... It hasn't help me find the issue, other than the
> interesting fact that the file server is responding to the SYN request
> just fine, but the laptop isn't seeing it! (wireshark on both sides -
> is your friend!)
>
> All sorts of nice ideas. It does get a bit stuck on some ideas, and
> repeats them even after I've tried to tell it that isn't applicable.
> Oh, well. I'm now going to try rebooting the laptop and see if that
> fixes it....
>
>
> On 7/9/24 15:51, Keith Smith via PLUG-discuss wrote:
>> By using ChatGPT I was able to determine SSH was not installed on my
>> desktop. I did the install and now it works.
>>
>>
>>
>> On 2024-07-09 15:30, Keith Smith via PLUG-discuss wrote:
>>> Rusty,
>>>
>>> I was unable to SSH into my desktop from a new Ubuntu VirtualBox
>>> guest this morning. Was able to ping. Have not had the time to
>>> resolve.
>>>
>>> My response is to your mentioning AI. I use the free version of
>>> ChatGPT. It is version 3.5 It responds to normal language. Ask it
>>> a question like you would ask me. Then refine your question based on
>>> what it's response is.
>>>
>>> I just went to https://chatgpt.com/ and did not sign in and asked
>>> "Why do I get an error when trying to SSH into my kubuntu desktop
>>> from a ubuntu 24.04 server running on VirtualBox. I an ping."
>>> Notice I misspelled can at the very end.
>>>
>>> These questions are called prompts. And are regular English.
>>>
>>> I got a ton of information... And I can continue to refine my
>>> question. In this case it looks like this is all I might need.
>>>
>>> I created a YouTube video on using AI to create PHP programs :
>>> https://youtu.be/k7CNqcKxKTg
>>>
>>> Keith
>>>
>>>
>>>
>>>
>>>
>>>
>>> On 2024-07-09 15:07, Rusty Carruth via PLUG-discuss wrote:
>>>> Hopefully the answer isn't that *I'm* the insane one! ;-)
>>>>
>>>> So, my laptop, which is running Linux Mint 20.2 Uma, and my file
>>>> server have suddenly had a falling-out. They used to talk to each
>>>> other just fine, but now the file server, running Linux Mint 19.3
>>>> Tricia, slams my laptop into the deny list as soon as I try to SSH
>>>> in to it. And I don't (believe I have) automatic update enabled on
>>>> either computer, and I certainly don't remember doing anything to
>>>> the laptop or the server related to networking. The laptop has an
>>>> NFS connection to the file server - or it HAD before the blocking!
>>>>
>>>>
>>>> The file server has no problem ssh-ing to the laptop (no surprise
>>>> there, of course).
>>>>
>>>>
>>>> Initially I thought it was some problem with port 161, but I added
>>>> that (and the laptop IP address!) in to the portsenty ignore file,
>>>> and it still got flagged.
>>>>
>>>>
>>>> It isn't in hosts.deny, nor is it in the portsentry bad guys list.
>>>>
>>>>
>>>> I looked (find /etc -type f -print0|xargs -0 egrep <laptopIPaddr>')
>>>> on the file server:
>>>>
>>>> Tue Jul 09 14:02:30 RustyC ~ $ cat /tmp/finding.laptop
>>>> /etc/portsentry/portsentry.ignore.static:myLaptopIP
>>>> /etc/portsentry/portsentry.ignore:myLaptopIP
>>>> /etc/portsentry/portsentry.ignore.static~:myLaptopIP
>>>> Tue Jul 09 14:05:59 RustyC ~ $
>>>>
>>>> (I hacked the local IP to the string 'myLaptopIP'. What is
>>>> actually there is the actual IP addr).
>>>>
>>>>
>>>> So, I removed (uninstalled) portsentry from the file server,
>>>> rebooted, and tried again. Still blocked! Waited about a day,
>>>> still blocked. So, I changed the IP address of the laptop - the
>>>> server blocks the laptop!
>>>>
>>>> Just for fun, I changed my laptop's IP again and tried mounting the
>>>> file server via NFS, without doing anything else (no attempt to
>>>> ssh, etc) - blocked, as far as I can tell. BUT! I can still ping
>>>> the file server from the laptop!
>>>>
>>>> Checked iptables - NOTHING in any table on the server. I'm totally
>>>> stumped, and about to re-install Linux on both the Laptop and the
>>>> file server. (One of these days I hope to get time to fool with AI
>>>> for this kind of thing, but haven't yet had the time...)
>>>>
>>>> Does anyone have any ideas? Thanks!
>>>>
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