[ale] SSH Cisco Networking Issue

Richard Bronosky Richard at Bronosky.com
Sun Sep 26 01:31:42 EDT 2010


So funny reading the responses that followed. When I heard that
cat-ing a large file resulted in NO data as opposed to truncated
data... I was confident that it was something like a packet size
issue. I was not familiar with this MTU thing, but now I'm researching
it out. I love this list. This is why I read it.

On 9/16/10, Omar Chanouha <ofosho at gatech.edu> wrote:
> Hello All,
>
>     Sorry for the long email, but I am having an issue with the IT guy
> at my office, and this problem is out of my league. I set up a
> LAMP/SSH server to host the intranet where I work. I am back at Tech
> now, and need a way to connect to the server (Miami) to make changes.
> I told the IT guy to open a port for me in the firewall so I can get
> to the SSH server. Easy enough right?
>
> So, I can log into the server *.126, and I can send and recieve data
> from it, HOWEVER if I try to receive large (> a paragraph) worth of
> data the client hangs. The firewall still registers a connection, and
> the client will just hang forever(ctrl-c does nothing, I have to close
> the terminal). I would imagine this means it is waiting for data that
> is not going to get there, and is also not receiving a disconnect
> message.
>
> Example:
>
> o at remote:~$cat smallfile
> Hello World!
> o at remote:~$cat bigfile[no response]
>
> the same would apply to listing(ls) a small directory vs a large one.
> Or even TAB completing a long list vs a short one.
>
> At address *.126 there are multiple machines, so when I connect to
> *.126 I get port forwarded to another machine via NAT. Just as a test,
> we made the relationship 1-1 at address *.124 (another ip we own) and
> we made the firewall rule completely open at this address. The server
> then worked. The IT guy then decided to make the rule more strict by
> only allowing connection on port 22, and we went back to the previous
> result. He then put in the Cisco SSH rule (rather than just opening
> port 22) and it worked again.
>
> However, *.124 is not available for full time use, so we went back to
> *.126 and applied the SSH rule, but got the same result as before.
> Here is the weird part, when we port forward *.126 to one of the SSH
> servers on one of the Cisco routers (rather than my machine) SSH works
> fine. The IT guy thinks that the issue is coming from the NAT b/c we
> are using the same firewall rule that worked w/ 1-1.
>
> Question, what could be causing the Ubuntu SSH server to hang ONLY
> when larger amounts of data are being sent, but not affect the Cisco
> SSH servers?
>
> Thanks,
>
> -O
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