Opened 6 years ago

Last modified 5 years ago

#1235 infoneeded bug

channel XXX: open failed: unknown channel type:

Reported by: diaz8@… Owned by:
Priority: normal Milestone:
Component: unknown Version: rc2
Severity: unknown
Cc: Hardware: 2.0n (FON2300)



This problem only occurs when using Fonera as a Proxy through SSH. Browsing starts to slow down and finally fails to get web pages.

I have RC2 installed with Tinyproxy 1.8.2 built by myself. I have also tried with beta 3 and RC1 and Tinyproxy 1.6.4 from

The problem arises after using the configuration explained above: Connecting LaFonera? through SSH and using Tinyproxy as a proxy.

After browsing a little (few minutes) at the console of SSH begins to show multiple messages: channel XXX: open failed: unknown channel type:

If i restart tinyproxy things starts to run again, but after few minutes it returns.

I have been using LaFonera? with this scenario long time ago. There have been any changes in my Fonera configuration, only the location from I connect to SSH.

Accessing internet from this location without proxy don't show any problem. There is no problem also when using internet connected at home directly to LaFonera?.

My OS is Ubuntu 12.10. Firefox 17.0 and Firefox Nightly 20.0.

I don't know the way of debugging the problem, could you tell me some steps to try to search where the problem is?.


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Change History (3)

comment:1 Changed 6 years ago by matthijs

  • Status changed from new to infoneeded

Just to confirm I understand your setup:

  • Tinyproxy is running on the Fonera. This is a normal HTTP proxy that listens on a local TCP port (e.g., localhost:8080 or something).
  • You set up an SSH connection to the Fonera with SSH port forwarding (e.g., localhost:8080 on the Ubuntu machine is forwarded to localhost:8080 on the Fonera).
  • You set up a HTTP proxy in your browser to point to the forwarded local port (e.g., localhost:8080).

Am I understanding correctly?

I had a look at where the error message comes from. It is generated by your OpenSSH client running on Ubuntu, but the failure is triggered by dropbear (the SSH server) on your Fonera.

Looking at the dropbear source code (recv_msg_channel_open in common-channel.c), it seems to return the SSH_OPEN_UNKNOWN_CHANNEL_TYPE for different kinds of errors. The fact that it works initially suggests that the channel type isn't really unknown, so it seems likely that no more free channels are available, causing newchannel to fail.

I thought that perhaps dropbear wasn't cleaning up used channels properly, but I just tested a port forward with opening and closing one connection each second and it is still working after 600 connections.

If I instead open and close connections as fast as possible, I do get the error you describe (however, all of the actual connections seem to succeed, netcat isn't showing me any errors, but perhaps the connection would break if I actually sent some data through it).

Perhaps your browser is not properly closing down TCP connections, causing a lot of them to remain open in parallel? Or perhaps it is using too many connections in parallel? Dropbear should support around 100 simultaneous forwarded connections.

Perhaps running "netstat -t -n" on your Fonera helps to see if there are in fact a lot of open connections (connections in TIME_WAIT state shouldn't hurt, AFAICS).

Did you ever try waiting for some time instead of restarting tinyproxy? Does the problem perhaps go away by itself after a few minutes?

You say restarting tinyproxy helps, but do you also re-establish the SSH connection? Or is just restarting tinyproxy enough (in which case the above analysis might not be applicable...)?

comment:2 Changed 5 years ago by Travon

So true. Honesty and everything regencizod.

comment:3 Changed 5 years ago by Ramil

Who Cares,I would like to try to use Dropbear on my surplus Duo. I have <a href="">instllaed</a> the programme but not sure what to do next. I have played with rsync over ssh between a NVX and a Pro and would have thought it was a similar process. Are there any very short instructions.

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