SSH tunneling error: “channel 1: open failed: administratively prohibited: open failed”

From the SSH Protocol documentation, regarding channels:

All terminal sessions, forwarded connections, etc., are channels. Either side may open a channel. Multiple channels are multiplexed into a single connection.

Channels are identified by numbers at each end. The number referring to a channel may be different on each side. Requests to open a channel contain the sender's channel number. Any other channel related messages contain the recipient's channel number for the channel.

Channels are flow-controlled. No data may be sent to a channel until a message is received to indicate that window space is available.

Port forwarding

The command you have looks fine. Are you sure that the service you're trying to connect to is up and accepting connections? The channel errors would seem to indicate that it's not.

What are my active channels?

If you have an active ssh connection you can use the following key combination to get help:

Shift+~ followed by Shift+?

$ ~?
Supported escape sequences:
  ~.  - terminate connection (and any multiplexed sessions)
  ~B  - send a BREAK to the remote system
  ~C  - open a command line
  ~R  - Request rekey (SSH protocol 2 only)
  ~^Z - suspend ssh
  ~#  - list forwarded connections
  ~&  - background ssh (when waiting for connections to terminate)
  ~?  - this message
  ~~  - send the escape character by typing it twice
(Note that escapes are only recognized immediately after newline.)
debug2: channel 2: written 480 to efd 8

You can then use this key combination to get a list of the active channels:

Shift+~ followed by Shift+#

$ ~#
The following connections are open:
  #2 client-session (t4 r0 i0/0 o0/0 fd 6/7 cc -1)
debug2: channel 2: written 93 to efd 8

It sounds like you're running into the SSH server's limit on the number of simultaneous sessions per connection. Your command-line session to the remote server is one session, and each individual forwarded TCP connection is another session.

You can change the server's limit through the MaxSessions parameter in the server's sshd_config file:

MaxSessions
Specifies the maximum number of open sessions permitted per network connection. The default is 10.

You'd update sshd_config like this:

1. Find the file. It's usually /etc/ssh/sshd_config.
2. Edit it as root.
3. In the file look for an existing MaxSessions setting if any. Otherwise, add a new line. Set the number to 15 or so. Save the new file.
4. Restart sshd to make it reread the file.
5. Make a new ssh connection and see if the behavior changes.