Comment 9 for bug 707705

I did some more testing on this problem, and it seems that even changing the port will not work with a network_interface specified. E.g. without network_interface set, and alternate_port set to 5995, I can connect to the server via 'vncviewer <target>:5995'.

After setting the network_interface to lo and using ssh tunneling, the connection attempt fails:

vncviewer -via ubuntu@<target> <target>:5995
ubuntu@<target>'s password:
channel 3: open failed: connect failed: Connection refused
vncviewer: VNC server closed connection

However, on <target> there is definitely a process listening on 5995:

tcp 0 0 127.0.0.1:5995 0.0.0.0:* LISTEN 1115/vino-server
tcp6 0 0 ::1:5995 :::* LISTEN 1115/vino-server

As an experiment, I connected to <target> via ssh -Y for X forwarding, and run vncviewer, which worked:

$ vncviewer localhost:5995
Connected to RFB server, using protocol version 3.7
No authentication needed
Desktop name "ubuntu@lucid"
VNC server default format:
  24 bits per pixel.
  Least significant byte first in each pixel.
  True colour: max red 255 green 255 blue 255, shift red 16 green 8 blue 0
Using default colormap which is TrueColor. Pixel format:
  32 bits per pixel.
  Least significant byte first in each pixel.
  True colour: max red 255 green 255 blue 255, shift red 16 green 8 blue 0
Same machine: preferring raw encoding

I then tried to use port forwarding with ssh, 'ssh -L 5995:<target>:5995 ubuntu@<target>', but this failed with:

$ vncviewer localhost:5995
vncviewer: VNC server closed connection

With that being unsuccessful, I tried a ssh/ppp tunnel, as a sort of VPN replacement:

$ sudo /usr/sbin/pppd updetach noauth silent nodeflate pty "/usr/bin/ssh root@<target> /usr/sbin/pppd nodetach notty noauth" ipparam vpn 10.0.0.1:10.0.0.254

Note that the root user needs to be enabled on <target> for the above to work. I could not figure out how to use sudo on <target> to get a pppd running. With this crutch, I could connect to both vino servers at different ports:
vncviewer 10.0.0.254:5995
vncviewer 10.0.0.254:5999

However, I could not get it running without the alternate_port specification.