PuTTY bug portfwd-addr-family

summary: Unix listening sockets (e.g., tunnels) are IPv6-only by default
class: bug: This is clearly an actual problem we want fixed.
difficulty: fun: Just needs tuits, and not many of them.
priority: high: This should be fixed in the next release.
present-in: 0.60
fixed-in: r8150 2008-08-21 (0.61) (0.62)

On a Unix system supporting IPv6, PuTTY will by default create listening sockets (e.g. for the local end of a local-to-remote tunnel) as IPv6-only. Attempts to connect to the port using IPv4 addresses (127.0.0.1) will fail, and often the same problem will occur with the name "localhost". This occurs for instance on Ubuntu Linux (so this is probably what's behind LP #67488).

This contradicts the documentation of the default "Auto" setting for tunnels, which states that "ticking 'Auto' should always give you a port which you can connect to using either protocol."

Unix PuTTY should ensure that listening sockets are valid for at least the address families specified in the configuration.

Workarounds:

Explicitly configure PuTTY to use an IPv4 listening socket (change 'Auto' to 'IPv4'). Of course, you won't then be able to connect to the tunnel endpoint with IPv6; if you need to be able to connect with both protocols, set up two tunnels with the same destination.
Leave the PuTTY configuration as it is, but explicitly connect to the IPv6 localhost address (::1).

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(last revision of this bug record was at 2008-08-20 23:21:04 +0100)