setsockopt IPV6_TCLASS 16: Protocol not available, Cygwin64

Question

I'm trying to install Hadoop 1.0.3 using Cygwin64 on Win8.1. After I completed the config, started SSHD service, I run ssh cyg_server@localhost and got these:

cyg_server@localhost's password:
setsockopt IPV6_TCLASS 16: Protocol not available:

I'm complete new with Cygwin64 and Hadoop, thanks advance for any help.

Answer 1

From the client side, just add

-oAddressFamily=inet

to the parameters passed to ssh, or add

AddressFamily inet

to ~/.ssh/config, either globally or per a specific host.

Answer 2

Basically you want to turn off IPV6 and use IPV4. To do this, stop your sshd service if you have it running:

net stop sshd

Then edit the file /etc/ssh_config by adding (or modifying) the AddressFamily setting:

AddressFamily inet

The default is set to all. Setting the value to inet forces IPV4 which fixed the problem for me. After you make the change, restart sshd and you should be good to go:

net start sshd

Good luck!

Answer 3

I had a simmilar issue with Cygwin logging in to IPv6-enabled Servers.

Upgrading Cygwin (on client side) to the lastest version solved my problem.

I'm tired of all the "Just disable IPv6" suggestions. We have 2014 and IPv6 is here. We should better fix bugs and issues with this "new" protocol instead of negating ist.

Answer 4

This error happens when OpenSSH attempts to set the "type of service" field for an IPv6 connection on a system that defines IPV6_TCLASS in <sys/socket.h>, but where the kernel doesn't support it (a 2.4-series kernel or older versions of Cygwin).

It may reduce performance in a situation where something is performing traffic shaping/QoS, but is otherwise harmless.

Answer 5

If you see such issue on WSL1/OpenSSH client and you need to use IPv6 protocol then try to use ssh -oIPQoS=none ... or add IPQoS none to your ~/.ssh/config or systemwide SSH config.

As Mark mentioned here it may be due to unsuccessful attempt to set "type of service" for IPv6 connection.