SSH not working to C3 compute-optimized machines

Question

I cannot connect to any machine I create on EC2 that belongs to the C3 family.

I have no problem connecting with SSH to any other type of machine.

What do I need to do to further debug this?

The steps I've taken:

• I create a t1.micro machine with the same image (an ubuntu 13.10 64bit AMI ami-2f252646), and the same key-pair, and hte same security group. It works fine.
• I ssh to a t1.micro machine, and then ssh again from that machine to the C3 machine. That tells me the machine is up and running and my problem is connecting to the C3 machine from my PC directly (going through the office router).
• I try to telnet to the t1.micro machine on port 22 - I get a connection.
• I try to telnet to the C3 machine on port 22 - does not work.
• I try to telnet to the C3 machine on port 22 from another PC, not from the office - I get a connection.
• I tried this with several C3 type machines, all iwht the same result.

So:

• The machine is up and running, and can accept connections.
• There is obviously a problem in the coupling between my office connection and the C3 machine.
• My office connection works fine with any other type of m1/c1/g1/m2 machine, so it's only the "3" family that has that problem.

I'm at a loss on how to solve this, or even debug this further. Right now I'm tunneling to my machine through a proxy t1.micro machine...

My operating system is itself Ubuntu 13.10

Here is a gist link to the output of my ssh -vvv command

It seems to get stuck at debug1: expecting SSH2_MSG_KEX_ECDH_REPLY

Answer 1

Solved it, with the help of AWS professional (paid) services.

The problem is with some of the authentication protocols. I have a high (9000) MTU (minimal transfer unit) configured in my network connection, I need this to access big chunks of data.

The solution is either to lower the MTU to below 1400 (which is not good for me, because I need it), or to change the SSH config, which worked for me.

sudo vi /etc/ssh/ssh_config

and uncomment the lines starting with Ciphers and MACs

mine says:

Ciphers aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc
MACs hmac-md5,hmac-sha1,[email protected],hmac-ripemd160

This is a bug from Ubuntu 12.10 and onwards (it works in 12.04 and below)