SSH_FAIL_NO_MATCH (KEX)

Published 5 years ago

Hi all,

I am experiencing the "SSH_FAIL_NO_MATCH (KEX)", although I cannot find the reason for this...
According to the output I get on my C9300-24T Cisco switch during failed attempts, the KEX used by RDM by default should be supported, here are the settings and outputs:

Switch general info:

Switch  Ports    Model                Serial No.   MAC address     Hw Ver.       Sw Ver. 
------  -----   ---------             -----------  --------------  -------       --------
 1       41     C9300-24T             FCW2313GHMA  acf5.e637.bb80  V02           16.12.2s

Switch output on SSH key exchange failure:

Feb  5 09:24:27.423: %SSH-3-NO_MATCH: No matching kex algorithm found: client curve25519-sha256,curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group14-sha256,ext-info-c,ext-info-c server diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1changed

As you can see in above output, there are some KEX supported that should be part of the default suites in RDM...

Current output in RDM (custom with defaults selected):

When enabling every KEX in the list SSH (local) AAA works, for some reason the defaults don't work and I cannot figure out the reason for that. Please advise. Thanks a lot for the help!

KEX.PNG

SSH Algorithm Support

All Comments (3)

Samuel Dery

Published 5 years ago

Hello,

As per your "Switch output on SSH Key exchange failure" the following algorithms are being used by your server:

server diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1changed

In version 2020.3.13.0 and higher of Remote Desktop Manager unsecured algorithms are no longer enabled by default, simply enabling the remaining "Kex" algorithm should resolve your issue, This can also be done globally by going under "File" -> "Options" -> "Types" -> "Terminal" - > "Algorithm support"

We have an article on our knowledge base regarding this issue here is a link to it: https://kb.devolutions.net/rdm_ssh_algorithm_support.html

Best regards,

Samuel Dery

maximdelaet

Published 5 years ago

Hi Samuel,

Thanks a lot for the update, I managed to make it work in the default settings this time.

Interesting note however, I didn't manage to restore 1 of my sessions to default for algorithms (kept failing on login), I just ended up re-creating that session with the new defaults applied and that worked as well.

All good now.

Samuel Dery

Published 5 years ago

Hello,

I'm glad to hear that!

Best regards,

Samuel Dery