This article explains why an error message may be encountered while trying to SSH to a switch by using Putty, and describes the steps to resolve the error.
SSH to a switch by using a particular host is not successful when using “Putty/WinSCP” software for SSH.
The following log message is generated as shown by executing show log message :
show log message
sshd[14255]: error: Hm, kex protocol error: type 30 seq 1
This is an issue with old Putty software. The message "type 30" is a pre-RFC4419 group exchange message and support for the "type 30" message has been removed from OpenSSH release 6.1 and later.
When this default message in the Diffie-Hellman group exchange algorithm policy is used during SSH key exchange, it generates the above error message.
Perform the following steps to fix this problem:
Select “Diffie-Hellman group exchange” under "Algorithm selection policy" and move it to the bottom of the list, so that it is not used.
The connection should now start working normally again.