Avamar: Putty connection fails due to "Couldn't agree a client-to-server cipher"

Summary: Unable to make a putty connection due to error "Couldn't agree a client-to-server cipher."

This article applies to This article does not apply to This article is not tied to any specific product. Not all product versions are identified in this article.
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Symptoms

Unable to use PuTTY to connect to an Avamar grid after an upgrade.

Connections fail with the following error:

Putty Fatal Error

 
Note: This issue has also been observed with other Dell Products.

Cause

When the Operating System (OS) is upgraded, it updates the /etc/ssh/ssh_config file with ciphers that older versions of PuTTY do not support.

PuTTY versions earlier than v.59 do not include the CTR layer encryption mode required to communicate with the updated Avamar grid.

 

Resolution

Update the version of PuTTY to a later version (the recommended version is v.67 or higher):

1. Go to the PuTTY download page. http://www.chiark.greenend.org.uk/~sgtatham/putty/download.html (External Link)

2. Select an applicable version (and type) of PuTTY for your environment.

3. Download and install PuTTY.

Note: If the download page is blocked, or elevated privileges are required to install programs, customers must seek assistance from their local IT teams to update the PuTTY version.
 

4. Test the connection to the Avamar grid.

Affected Products

Avamar, Avamar Server, Dell EMC Unity Family

Products

Avamar
Article Properties
Article Number: 000169727
Article Type: Solution
Last Modified: 02 Oct 2025
Version:  10
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