Contents

Introduction

This document describes how to troubleshoot a Secure Email Gateway (SEG) is not able to join an existing cluster.

Prerequisited

Cisco recommends that you have knowledge of these topics:

- How to join appliances into a Cluster (Centralized Management).

- All ESAs must have the same AsyncOS versions (down to the revision).

Requirements

The information in this document was created from the devices in a specific lab enviroment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, ensure that you understand the potential of any command

Problem

The issue exists when joinging a Secure Email Gateway (SEG) to an existing cluster. The issue promt an error on connection, this is due to the ESA missing some of the kex algorithms/cipher algorithms.

Failed to join the cluster.

Error was: "(3, 'Could not find matching key exchange algorithm.')"

Enter the IP address of a machine in the cluster.

Solution

It is required to use the default values for sshconfig

esa> sshconfig

Choose the operation you want to perform:

- SSHD - Edit SSH server settings.

- USERKEY - Edit SSH User Key settings

- ACCESS CONTROL - Edit SSH whitelist/blacklist

[]> sshd

ssh server config settings:

Public Key Authentication Algorithms:

rsa1

ssh-dss

ssh-rsa

Cipher Algorithms:

aes128-ctr

aes192-ctr

aes256-ctr

aes128-cbc

3des-cbc

blowfish-cbc

cast128-cbc

aes192-cbc

aes256-cbc

rijndael-cbc@lysator.liu.se

MAC Methods:

hmac-md5

hmac-sha1

umac-64@openssh.com

hmac-ripemd160

hmac-ripemd160@openssh.com

hmac-sha1-96

hmac-md5-96

Minimum Server Key Size:

1024

KEX Algorithms:

diffie-hellman-group-exchange-sha256

diffie-hellman-group-exchange-sha1

diffie-hellman-group14-sha1

diffie-hellman-group1-sha1

ecdh-sha2-nistp256

ecdh-sha2-nistp384

ecdh-sha2-nistp521

To apply the default values you can run the command from the CLI > sshconfig > sshd on the step-by-step setup:

[]> setup

Enter the Public Key Authentication Algorithms do you want to use

[rsa1,ssh-dss,ssh-rsa]>rsa1,ssh-dss,ssh-rsa

Enter the Cipher Algorithms do you want to use

[aes128-ctr,aes192-ctr,aes256-ctr,aes128-cbc]>aes128-ctr,aes192-ctr,aes256-ctr,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,rijndael-cbc@lysator.liu.se

aes128-ctr,aes192-ctr,aes256-ctr,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,rijndael-cbc@lysator.liu.se

Enter the MAC Methods do you want to use

[hmac-md5,hmac-sha1,umac-64@openssh.com,hmac-ripemd160]>hmac-md5,hmac-sha1,umac-64@openssh.com,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96, diffie-hellman-group14-sha1

Enter the Minimum Server Key Size do you want to use

[1024]>

Enter the KEX Algorithms do you want to use

[diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1]>diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,iffie-hellman-group1-sha1,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521

Commit the changes

esa> commit

Please enter some comments describing your changes:

[]> Edit the SSHD values

After the change, the appliance joins the cluster successfully

Related Information

Configure an Email Security Appliance (ESA) Cluster

ESA FAQ: What are the requirements for setting up a cluster?