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-nistp521To 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?
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