Fine-Tuning SSH/TELNET parameters

Fine-Tune SSH/telnet CLI parameters

The IP Fabric's discovery is primarily using Command Line Interface (CLI) to discover network elements. There are certain default CLI parameters that can be found in Settings → Advanced → SSH/TELNET:

Network device login timeout

Timeout before the logging prompt is received. It may take longer for remote branches over low-speed lines, or destined to overloaded devices.

Network device session timeout

Too many Command Timeout errors during the Discovery process may indicate that Network device session timeout is too short and it may be necessary to expect a delay for a response to arrive.

Maximum number of parallel sessions

To prevent flooding your network with too many SSH/TELNET sessions set Maximum number of parallel sessions. This setting can be also helpful if the AAA server (TACACS/Radius) has a limit of parallel AAA requests for users.

In rare cases, the Cisco ISE or similar systems may rate limit the command authorization. When there are too many authorization failures and Cisco ISE is in place, try to limit the number of parallel sessions down to 10 and steadily increase.

Basic failure

How many times to retry a connection for any error, except authentication failure.

Authentication failure

Authentication failure can occur even if a user is authorized to login but may happen, for example, when an AAA server is overloaded or an authentication packet is lost.

Command Authorization Failure retries

If you see many examples of Authentication error during the Discovery process, please adjust Authentication failure and Command Authorization Failure retries.

Example of error message in Connectivity Report

According to the summary of issues in the very first completed snapshot, the CLI Settings can be adjusted. Here are some of the most common errors and adjustments:

Error 

Error Type

How to mitigate

Error 

Error Type

How to mitigate

connect ETIMEDOUT XX.XX.XX.XX:22

Connection error

Received no response from the destination.

connect ECONNREFUSED XX.XX.XX.XX:22

Connection error

The connection to the destination is being blocked by an access-list or firewall.

All configured authentication methods failed

Authentication error

Unable to authenticate to the destination host

Authentication failed

Authentication error

Unable to authenticate to the destination host

Authentication failed - login prompt appeared again

Authentication error

Unable to authenticate to the destination host

SSH client not received any data for last 120000 ms! cmd => show vrrp  | e #^$

Command timeout

The command 'show vrrp  | e #^$' timed out. Increase device session timeout.

Can't detect prompt

Command timeout

Unable to detect CLI prompt. Increase network device login timeout.

Command "enable" authorization failed, tried 2x

Command authorization failure

The command wasn't authorized. Increase command authorization failure retries or increase the timer value (ms)