NCM Configuration Backup Fails on F5 BIG-IP Standby Node – SSH Login Succeeds but Prompt Is Not Accepted

8/3/2026 9:53 PM

8/3/2026 9:53 PM

Symptom

The Running Configuration backup on the F5 BIG-IP Standby node fails with the following error:

• ERROR: Running config: Unable to login to device: Timeout

The Active node backup completes successfully under the same connection profile, device template, and credentials.

When Session Tracing is enabled, the Standby node trace shows the following repeating loop until timeout:

• Custom Prompt detector detected a '>/#' prompt

• TimerTick: send CRLF to get the prompt

• (repeated)

• TimerTick: Login Timeout

In contrast, the Active node trace shows:

• Custom Prompt detector detected a '>/#' prompt

• Prompt being set to: [hostname]...(tmos)#

• Logged into device

• SendNextCommand Running: [first template command]

The prompt is received on the Standby node but NCM does not set it as the session prompt and does not execute any device template command.

Additional indicators:

• SNMP and ICMP polling are functional on the Standby node

• SSH connection and password authentication succeed on the Standby node

• The Credential Login Details show the TMOS prompt being returned repeatedly until the login timeout occurs

• The Credential Login Details may show the prompt with line breaks at different character positions across sessions

Environment

• SolarWinds NCM (all supported versions)

• F5 BIG-IP in Active/Standby HA configuration

• Device Template: F5 Big IP 12 and newer (or custom copy)

• Protocol: SSH

• F5 BIG-IP TMOS version 12 or later

Network Configuration Manager

The SolarWinds NCM F5 device template requires the F5 user account to have Terminal Access set to Advanced Shell. Using Traffic Management Shell (TMSH) is explicitly not supported for NCM F5 template operation.

Per the SolarWinds NCM F5 device template behavior documentation:

• Set the Terminal Access user on the device to Advanced Shell.

• Do not use Traffic Management Shell (TMSH).

When Terminal Access is TMSH, NCM may establish the login session successfully on the Active node but fail to establish it on the Standby node. This Active/Standby asymmetric behavior has been observed in multiple cases and is associated with differences in the TMOS prompt format between the two nodes. The Standby node's TMOS prompt includes the text "Standby" instead of "Active", which makes the prompt slightly longer. Community documentation reports that NCM's SSH session uses a default terminal width of 80 characters. When a TMOS prompt lands at or near this boundary, the F5 device wraps the cursor to a new line. NCM then sees the new line rather than the command prompt, and the repeated CRLF loop described above begins.

This same session trace pattern — prompt detected but login state never advancing, with repeated CRLF cycles until timeout — is documented for F5 Standby nodes in SolarWinds support case history.

Step 1 — Set F5 User Terminal Access to Advanced Shell (Primary Resolution)

Set the Terminal Access for the NCM service account on the F5 BIG-IP to Advanced Shell on both the Active and Standby nodes.

With Advanced Shell configured, the user logs directly into the bash shell upon SSH connection. The bash prompt is significantly shorter than the TMOS prompt and does not approach the SSH terminal width boundary. NCM establishes the session prompt reliably.

To configure Terminal Access on F5 BIG-IP, refer to the F5 BIG-IP documentation for your firmware version. The relevant setting is under System > Users > User List > [username] > Terminal Access. Set this to Advanced Shell.

Note: The steps above are based on F5 BIG-IP vendor documentation at the time of writing. SolarWinds does not own or maintain F5 BIG-IP user interface or documentation. Kindly refer to the official F5 documentation for the most current steps applicable to your firmware version.

After the change, retest the NCM Running Configuration backup on the Standby node.

The <Command Name="RESET" Value="run /util bash" RegEx="#"/> line in the device template can be retained or removed. When the user starts directly in bash via Advanced Shell, this command is no longer required for session establishment.

This step does not require SolarWinds service restart or monitoring downtime.

Step 2 — Add a VirtualPrompt Command to the Device Template (Secondary Workaround)

If setting Terminal Access to Advanced Shell is not immediately feasible, a supported workaround is to add a VirtualPrompt command to the custom device template assigned to the Standby node.

Add the following line to the device template (before or at the top of the command list):

<Command Name="VirtualPrompt" Value="#"/>

This instructs NCM to directly recognize any line containing '#' as the command mode prompt during the login stage, using the VirtualPrompt mechanism instead of the default prompt detection logic. Per the SolarWinds NCM device template commands documentation, VirtualPrompt is used to identify the command mode prompt when the device does not present a standard prompt ending in > or #.

Note: This is a template-level workaround and does not address the underlying Terminal Access configuration requirement. Step 1 is the primary supported resolution.

This step does not require SolarWinds service restart or monitoring downtime.

Step 3 — Increase CLI Prompt Timeout (Supporting Adjustment)

As a supporting measure, increase the Telnet/SSH Prompt Timeout:

• Go to Settings > All Settings > Product Specific Settings > CLI Settings

• Increase Telnet/SSH Prompt Timeout from the default value (for example, to 30 seconds)

• Click Submit

This step alone does not resolve the root cause. It is recommended as a supporting adjustment alongside Step 1 or Step 2.

This step does not require SolarWinds service restart or monitoring downtime.