Troubleshooting Guide: SQL Server Error 3297 – Invalid URL Format

Why This Error Happens

Error 3297 occurs when SQL Server’s BACKUP or RESTORE command receives a URL (typically pointing to Azure Blob Storage) that does not conform to valid URI syntax. This is commonly caused by malformed container paths, missing or incorrect SAS token configurations, or a Credential object in SQL Server that references an outdated or improperly formatted endpoint. It can also occur if the storage account name or container path contains illegal characters or inconsistent casing that breaks absolute/relative URI resolution.

Step-by-Step Resolution Guide

Step 1: Validate the URL Syntax

• Confirm the URL follows the pattern: https://<storageaccountname>.blob.core.windows.net/<containername>/<filename>.bak
• Check for trailing slashes, double slashes, or missing https:// prefixes.
• Ensure there are no spaces or special characters (like #, %, or unescaped &) in the container or blob name.

Step 2: Verify the SQL Server Credential Object

• Run the following query to inspect existing credentials:

  SELECT * FROM sys.credentials;

• Ensure the CREDENTIAL name exactly matches the container URL (not just the storage account) if using a Shared Access Signature (SAS).
• Recreate the credential if needed:

  CREATE CREDENTIAL [https://yourstorageaccount.blob.core.windows.net/yourcontainer]
  WITH IDENTITY = 'SHARED ACCESS SIGNATURE',
  SECRET = 'your_sas_token_without_leading_question_mark';

Step 3: Check for Leading Characters in the SAS Token

• Open the SAS token used in the SECRET field of the credential.
• Remove any leading ? character, as SQL Server 2025 strictly parses the token and will reject it if present, indirectly triggering Error 3297 due to URI resolution failure.
• Re-run the backup/restore command after updating the token.

Step 4: Confirm Windows Server DNS Resolution

• On Windows Server 2025, open Command Prompt and run:

  nslookup yourstorageaccount.blob.core.windows.net

• If resolution fails, check the network adapter DNS settings in Control Panel > Network and Sharing Center > Change adapter settings.
• Ensure outbound port 443 is open via Windows Defender Firewall with Advanced Security.

Alternative or Verification Steps

• Test the fix by running a simple RESTORE FILELISTONLY FROM URL = '<your_url>' command; if it returns file metadata without error, the URL and credential are correctly configured.
• If the issue persists, try using a local UNC path for the backup/restore operation to isolate whether the problem is specific to the Azure URL/credential configuration rather than SQL Server itself.