Data transfer is failing across a connection that is protected by an advanced firewall. The firewall uses signature-based detection. Relevant features may have names like antivirus, anti-spyware, intrusion prevention, or application control.
This may affect any make or model of firewall with similar features, but support cases have been opened for:
- Check Point
- Dell SonicWALL
- Fortinet appliances
- Palo Alto
Any type of data transfer may be affected. This problem may manifest in a wide variety of error messages and failure patterns. It may appear random, or consistently.
For the Veeam Backup & Replication product, this can affect Backup, Backup Copy, and Replication jobs. One common failure pattern is for the transfer of specific VM disks to consistently fail at or around the same percentage of completion.
Common error messages include:
An existing connection was forcibly closed by the remote host.
Unstable connection: unable to transmit data.
Depending on the job type and the version of Veeam Backup & Replication, connection failures may cause the job to fail immediately, or the connection may retry several times. While the connection is retried, the job may appear to be frozen because it is unable to transmit data. For more information, see:
Resume on Disconnect
Backup Copy: Automatic Job Retries
WAN Acceleration: Data Transport on WAN Disconnect
With Veeam Backup for Microsoft 365 this issue may appear with an error message:
A blocking operation was interrupted by a call to WSACancelBlockingCall