kernel:err: CIFS VFS: cifs_mount failed w/return code = -115

The Problem

When mounting a remote CIFS shared volume, the following error is shown and the volume is not mounted:

# mount /<SHARED_VOLUME_MOUNTPOINT>
mount: mount //<IP-ADDRESS>/<SHARENAME> on /<SHARED_VOLUME_MOUNTPOINT> failed: Operation now in progress

It can be seen in the /var/log/messages file that the mount process fails with error 115:

kernel:err: CIFS VFS: Error connecting to socket. Aborting operation.
kernel:err: CIFS VFS: cifs_mount failed w/return code = -115

The Solution

CIFS error 115 most common cause is that the server is not accepting communications from the client in all needed ports. Server is the CIFS server hosting the share and client is the instance where it is being mounted.

To effectively mount a remote CIFS share, configure the remote server network to accept incoming connections from the client IP address. This includes the server’s internal firewall and any in-between firewalls betwwen the server and client, including the OCI security lists for the appropriate subnet configured to allow incoming connections from the client(s) IP address(es).

The CIFS server ports that have to be network enabled to accept traffic from the client are:

• Browsing datagram responses of NetBIOS over TCP/IP: 138/UDP
• Browsing requests of NetBIOS over TCP/IP: 137/UDP
• Client/Server Communication: 135/TCP
• Common Internet File System (CIFS): 445/UDP and 139,44/TCP

For OCI, for the subnet of the server’s IP address, ensure security rules for both ingress and egress exist, allowing traffic between the client IP and server IP for ports 135, 137, 138, 139, 44 and 445 - both TCP and UDP for simplicity.