Sending BecomeBackup Frames

A browser server whose Current Role is equal to local master browser MUST choose the number of browser servers whose Current Role is equal to backup browser server. The number of backup browser servers is a trade-off between:

  • Minimizing network traffic.

  • Ensuring robustness by having multiple backup browser servers.

  • Ensuring that when a local master browser server fails, there are multiple backup browser servers, which can become local master browser servers.<51>

If the local master browser server determines that one or more backup browser servers SHOULD be added to its Backup Browser List<52>, it MUST send BecomeBackup (section 2.2.6) frames to enough servers to get up to the recommended level of backup servers. Each server to which it sends a BecomeBackup frame MUST be in the local master browser's Servers List and MUST NOT be in the Backup Browser List. The server MUST send the BecomeBackup frame by issuing a mailslot write as specified in [MS-MAIL] section with the following parameters:

Parameter name


NetBIOS name of the remote server

< server to be promoted to backup >[0x00]

Mailslot name



BecomeBackup as specified in section 2.2.6.

The server SHOULD continue processing as described below even if the send fails.

The action to add one or more backup browser servers is triggered by the Server Expiration Timer as specified in Timer Events (section 3.3.6).