14.1.2 Operation of GSRP switching

When switching on GSRP switch, you cannot immediately resume end-to-end communication by simply controlling the switching of forwarding and blocking for the frame. However, that is not enough to immediately resume end-to-end communication, because the MAC address entries in the MAC address tables in the neighboring switches are still registered for the previous master GSRP switch. To immediately resume communication, the MAC address table entries on the neighboring switches need to be cleared when the GSRP switches change.

When GSRP switch is used for switching, a control frame called a GSRP Flush request frame is transmitted to request clearing of MAC address table entry from the surrounding switch. A switch that can receive this GSRP Flush request frame and clear the internal MAC address table is GSRP aware. The Switch operates as a GSRP aware at all times. GSRP-aware switches flood GSRP Flush request frames. The following figure shows the operation for GSRP Flush request frame reception.

Figure 14-2 Actions when receiving GSRP Flush request frames

1. Switching is performed between GSRP Switch A and GSRP Switch B, and GSRP Flush request frames are sent to the Switch.

2. The Switch receives GSRP Flush request frame and clears MAC address table in the Switch.

3. Consequently, the Switch floods the frames sent by PC until MAC addressing is learned.

   The frame is forwarded to the destination through GSRP Switch-B, which is the master.

4. When a frame addressed to PC is returned, the Switch learns MAC addressing information.

   Thereafter, the Switch forwards frames from PC only toward GSRP B.