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    Understanding the Broadband Gateway Anchor Failover Behavior

    The MobileNext Broadband Gateway anchor session Dense Port Concentrators (DPCs) (housing PICs) and interface PFEs can be configured for redundancy. However, due to the different nature of the redundancy involved, 1:1 for anchor session PICs and N:1 for anchor interface PFEs, the failover behavior is slightly different.

    Figure 1: Control Plane Anchor Operation Before Failure

    Control Plane Anchor Operation Before
Failure

    As shown in Figure 1, you can configure session DPCs with or without backup. In this case, MS0 has no backup redundancy, while both PICs (PIC0 and PIC1) on MS1 are backed up 1:1 by standby MS2. When the anchor session DPC MS1 fails, packets cannot be processed strictly by hardware data path until the transfer of control to the new anchor is complete. This is shown in Figure 2. Note that ams1 now points to MS2, the new active anchor.

    Figure 2: Control Plane Anchor Operation After Failure

    Control Plane Anchor Operation After
Failure

    However, data plane packets feature N:1 anchor data path redundancy. Both pre- and post-failure Packet Forwarding Engine data paths are shown in Figure 3. For clarity, only the active and standby Packet Forwarding Engines are shown.

    Figure 3: Pre- and Post-Failure PFE Datapaths

    Pre- and Post-Failure PFE Datapaths

    During the transition on the ingress and egress interface Packet Forwarding Engines sending data plane packets from the failed PFE1 to the new active PFE2, packets cannot be processed strictly by hardware data path until the transfer of control to the new anchor is complete.

    Published: 2011-11-22