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Reducing APS Switchover Time in Layer 2 Circuits

On M320 routers with Channelized OC3/STM1 Circuit Emulation PIC with SFP, you can configure the fast-aps-switch statement at the [edit interfaces interface-name sonet-options aps] hierarchy level to reduce the Automatic Protection Switching (APS) switchover time in Layer 2 circuits. Configuring this statement reduces the APS switchover time only when the Layer 2 circuit encapsulation type for the interface receiving traffic from a Layer 2 circuit neighbor is Structure Agnostic time-division multiplexing (TDM) over Packet (SAToP).

The fast-aps-switch statement must be configured on both working and protect circuits. Additionally, to achieve reduction in APS switchover time:

• Per-packet load balancing must be configured.
• Bidirectional switching mode must be configured.
• If the fast-aps-switch statement is configured in revertive APS mode, configure an appropriate value for revert time. We recommend that you configure a revert time of 600 seconds for 672 through 1344 Layer 2 circuits.
• To prevent the logical interfaces in the data path from being shut down, configure appropriate hold-time values on all the interfaces in the data path that support TDM.

The fast-aps-switch statement cannot be configured when the APS annex-b option is configured. The interfaces that have the fast-aps-switch statement configured cannot be used in virtual private LAN service (VPLS) environments.

The following tasks illustrate how to configure Junos OS to reduce APS switchover time.

Note: Per-packet load balancing can be configured for a limited set of routes or for all routes. To simplify the steps involved in configuring per-packet load balancing, steps for configuring per-packet load balancing for all routes is covered in this procedure.

Configuring Per-Packet Load Balancing

1. Configure the per-packet option for the load-balance statement at the [edit policy-options policy-statement policy-name then] hierarchy level.
   [edit policy-options policy-statement policy-name then]user@host# set load-balance per-packet

   For example:

   [edit policy-options policy-statement load-balancing-policy then]user@host# set load-balance per-packet
2. Configure the policy name in the export statement at the [edit routing-options forwarding-table] hierarchy level.
   [edit routing-options forwarding-table]user@host# set export policy-name

   For example:

   [edit routing-options forwarding-table]user@host# set export load-balancing-policy

Configuring Fast APS Switchover

1. On both the working and protect circuits, configure the fast-aps-switch statement at the [edit interfaces interface-name sonet-options aps] hierarchy level.
   [edit interfaces interface-name sonet-options aps]user@host# set fast-aps-switch

   For example:

   [edit interfaces cstm1-0/0/0 sonet-options aps]user@host# set fast-aps-switch
   [edit interfaces cstm1-0/1/0 sonet-options aps]user@host# set fast-aps-switch
2. Configure bidirectional switching mode on both the working and protect circuits. To do this, configure the switching-mode bidirectional statement at the [edit interfaces interface-name sonet-options aps] hierarchy level on both the working and protect circuits.
   [edit interfaces interface-name sonet-options aps]user@host# set switching-mode bidirectional

   For example:

   [edit interfaces cstm1-0/1/0 sonet-options aps]user@host# set switching-mode bidirectional
   [edit interfaces cstm1-0/1/0 sonet-options aps]user@host# set switching-mode bidirectional
3. If APS is configured in revertive mode, configure an appropriate value for revert time on both the working and protect circuits. To do this, configure the revert-time statement at the [edit interfaces interface-name sonet-options aps] hierarchy level on both the working and protect circuits.
   [edit interfaces interface-name sonet-options aps]user@host# set revert-time seconds

   For example:

   [edit interfaces cstm1-0/0/0 sonet-options aps]user@host# set revert-time 600
   [edit interfaces cstm1-0/1/0 sonet-options aps]user@host# set revert-time 600
4. To prevent the logical interfaces in the data path from being shut down, configure appropriate hold-time values on all interfaces in the data path that support TDM.
   [edit interfaces interface-name hold-time]user@host# set up seconds down seconds

   For example:

   [edit interfaces cstm1-0/0/0 hold-time]user@host# set up 1 down 400