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Segment Routing

  • Avoid microloops in IS-IS-SRv6 networks (MX Series with MPC7E, MPC8E and MPC9E line cards) —Starting in Junos OS Release 21.1R1, you can enable post-convergence path calculation on a device to avoid microloops if a link or metric changes in an SRv6 network. Note that microloop avoidance is not a replacement for local repair mechanisms such as topology-independent loop-free alternate (TI-LFA), which detects local failure very fast and activates a precomputed loop-free alternative path.

    To configure microloop avoidance in an SRv6 network, include the microloop avoidance post-convergence-path delay milliseconds statement at the [edit protocols isis spf-options] hierarchy level.

    [See How to Configure Microloop Avoidance for IS-IS in SRv6 Networks.]
  • Support for flexible algorithm in OSPFv2 for segment routing traffic engineering (ACX Series, MX Series, and PTX Series)—Starting in Junos OS Release 21.1R1, you can thin-slice a network by defining flexible algorithms that compute paths using different parameters and link constraints based on your requirements. For example, you can define a flexible algorithm that computes a path to minimize IGP metric and define another flexible algorithm to compute a path based on traffic engineering metric to divide the network into separate planes. This feature allows networks without a controller to configure traffic engineering and utilize segment routing capability of a device.

    To define a flexible algorithm, include the flex-algorithm statement at the [edit routing-options] hierarchy level.

    To configure a device to participate in a flexible algorithm, include the flex-algorithm statement at the [edit protocols ospf source-packet-routing] hierarchy level.

    [See How to Configure Flexible Algorithms in OSPF for Segment Routing Traffic Engineering.]

  • Support for strict SPF and IGP shortcut (ACX710, MX960, MX10008, MX2020, PTX5000, and PTX1000)—Starting in Junos OS Release 21.1R1, you can configure segment routing algorithm 1 (strict SPF) and advertise its SIDs in IS-IS link-state PDU (LSPDU) and use these SIDs to create SR-TE tunnels to forward the traffic by using the shortest IGP path to reach the tunnel endpoint while avoiding loops. You can also specify a set of prefixes in the import policy, based on which the tunnel can redirect the traffic to a certain destination. You can use algorithm 1 (strict SPF) along with algorithm 0 (default SPF) by default when Source Packet Routing in Networking (SPRING) is enabled.

    [See How to Enable Strict SPF SIDs and IGP Shortcut, prefix-segment, and source-packet-routing.]