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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.]

  • SRv6 network programming in IS-IS (MX Series with MPC10 and MPC11 line cards)—Starting in Junos OS Release 21.1R1, you can configure segment routing in a core IPv6 network without an MPLS data plane. This feature is useful for service providers whose networks are predominantly IPv6 and have not deployed MPLS. Such networks depend only on the IPv6 headers and header extensions for transmitting data. This feature also benefits networks that need to deploy segment routing traffic through transit routers that do not have segment routing capability yet. In such networks, the SRv6 network programming feature can provide the flexibility to leverage segment routing without deploying MPLS.

    To enable SRv6 network programming in an IPv6 domain, include the srv6 statement at the[edit routing-options source-packet-routing] hierarchy level.

    To advertise the Segment Routing Header (SRH) locator with a mapped flexible algorithm, include the algorithm statement at the [edit protocols isis source-packet-routing srv6 locator] hierarchy level.

    To configure a topology-independent loop-free alternate (TI-LFA) backup path for SRv6 in an IS-IS network,include the transit-srh-insert statement at the [edit protocols isis source-packet-routing srv6] hierarchy level.

    [See How to Enable SRv6 Network Programming in IS-IS Networks.]

  • Support for flexible algorithms in IS-IS for segment routing–traffic engineering (SR-TE) (ACX 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 the IGP metric and another flexible algorithm to compute a path based on the traffic engineering metric to divide the network into separate planes. This feature enables networks without a controller to configure traffic engineering and utilize the 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 isis segment routing] hierarchy level.

    [See Understanding IS-IS Flexible Algorithm for Segment Routing.]

  • Support for flexible algorithm in OSPFv2 for segment routing traffic engineering (ACX5448, ACX710, MX204, MX104, MX480, MX960, MX10003, MX2020, and PTX10001)—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.]