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Ask questions and share experiences with SD-WAN and Session Smart Router (formerly 128T).
  • 1.  What are the Session Resiliency settings?

    Posted 12-04-2018 15:29

    In the Service Policy, there are 4 settings under Session Resiliency:

    • none
    • failover
    • revertible-failover
    • packet-duplication


    What does each setting do?

    Justin Melloni
    Documentation/Training Specialist

  • 2.  RE: What are the Session Resiliency settings?

    Posted 12-05-2018 12:45
    These control how a 128T treats sessions when a peer path (a peering association from one router to another) gets interrupted.

    When session-resiliency = none, a failed peer path takes down the sessions with it.
    When session-resiliency = failover, a 128T will treat ensuing packets for that session as "first packets" in the event of a peer path failure, and re-trigger metadata generation to choose another path for the session.
    When session-resiliency = revertible-failover, the 128T will behave as it does in "failover," but revert back to the original path if it is restored while the session is still in progress.
    When session-resiliency = packet-duplication, the 128T sends two copies of each packet to its destination via separate peer paths. The recipient 128T drops any duplicates it receives. This can only be used with services that use UDP transport, and is typically used for RTP (voice) services to improve call quality when there are periods of loss/latency/jitter on one link.

    We've also recently added two new session-resiliency modes: packet-retransmission and packet-retransmission-with-dpi. These are used as sort of a "SACK" (selective ACK) feature, where routers can re-request packets that are lost in transit between one another. Perhaps @Michael Adams can talk about the difference between the regular and with-dpi variations... ​​​


  • 3.  RE: What are the Session Resiliency settings?

    Posted 05-09-2019 15:43
    Patrick, if a service didn't have a service policy assigned to it. What would be the default behavior for resiliency of that service?

    Cody Van Lith

  • 4.  RE: What are the Session Resiliency settings?

    Posted 05-09-2019 16:27

    Hey Cody,
    In general if no specific configuration is provided, the default values are used. In the case where no "service-policy" is assigned to a "service", then "session-resiliency" is "none".

    Adam Morris
    Sales Engineer
    (206) 617-4999