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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?



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    Justin Melloni
    Documentation/Training Specialist
    MA
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  • 2.  RE: What are the Session Resiliency settings?

     
    Posted 12-04-2018 15:34

    The Session-Resiliency setting applies when there are multiple paths available between a pair of 128T peers (two routers peering using the 128T secure vector routing technique). The setting refers to how established flows behave in terms of utilizing available paths.

    The "none" setting means that each session will utilize one, and only one, path during its lifetime. If the path becomes impaired, any established sessions with the "none" setting will not be failed over to another path. Even if the path experiences a hard down, those sessions will be terminated and removed.

    The "failover" option will ensure that sessions are seamlessly migrated to the next best available path, per the various policies configured, if the current path experiences a hard down, or its QoS measurements no longer meet the session's SLA requirements configured in its associated service policy.

    The "revertible-failover" option will act as the previous option, with the exception that if the original impaired path comes back in service, the migrated session will be moved back to that original path. This sometimes has the potential of session flapping back and forth between paths, so may not always be appropriate.

    Finally, "packet-duplication" sends all of the session's packets over multiple available path, and duplicate copies of those packets are discarded at the receiving end. Packet-duplication is obviously more taxing on the total available bandwidth between a pair of peers, but can substantially improve QoS/MOS measurements compared to utilizing just one path .



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    Gene Shtirmer
    Sales Engineer
    Burlington MA
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  • 3.  RE: What are the Session Resiliency settings?

    Posted 12-04-2018 15:35
    @Gene - Thanks for the explanation, I've been looking for this for sometime now! - I was curious if packet-duplication is valid only for UDP traffic?

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    Jessie Bryan
    VP Engineering
    CA
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  • 4.  RE: What are the Session Resiliency settings?

     
    Posted 12-04-2018 15:36
    @Jessie, you are absolutely correct, UDP is the only transport protocol supported for packet-duplication. If you have a service, which has both UDP and TCP, you'll want to break it up into two services, and enable the UDP one for packet duplication, while the TCP one would use something else, such as failover.

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    Gene Shtirmer
    Sales Engineer
    Burlington MA
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  • 5.  RE: What are the Session Resiliency settings?

    Posted 12-04-2018 15:37
    That's what I thought @Gene​, and that must also mean packet-duplication requires an inter-128T / SVR session-path? Without this, packet-duplication policy could not function (and probably won't work for service-routes using non-128T next-hops)

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    Jessie Bryan
    VP Engineering
    CA
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  • 6.  RE: What are the Session Resiliency settings?

     
    Posted 12-04-2018 15:37
    @Jessie, that's precisely correct. We are working on some additional functionality to support non-SVR next-hop failover, which may work "mid-session" in some, but not all, cases, for example where you don't care about preserving tcp state.

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    Gene Shtirmer
    Sales Engineer
    Burlington MA
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