[Bug 278666] [sctp] Heartbeat jittering is not +- anymore

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=278666

            Bug ID: 278666
           Summary: [sctp] Heartbeat jittering is not +- anymore
           Product: Base System
           Version: Unspecified
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: kern
          Assignee: bugs@FreeBSD.org
          Reporter: albin.hellqvist@ericsson.com

Hi,

When reading the SCTP RFC regarding the SCTP heartbeat timing, it says:
"On an idle destination address that is allowed to heartbeat, it is RECOMMENDED
that a HEARTBEAT chunk is sent once per RTO of that destination address plus
the protocol parameter 'HB.interval', with jittering of +/- 50% of the RTO
value and exponential backoff of the RTO if the previous HEARTBEAT chunk is
unanswered."

It was implemented like this previously, but it was later changed here:
https://cgit.freebsd.org/src/commit/?id=70e95f0b6917a8b8cd4a2a5f883f3e9753fc86d8

I am wondering if this can be considered a bug? Because previously, the jitter
could be like [-RTO/2, RTO/2], but now it is [0, RTO/2]. This results in a
longer path failover on average for idle paths that are not sending DATA chunks
and receiving SACK:s.

Thank you in advance!

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