Gorry,
Gorry Fairhurst wrote on 09/02/2022 12:02:
The draft proposes to add bottom-of-the-stack functionality to a 25yo
protocol, via a mechanism which is known to cause substantial packet
loss on production networks (see rfc7872).
Yes, loss of packets that carry the HBH PMTU was discussed. In
particular, loss of DPLPMTUD probes.
It was discussed, and the draft includes some text which alludes to
this. One thing that's missing is an acknowledgement of the scale of
packet loss associated with HBH options which is detailed in RFC7872.
The reliability of the proposed mechanism was brought up several times
during discussion at WG level, e.g.
https://mailarchive.ietf.org/arch/msg/ipv6/QrfdW0omcigRdPy2VECa_82oAEY/
RFC8899, notes how that packet loss can impact classical PMTUD, but also
suggests how to handle this when using DPLPMTUD.
The difficulty with MTU negotiation is that getting the MTU wrong will
cause packet blackholing.
Much less so using DPLPMTUD?
In other words, the draft specifies a protocol enhancement whose
stated aims imply increased reliability, which depends on a mechanism
which is known to be highly unreliable in practice, and where
misconfiguration can cause serious reliability issues.
This is not P-S territory.
Wait, that's a pretty large brush being used here.
Yes, it is, just as the blast radius for potential problems caused by
changes to the bottom of a protocol stack is pretty wide.
Nick
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