[tcpm] RFC2883 DSACK - duplicate SYN
"Scheffenegger, Richard" <rs.ietf@gmx.at> Mon, 09 September 2019 10:47 UTC
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To: "tcpm@ietf.org" <tcpm@ietf.org>
From: "Scheffenegger, Richard" <rs.ietf@gmx.at>
Message-ID: <1964a510-1356-e6ec-e7ff-df98f8f07a85@gmx.at>
Date: Mon, 09 Sep 2019 12:47:36 +0200
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Archived-At: <https://mailarchive.ietf.org/arch/msg/tcpm/I7XuG9WXMN3WzxX1L7lARpfj1Oc>
Subject: [tcpm] RFC2883 DSACK - duplicate SYN
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Hi,
Since RFC2883 is silent on the two special flags SYN and FIN, I wanted
to check with you if my understanding is correct:
If a FIN is received (pure or with data) after a gap in the sequence
space, as it consumes a sequence number, it becomes part of the SACK
block reported back to the sender.
So far, so good. But shouldn't the same also be happening for a
duplicate received SYN?
The sender announces that it supports SACK with the SYN, thus a receiver
could choose to send out a DSACK for a duplicate SYN. At least neither
RFC2018 nor RFC2883 are ruling this out:
SYN (SACK permitted) ->
<- SYN,ACK (SACK permitted)
(dup) SYN (SACK permitted) ->
<- SYN,ACK (SACK permitted, D-SACK for SYN)
ACK ->
Depending on the sequence of events, a sender could infer network
duplication, or very high RTT, unambigiously when doing a DSACK on a
SYN,ACK....
Best regards,
Richard
- [tcpm] RFC2883 DSACK - duplicate SYN Scheffenegger, Richard