From: David Laight <David.Laight@ACULAB.COM>
To: 'Xin Long' <lucien.xin@gmail.com>,
network dev <netdev@vger.kernel.org>,
"davem@davemloft.net" <davem@davemloft.net>,
"kuba@kernel.org" <kuba@kernel.org>,
Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>,
"linux-sctp@vger.kernel.org" <linux-sctp@vger.kernel.org>
Subject: RE: [PATCHv2 net-next 00/14] sctp: implement RFC8899: Packetization Layer Path MTU Discovery for SCTP transport
Date: Tue, 22 Jun 2021 22:13:14 +0000 [thread overview]
Message-ID: <cfaa01992d064520b3a9138983e8ec41@AcuMS.aculab.com> (raw)
In-Reply-To: <cover.1624384990.git.lucien.xin@gmail.com>
From: Xin Long
> Sent: 22 June 2021 19:05
>
> Overview(From RFC8899):
>
> In contrast to PMTUD, Packetization Layer Path MTU Discovery
> (PLPMTUD) [RFC4821] introduces a method that does not rely upon
> reception and validation of PTB messages. It is therefore more
> robust than Classical PMTUD. This has become the recommended
> approach for implementing discovery of the PMTU [BCP145].
>
> It uses a general strategy in which the PL sends probe packets to
> search for the largest size of unfragmented datagram that can be sent
> over a network path. Probe packets are sent to explore using a
> larger packet size. If a probe packet is successfully delivered (as
> determined by the PL), then the PLPMTU is raised to the size of the
> successful probe. If a black hole is detected (e.g., where packets
> of size PLPMTU are consistently not received), the method reduces the
> PLPMTU.
This seems to take a long time (probably well over a minute)
to determine the mtu.
What is used for the actual mtu while this is in progress?
Does packet loss and packet retransmission cause the mtu
to be reduced as well?
I can imagine that there is an expectation (from the application)
that the mtu is that of an ethernet link - perhaps less a PPPoE
header.
Starting with an mtu of 1200 will break this assumption and may
have odd side effects.
For TCP/UDP the ICMP segmentation required error is immediate
and gets used for the retransmissions.
This code seems to be looking at separate timeouts - so a lot of
packets could get discarded and application timers expire before
if determines the correct mtu.
Maybe I missed something about this only being done on inactive
paths?
David
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Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2021-06-22 22:13 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-22 18:04 [PATCHv2 net-next 00/14] sctp: implement RFC8899: Packetization Layer Path MTU Discovery for SCTP transport Xin Long
2021-06-22 18:04 ` [PATCHv2 net-next 01/14] sctp: add pad chunk and its make function and event table Xin Long
2021-06-22 18:04 ` [PATCHv2 net-next 02/14] sctp: add probe_interval in sysctl and sock/asoc/transport Xin Long
2021-06-22 18:04 ` [PATCHv2 net-next 03/14] sctp: add SCTP_PLPMTUD_PROBE_INTERVAL sockopt for sock/asoc/transport Xin Long
2021-06-22 18:04 ` [PATCHv2 net-next 04/14] sctp: add the constants/variables and states and some APIs for transport Xin Long
2021-06-22 18:04 ` [PATCHv2 net-next 05/14] sctp: add the probe timer in transport for PLPMTUD Xin Long
2021-06-22 18:04 ` [PATCHv2 net-next 06/14] sctp: do the basic send and recv for PLPMTUD probe Xin Long
2021-06-22 18:04 ` [PATCHv2 net-next 07/14] sctp: do state transition when PROBE_COUNT == MAX_PROBES on HB send path Xin Long
2021-06-22 18:04 ` [PATCHv2 net-next 08/14] sctp: do state transition when a probe succeeds on HB ACK recv path Xin Long
2021-06-22 18:04 ` [PATCHv2 net-next 09/14] sctp: do state transition when receiving an icmp TOOBIG packet Xin Long
2021-06-22 18:04 ` [PATCHv2 net-next 10/14] sctp: enable PLPMTUD when the transport is ready Xin Long
2021-06-22 18:04 ` [PATCHv2 net-next 11/14] sctp: remove the unessessary hold for idev in sctp_v6_err Xin Long
2021-06-22 18:04 ` [PATCHv2 net-next 12/14] sctp: extract sctp_v6_err_handle function from sctp_v6_err Xin Long
2021-06-22 18:04 ` [PATCHv2 net-next 13/14] sctp: extract sctp_v4_err_handle function from sctp_v4_err Xin Long
2021-06-22 18:05 ` [PATCHv2 net-next 14/14] sctp: process sctp over udp icmp err on sctp side Xin Long
2021-06-22 18:40 ` [PATCHv2 net-next 00/14] sctp: implement RFC8899: Packetization Layer Path MTU Discovery for SCTP transport patchwork-bot+netdevbpf
2021-06-22 22:13 ` David Laight [this message]
2021-06-23 1:09 ` Xin Long
2021-06-23 3:48 ` Xin Long
2021-06-23 9:50 ` David Laight
2021-06-23 15:59 ` Xin Long
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