https://bugs.kde.org/show_bug.cgi?id=446238
Bug ID: 446238
Summary: UDP broadcast to port 1716 is oversized due to
featureitis. the UDP payload size is 1900, the
ethernet MTU is 1500
Product: kdeconnect
Version: unspecified
Platform: Android
OS: Android 11.x
Status: REPORTED
Severity: normal
Priority: NOR
Component: android-application
Assignee: albertv...@gmail.com
Reporter: riegle...@a1.net
Target Milestone: ---
SUMMARY
***
tracing the ethernet frames with wireshark on Ubuntu 20.04 LTS shows UDP
broadcast to port 1716 with a payload size of about 1900.
I have a PF (personal firewall) in Ubuntu (native Linux subsystem nftables)
with a "stateless config"
all ethernet frames not having either TCP or UDP header is dropped for
security.
the UDP broadcast to port 1716 gets split into two IPv4 fragments (payload is
above MTU=1500).
my PF is dropping IPv4 fragments.
It seems that adding features has brought the payload size above MTU=1500. (my
assumption)
think about IoT with small HW and a limited IPv4 code (without IPv4 fragments,
without IPv4 options)
UDP must be simple. e.g. UDP DNS limits the 512 Bytes payload. IPv4 hat only a
size of 576 Bytes.
***
STEPS TO REPRODUCE
1. I use wireshark, just trace on the ethernet wire or WLAN and check the UDP
broadcast to UDP port 1716
2.
3.
OBSERVED RESULT
you see two IPv4 fragments, the first has the UDP header, the second not
EXPECTED RESULT
there needs to be a major rethinking of the "feature broadcast" to stay inside
the limits of the infrastructure.
the MTU=1500 - 20Bytes IPv4 - 8Bytes UDP needs a hard limit of 1472 Bytes for
the feature broadcast.
All OS platforms needs to adapt to a version2 of the "feature broadcast"
SOFTWARE/OS VERSIONS
Windows:
macOS:
Linux/KDE Plasma:
(available in About System)
KDE Plasma Version:
KDE Frameworks Version:
Qt Version:
ADDITIONAL INFORMATION
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