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Message-Id: <20211104144203.3581611-1-anssi.hannula@bitwise.fi>
Date: Thu, 4 Nov 2021 16:42:05 +0200
From: Anssi Hannula <anssi.hannula@...wise.fi>
To: netdev@...r.kernel.org
Cc: stephen@...workplumber.org, Phil Sutter <phil@....cc>,
Hiroaki SHIMODA <shimoda.hiroaki@...il.com>
Subject: [PATCH iproute2] man: tc-u32: Fix page to match new firstfrag behavior
Commit 690b11f4a6b8 ("tc: u32: Fix firstfrag filter.") applied in 2012
changed the "ip firstfrag" selector to not match non-fragmented packets
anymore.
However, the documentation added in f15a23966fff ("tc: add a man page
for u32 filter") in 2015 includes an example that relies on the previous
behavior (non-fragmented packet counted as first fragment).
Due to this, the example does not work correctly and does not actually
classify regular SSH packets.
Modify the example to use a raw u16 selector on the fragment offset to
make it work, and also make the firstfrag description more clear about
the current behavior.
Fixes: f15a23966fff ("tc: add a man page for u32 filter")
Signed-off-by: Anssi Hannula <anssi.hannula@...wise.fi>
Cc: Phil Sutter <phil@....cc>
Cc: Hiroaki SHIMODA <shimoda.hiroaki@...il.com>
---
I suspect the original behavior was intentional, but the new one has
been out for 9 years now so I guess it is too late to change again.
man/man8/tc-u32.8 | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/man/man8/tc-u32.8 b/man/man8/tc-u32.8
index fec9af7f..507589bd 100644
--- a/man/man8/tc-u32.8
+++ b/man/man8/tc-u32.8
@@ -427,7 +427,7 @@ Also minimal header size for IPv4 and lack of IPv6 extension headers is assumed.
IPv4 only, check certain flags and fragment offset values. Match if the packet
is not a fragment
.RB ( nofrag ),
-the first fragment
+the first fragment of a fragmented packet
.RB ( firstfrag ),
if Don't Fragment
.RB ( df )
@@ -644,7 +644,7 @@ tc filter add dev eth0 parent 1:0 protocol ip \\
tc filter add dev eth0 parent 1:0 protocol ip \\
u32 ht 800: \\
match ip protocol 6 FF \\
- match ip firstfrag \\
+ match u16 0 1fff at 6 \\
offset at 0 mask 0f00 shift 6 \\
link 1:
.EE
--
2.31.1
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