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man: tc-u32: Fix page to match new firstfrag behavior 

Commit 690b11f4a6 ("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 f15a23966f ("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: f15a23966f ("tc: add a man page for u32 filter")
Signed-off-by: Anssi Hannula <anssi.hannula@bitwise.fi>
Cc: Phil Sutter <phil@nwl.cc>
Cc: Hiroaki SHIMODA <shimoda.hiroaki@gmail.com>
Acked-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
This commit is contained in:
Anssi Hannula 2021-11-04 16:42:05 +02:00 committed by Stephen Hemminger
parent af96c7b5dd
commit a787d9ae10
1 changed files with 2 additions and 2 deletions
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4
man/man8/tc-u32.8
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@ -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 IPv4 only, check certain flags and fragment offset values. Match if the packet
is not a fragment is not a fragment
.RB ( nofrag ), .RB ( nofrag ),
the first fragment the first fragment of a fragmented packet
.RB ( firstfrag ), .RB ( firstfrag ),
if Don't Fragment if Don't Fragment
.RB ( df ) .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 \\ tc filter add dev eth0 parent 1:0 protocol ip \\
u32 ht 800: \\ u32 ht 800: \\
match ip protocol 6 FF \\ match ip protocol 6 FF \\
match ip firstfrag \\ match u16 0 1fff at 6 \\
offset at 0 mask 0f00 shift 6 \\ offset at 0 mask 0f00 shift 6 \\
link 1: link 1:
.EE .EE