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Message-Id: <4a1f881e2dce535e3848dd87914db41f80fd0d57.1585954968.git.petrm@mellanox.com>
Date: Sat, 4 Apr 2020 02:05:30 +0300
From: Petr Machata <petrm@...lanox.com>
To: netdev@...r.kernel.org
Cc: Petr Machata <petrm@...lanox.com>,
Stephen Hemminger <stephen@...workplumber.org>,
David Ahern <dsahern@...il.com>
Subject: [PATCH iproute2-next v2 2/3] man: tc-pedit: Add examples for dsfield and retain
Describe a way to update just the DSCP and just the ECN part of the
dsfield. That is useful on its own, but also it shows how retain works.
Signed-off-by: Petr Machata <petrm@...lanox.com>
---
man/man8/tc-pedit.8 | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)
diff --git a/man/man8/tc-pedit.8 b/man/man8/tc-pedit.8
index 3f6baa3d..d2b37ef0 100644
--- a/man/man8/tc-pedit.8
+++ b/man/man8/tc-pedit.8
@@ -369,6 +369,28 @@ tc filter add dev eth0 parent ffff: u32 \\
action pedit ex munge tcp dport set 22
.EE
.RE
+
+To rewrite just part of a field, use the
+.B retain
+directive. E.g. to overwrite the DSCP part of a dsfield with $DSCP, without
+touching ECN:
+
+.RS
+.EX
+tc filter add dev eth0 ingress flower ... \\
+ action pedit ex munge ip dsfield set $((DSCP << 2)) retain 0xfc
+.EE
+.RE
+
+And vice versa, to set ECN to e.g. 1 without impacting DSCP:
+
+.RS
+.EX
+tc filter add dev eth0 ingress flower ... \\
+ action pedit ex munge ip dsfield set 1 retain 0x3
+.EE
+.RE
+
.SH SEE ALSO
.BR tc (8),
.BR tc-htb (8),
--
2.20.1
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