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[iproute2-next,v2,2/3] man: tc-pedit: Add examples for dsfield and retain

Message ID 4a1f881e2dce535e3848dd87914db41f80fd0d57.1585954968.git.petrm@mellanox.com
State Accepted
Delegated to: David Ahern
Headers show
Series Support pedit of ip6 traffic_class | expand

Commit Message

Petr Machata April 3, 2020, 11:05 p.m. UTC 
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@mellanox.com>
---
 man/man8/tc-pedit.8 | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)
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Patch

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),