From f91f788c70e92a80b53f8e6c83ac3059aa0b9ddc Mon Sep 17 00:00:00 2001 From: Petr Machata Date: Sat, 4 Apr 2020 02:05:30 +0300 Subject: [PATCH] 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 Signed-off-by: David Ahern --- 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 3f6baa3dd..d2b37ef07 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), -- 2.47.2