TC syntax for DSCP set, difficulty: Linux 2.6.22

Installing and Using OpenWrt
1

This is not exactly an OpenWRT question but since Broadcom based devices are natively stuck on Linux 2.6.22 or thereabouts, still a current one:

I'd like to use DSCP VOICE-ADMIT 44=0x2c for some voip connections. But the syntax in this ancient tc version is difficult, tc here won't even support "action pedit munge ip tos set". Please I do know how to do it with iptables, this is all about doing it with tc.

I've googled everything since 15 year old mail list messages and everything I can find, only to find almost nothing at all.
Found this mailing list message explaining part of what might be the problem, the date might put this a bit later than 2.6.22 so the bug might manifest itself here, although the mailing list "ok" example won't run either:

https://www.spinics.net/lists/netdev/msg190368.html
Subject: [PATCH iproute] tc pedit action: fix parsing offset options.
Date: Wed, 29 Feb 2012 19:34:28 +0300
This patch fix parsing offset option with "at" parameter.
Tc returns error If keywords "offmask" and "shift" are presented.

Error: action pedit munge offset 2 u16 at 0 offmask 0f0000000 shift 22 set 11500
Ok: action pedit munge offset 2 u16 at 0 0f0000000 22 set 11500

But no variation I try seems to get it right, match u8 0 0 is here for example only to keep the focus on pedit:

# tc filter add dev ppp0 parent 8:0 protocol ip prio 999 u32 match u8 0 0 \
action pedit munge offset 0 u8 at 1 0xff 0 set 0x2c

parse_cmd argc 2 set offset 0 length 1
pack_key8: Final word off 0 val 0000002c mask ffffff00
parse_cmd done argc 0 (null) offset 0 length 1
RTNETLINK answers: Invalid argument
We have an error talking to the kernel

# tc filter add dev ppp0 parent 8:0 protocol ip prio 999 u32 match u8 0 0 \
action pedit munge offset 0 u16 at 0 0x00ff 0 set 0x2c

parse_cmd argc 2 set offset 0 length 2
pack_key16: Final val 00002c00 mask ffff0000
parse_cmd done argc 0 (null) offset 0 length 2
RTNETLINK answers: Invalid argument
We have an error talking to the kernel

# tc filter add dev ppp0 parent 8:0 protocol ip prio 999 u32 match u8 0 0 \
action pedit munge offset 0 u32 at 0 0x00ff0000 16 set 0x2c

parse_cmd argc 2 set offset 0 length 4
parse_cmd done argc 0 (null) offset 0 length 4
RTNETLINK answers: Invalid argument
We have an error talking to the kernel

Old memories and smart brains welcome :wink:

2

@ml70, welcome to the community!

Who told you that?

Nope, not true, nor relevant question for OpenWrt. OpenWrt's not stuck on that kernel - that very old. The current release candidate ( v19.07.0-rc2) is on v 4.9.100.

See: https://openwrt.org/meta/infobox/broadcom_wifi

So, on to your issue:

  • Are you trying to flag traffic for DSCP in OpenWrt or something?
3

The OpenWrt builds for Broadcom chips are the same recent kernels as other chips, but wifi driver support is often limited or none. In a wired application these chips work fine.

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4

Just to extend the answers given above, beyond the challenging wireless situation, xDSL/ cable/ fibre modem or FXS support usually doesn't exist at all for Broadcom chips.

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