DCB-REWR(8) Linux DCB-REWR(8)
NAME
dcb-rewr - show / manipulate the rewrite table of the DCB (Data Center
Bridging) subsystem
SYNOPSIS
dcb [ OPTIONS ] rewr { COMMAND | help }
dcb rewr { show | flush } dev DEV [ prio-dscp ] [ prio-pcp ]
dcb rewr { add | del | replace } dev DEV [ prio-dscp DSCP-MAP ]
[ prio-pcp PCP-MAP ]
DSCP-MAP := [ DSCP-MAP ] DSCP-MAPPING
DSCP-MAPPING := PRIO:{ DSCP | all }
PCP-MAP := [ PCP-MAP ] PCP-MAPPING
PCP-MAPPING := PRIO:PCP
DSCP := { 0 .. 63 }
PCP := { 0(nd/de) .. 7(nd/de) }
PRIO := { 0 .. 7 }
DESCRIPTION
dcb rewr is used to configure the rewrite table, in the DCB (Data Center
Bridging) subsystem. The rewrite table is used to rewrite certain val-
ues in the packet headers, based on packet priority.
DCB rewrite entries are, like DCB APP entries, 3-tuples of selector,
protocol ID, and priority. Selector is an enumeration that picks one of
the prioritization namespaces. Currently, only the DSCP and PCP selector
namespaces are supported by dcb rewr.
The rewrite table is a list of DCB rewrite rules, that applies to pack-
ets with matching priority. Notably, it is valid to have conflicting
rewrite assignment for the same selector and priority. For example, the
set of two rewrite entries (DSCP, 10, 1) and (DSCP, 11, 1), where pack-
ets with priority 1 should have its DSCP value rewritten to both 10 and
11, form a well-defined rewrite table. dcb rewr tool allows low-level
management of the rewrite table by adding and deleting individual
rewrite 3-tuples through add and del commands. On the other hand, the
command replace does what one would typically want in this situa-
tion--first adds the new configuration, and then removes the obsolete
one, so that only one rewrite rule is in effect for a given selector and
priority.
COMMANDS
show Display all entries with a given selector. When no selector is
given, shows all rewrite table entries categorized per selector.
flush Remove all entries with a given selector. When no selector is
given, removes all rewrite table entries.
add
del Add and, respectively, remove individual rewrite 3-tuples to and
from the DCB rewrite table.
replace
Take the list of entries mentioned as parameter, and add those
that are not present in the rewrite table yet. Then remove those
entries, whose selector and priority have been mentioned as para-
meter, but not with the exact same protocol ID. This has the ef-
fect of, for the given selector and priority, causing that the
table only contains the protocol ID (or ID's) given as parameter.
PARAMETERS
The following table shows parameters in a way that they would be used
with add, del and replace commands. For show and flush, the parameter
name is to be used as a simple keyword without further arguments.
prio-dscp DSCP-MAP
DSCP-MAP uses the array parameter syntax, see dcb(8) for details.
Keys are priorities, values are DSCP points for traffic with
matching priority. DSCP points can be written either directly as
numeric values, or using symbolic names specified in
/etc/iproute2/rt_dsfield (however note that the file specifies
full 8-bit dsfield values, whereas dcb rewr will only use the
higher six bits). dcb rewr show will similarly format DSCP val-
ues as symbolic names if possible. The command line option -N
turns the show translation off.
prio-pcp PCP-MAP
PCP-MAP uses the array parameter syntax, see dcb(8) for details.
Keys are priorities. Values are PCP/DEI for traffic with matching
priority. PCP/DEI values are written as a combination of numeric-
and symbolic values, to accommodate for both. PCP always in nu-
meric form e.g 0 .. 7 and DEI in symbolic form e.g 'de' (drop-
eligible), indicating that the DEI bit is 1 or 'nd' (not-drop-el-
igible), indicating that the DEI bit is 0. In combination 1:2de
translates to a mapping of priority 1 to PCP=2 and DEI=1.
EXAMPLE & USAGE
Add a rule to rewrite DSCP to 0, 24 and 48 for traffic with priority 0,
3 and 6, respectively:
# dcb rewr add dev eth0 prio-dscp 0:0 3:24 6:48
Add a rule to rewrite DSCP to 25 for traffic with priority 3:
# dcb rewr add dev eth0 prio-dscp 3:25
# dcb rewr show dev eth0 prio-dscp
prio-dscp 0:0 3:CS3 3:25 6:CS6
# dcb -N rewr show dev eth0 prio-dscp
prio-dscp 0:0 3:24 3:25 6:48
Reconfigure the table so that only one rule exists for rewriting traffic
with priority 3.
# dcb rewr replace dev eth0 prio-dscp 3:26
# dcb rewr -N show dev eth0 prio-dscp
prio-dscp 0:0 3:26 6:48
Flush all DSCP rules:
# dcb rewr flush dev eth0 prio-dscp
# dcb rewr show dev eth0 prio-dscp
(nothing)
Add a rule to rewrite PCP to 1 and DEI to 0 for traffic with priority 1
and a rule to rewrite PCP to 2 and DEI to 1 for traffic with priority 2:
# dcb rewr add dev eth0 prio-pcp 1:1nd 2:2de
# dcb rewr show dev eth0 prio-pcp
prio-pcp 1:1nd 2:2de
EXIT STATUS
Exit status is 0 if command was successful or a positive integer upon
failure.
SEE ALSO
dcb(8) dcb-app(8) dcb-apptrust(8)
REPORTING BUGS
Report any bugs to the Network Developers mailing list <netdev@vger.ker-
nel.org> where the development and maintenance is primarily done. You
do not have to be subscribed to the list to send a message there.
AUTHOR
Daniel Machon <daniel.machon@microchip.com>
iproute2 15 may 2023 DCB-REWR(8)
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