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NAME | SYNOPSIS | DESCRIPTION | COMMANDS | PARAMETERS | EXAMPLE & USAGE | EXIT STATUS | SEE ALSO | REPORTING BUGS | AUTHOR | COLOPHON |
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DCB-REWR(8) Linux DCB-REWR(8)
dcb-rewr - show / manipulate the rewrite table of the DCB (Data
Center Bridging) subsystem
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 }
dcb rewr is used to configure the rewrite table, in the DCB (Data
Center Bridging) subsystem. The rewrite table is used to rewrite
certain values 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
packets 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 packets 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 situation--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.
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 parameter, but not with the exact same
protocol ID. This has the effect of, for the given selector
and priority, causing that the table only contains the
protocol ID (or ID's) given as parameter.
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 values 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 numeric 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-
eligible), indicating that the DEI bit is 0. In
combination 1:2de translates to a mapping of priority 1 to
PCP=2 and DEI=1.
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 is 0 if command was successful or a positive integer
upon failure.
dcb(8) dcb-app(8) dcb-apptrust(8)
Report any bugs to the Network Developers mailing list
<netdev@vger.kernel.org> where the development and maintenance is
primarily done. You do not have to be subscribed to the list to
send a message there.
Daniel Machon <daniel.machon@microchip.com>
This page is part of the iproute2 (utilities for controlling
TCP/IP networking and traffic) project. Information about the
project can be found at
⟨http://www.linuxfoundation.org/collaborate/workgroups/networking/iproute2⟩.
If you have a bug report for this manual page, send it to
netdev@vger.kernel.org, shemminger@osdl.org. This page was
obtained from the project's upstream Git repository
⟨https://git.kernel.org/pub/scm/network/iproute2/iproute2.git⟩ on
2025-08-11. (At that time, the date of the most recent commit
that was found in the repository was 2025-08-08.) If you discover
any rendering problems in this HTML version of the page, or you
believe there is a better or more up-to-date source for the page,
or you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a
mail to man-pages@man7.org
iproute2 15 may 2023 DCB-REWR(8)
Pages that refer to this page: dcb(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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