diff options
Diffstat (limited to 'Documentation/networking/dsa')
-rw-r--r-- | Documentation/networking/dsa/configuration.rst | 68 |
1 files changed, 68 insertions, 0 deletions
diff --git a/Documentation/networking/dsa/configuration.rst b/Documentation/networking/dsa/configuration.rst index 774f0e76c746..2b08f1a772d3 100644 --- a/Documentation/networking/dsa/configuration.rst +++ b/Documentation/networking/dsa/configuration.rst @@ -292,3 +292,71 @@ configuration. # bring up the bridge devices ip link set br0 up + +Forwarding database (FDB) management +------------------------------------ + +The existing DSA switches do not have the necessary hardware support to keep +the software FDB of the bridge in sync with the hardware tables, so the two +tables are managed separately (``bridge fdb show`` queries both, and depending +on whether the ``self`` or ``master`` flags are being used, a ``bridge fdb +add`` or ``bridge fdb del`` command acts upon entries from one or both tables). + +Up until kernel v4.14, DSA only supported user space management of bridge FDB +entries using the bridge bypass operations (which do not update the software +FDB, just the hardware one) using the ``self`` flag (which is optional and can +be omitted). + + .. code-block:: sh + + bridge fdb add dev swp0 00:01:02:03:04:05 self static + # or shorthand + bridge fdb add dev swp0 00:01:02:03:04:05 static + +Due to a bug, the bridge bypass FDB implementation provided by DSA did not +distinguish between ``static`` and ``local`` FDB entries (``static`` are meant +to be forwarded, while ``local`` are meant to be locally terminated, i.e. sent +to the host port). Instead, all FDB entries with the ``self`` flag (implicit or +explicit) are treated by DSA as ``static`` even if they are ``local``. + + .. code-block:: sh + + # This command: + bridge fdb add dev swp0 00:01:02:03:04:05 static + # behaves the same for DSA as this command: + bridge fdb add dev swp0 00:01:02:03:04:05 local + # or shorthand, because the 'local' flag is implicit if 'static' is not + # specified, it also behaves the same as: + bridge fdb add dev swp0 00:01:02:03:04:05 + +The last command is an incorrect way of adding a static bridge FDB entry to a +DSA switch using the bridge bypass operations, and works by mistake. Other +drivers will treat an FDB entry added by the same command as ``local`` and as +such, will not forward it, as opposed to DSA. + +Between kernel v4.14 and v5.14, DSA has supported in parallel two modes of +adding a bridge FDB entry to the switch: the bridge bypass discussed above, as +well as a new mode using the ``master`` flag which installs FDB entries in the +software bridge too. + + .. code-block:: sh + + bridge fdb add dev swp0 00:01:02:03:04:05 master static + +Since kernel v5.14, DSA has gained stronger integration with the bridge's +software FDB, and the support for its bridge bypass FDB implementation (using +the ``self`` flag) has been removed. This results in the following changes: + + .. code-block:: sh + + # This is the only valid way of adding an FDB entry that is supported, + # compatible with v4.14 kernels and later: + bridge fdb add dev swp0 00:01:02:03:04:05 master static + # This command is no longer buggy and the entry is properly treated as + # 'local' instead of being forwarded: + bridge fdb add dev swp0 00:01:02:03:04:05 + # This command no longer installs a static FDB entry to hardware: + bridge fdb add dev swp0 00:01:02:03:04:05 static + +Script writers are therefore encouraged to use the ``master static`` set of +flags when working with bridge FDB entries on DSA switch interfaces. |