802.1Q tag mode link property
Release binding: Patch
Interface Stability: Committed
Related Case: PSARC 2006/358 VLAN Observability Enhancement
Summary
-------
This case introduces a GLDv3 link property named "tagmode" to
control the conditions in which the kernel inserts VLAN tags in
outgoing packets.
Background
----------
The comprehensive VLAN tagging changes made by PSARC 2006/358 also
fixed a bug that prevented Solaris from inserting a user priority
tag (VLAN tag with NULL VLAN ID bug non-zero priority) when the
sender specifies a priority for an outgoing packet over a physical
Ethernet link. This bug was:
6434130 i_dls_ether_header() doesn't generate VLAN header when
priority is non-zero
As a result of this bug fix, when an application requests a user
priority (either by using the DL_UDQOS_REQ DLPI primitive, by
setting the dl_priority field of a DL_UNITDATA_REQ message, or by
setting b_band on an M_DATA message) when sending a packet on a
physical Ethernet link, the kernel will insert a VLAN header with a
NULL VLAN ID and a priority as specified by the user.
This new behavior is in-line with the 802.1Q IEEE specification.
Bridges receiving such packets should recognize these as
user-priority tagged packets and process the priority setting
accordingly.
Unfortunately, experience with this fix has uncovered that a number
of widely used bridges (switches) don't handle these special
user-priority tagged packets and simply drop them. This problem is
documented in detail in the following CR:
6797256 GLD interfaces unexpectedly send VLAN tagged packets
This issue, in combination with the fact that some widely deployed
applications unconditionally request priority processing on all of
their outgoing packets, means that these applications no longer work
at all over physical Ethernet links connected to these problematic
switches.
Solution
--------
This case introduces a link property (see dladm(1M)) named "tagmode"
that controls the conditions in which the kernel will insert VLAN
tags on packets being transmitted on the link. Two mode values can
be assigned to this property:
normal Insert a VLAN tag to outgoing packets as needed
whenever requested. This includes two cases:
1. The packet belongs to a VLAN.
2. The user requested priority tagging.
vlanonly Only insert a VLAN tag when the outgoing packet
belongs to a VLAN. If a tag is being inserted in this
mode and the user has also requested a non-zero
priority, the priority is honored and included in the
VLAN tag.
Only DL_ETHER links will support this property, and its default
value will be "vlanonly". Setting the property to "normal"
demonstrates deliberate understanding that the feature is functional
on the associated datalink.
Impact On IFF_COS_ENABLED Flag
------------------------------
The IFF_COS_ENABLED flag documented as "Cos" in ifconfig(1M)
reflects whether or not an interface supports a class of service
marking (with 802.1D user priority marking being one example). This
flag is currently set on all GLDv3 datalinks regardless of their
ability to honor user priorities.
One consumer of this flag is the IPQos functionality, which can be
configured to request per-packet user priorities over CoS-capable
interfaces (see ipqos(7ipp) and ipqosconf(1M)). It does this on IP
interfaces that have the IFF_COS_ENABLED flag set.
In order to accurately reflect the link's abilities to use
priorities, this case changes the system such that the
IFF_COS_ENABLED flag will only be set on VLAN links and on physical
links that have their "tagmode" properties set to "normal". This
will ensure that IPQos and other consumers of the IFF_COS_ENABLED
flag do not erroneously request priorities over links that don't
support them or have been explicitly configured to not use them.
Change of System Default Behavior
---------------------------------
The choice of "vlanonly" as the default value for the "tagmode" link
property constitutes a change in behavior from how the system
behaved after the fix to 6434130 was integrated. As previously
mentioned, the fix to 6434130 caused the system to always insert a
user-priority tag when requested. It will now only do so if the
administrator explicitly changes the "tagmode" property to have the
value "normal".
The fix to 6434130 was included with s10u7, and prior to that, most
drivers (including all GLDv2 and GLDv3 drivers) failed to insert
user-priority tags. Since 6434130 has no external customer records,
one can thus assume that no-one noticed that this was broken, and so
reverting the system default behavior back to its prior state will
not be disruptive.
The dladm(1M) man page will be updated to document the "tagmode"
link property, and the "CoS" section of the ifconfig(1M) man page
will be modified to describe how to enable "CoS" using the "tagmode"
property.
