DLPI(7P) Protocols DLPI(7P)


dlpi - Data Link Provider Interface


#include <sys/dlpi.h>


SunOS STREAMS-based device drivers wishing to support the STREAMS TCP/IP
and other STREAMS-based networking protocol suite implementations support
Version 2 of the Data Link Provider Interface (DLPI). DLPI V2 enables a
data link service user to access and use any of a variety of conforming
data link service providers without special knowledge of the provider's
protocol. Specifically, the interface is intended to support Ethernet,
X.25 LAPB, SDLC, ISDN LAPD, CSMA/CD, FDDI, token ring, token bus, Bisync,
and other datalink-level protocols.

The interface specifies access to the data link service provider in the
form of M_PROTO and M_PCPROTO type STREAMS messages and does not define a
specific protocol implementation. The interface defines the syntax and
semantics of primitives exchanged between the data link user and the data
link provider to attach a physical device with physical-level address to
a stream, bind a datalink-level address to the stream, get
implementation-specific information from the data link provider, exchange
data with a peer data link user in one of three communication modes
(connection, connectionless, acknowledged connectionless), enable/disable
multicast group and promiscuous mode reception of datalink frames, get
and set the physical address associated with a stream, and several other

Solaris conforms to The Open Group Technical Standard for DLPI, Version
2. For free access to this specification, point your browser to
www.opengroup.org/pubs/catalog/c811.htm. Solaris also provides extensions
to the DLPI standard, as detailed in this man page.

Notification Support

Enables DLPI consumers to register for notification when events of
interest occur at the DLPI provider. The negotiation can be performed
on any attached DLPI stream, and begins with the DLPI consumer,
sending a DL_NOTIFY_REQ to the provider, which is an M_PROTO message
with the following payload:

typedef struct {
t_uscalar_t dl_primitive;
uint32_t dl_notifications;
uint32_t dl_timelimit;
} dl_notify_req_t;

The dl_primitive field must be set to DL_NOTIFY_REQ; the dl_timelimit
field is reserved for future use and must be set to zero. The
dl_notifications field is a bitmask containing the event types the
consumer is interested in receiving, and must be zero or more of:

DL_NOTE_LINK_DOWN Notify when link has gone down
DL_NOTE_LINK_UP Notify when link has come up
DL_NOTE_PHYS_ADDR Notify when address changes
DL_NOTE_SDU_SIZE Notify when MTU changes
DL_NOTE_SPEED Notify when speed changes

Consumers might find it useful to send a DL_NOTIFY_REQ message with
no requested types to check if the DLPI provider supports the

Upon receiving the DL_NOTIFY_REQ, the DLPI provider must generate a
DL_NOTIFY_ACK, which is an M_PROTO message with the following

typedef struct {
t_uscalar_t dl_primitive;
uint32_t dl_notifications;
} dl_notify_ack_t;

The dl_primitive field must be set to DL_NOTIFY_ACK. The
dl_notifications field must include any notifications that the
provider supports, along with any other unrequested notifications
that the provider supports. However, regardless of the notifications
the provider supports, it is restricted to sending only DL_NOTIFY_IND
messages (see below) that were requested in the DL_NOTIFY_REQ.

Since there are additional notification types which are not yet
available for public use, DLPI consumers and providers must take care
when inspecting and setting the dl_notifications field. Specifically,
consumers must be careful to only request the above notification
types, and providers must be careful to not include any unrecognized
notification types in the dl_notifications field when constructing
the DL_NOTIFY_ACK. In addition, DL_NOTIFY_IND's that are received
with undocumented dl_notification or dl_data values must be ignored.

DLPI consumers might receive a DL_ERROR_ACK message (with
dl_error_primitive set to DL_NOTIFY_REQ) in response to the initial
DL_NOTIFY_REQ message. This message indicates that the DLPI provider
does not support the DLPI notification extension. Otherwise, the DLPI
consumer receives a DL_NOTIFY_ACK and should expect to receive
DL_NOTIFY_IND messages for any types that it requested that were
still set in it. The DL_NOTIFY_IND is an M_PROTO message with the
following payload:

typedef struct {
t_uscalar_t dl_primitive;
uint32_t dl_notification;
uint32_t dl_data;
t_uscalar_t dl_addr_length;
t_uscalar_t dl_addr_offset;
} dl_notify_ind_t;

The dl_primitive field must be set to DL_NOTIFY_IND, and the
dl_notification field must be set to the event type that has occurred
(for example, DL_NOTE_LINK_DOWN). Only a single event type can be set
in each DL_NOTIFY_IND.

For the DL_NOTE_SPEED event type, dl_data must be set to the current
interface speed in kilobits per second. For the DL_NOTE_PHYS_ADDR
event type, dl_data must be set to DL_CURR_PHYS_ADDR. For the
DL_NOTE_SDU_SIZE event type, dl_data must be set to the current MTU
in bytes. Otherwise, dl_data must be set to zero.

For the DL_NOTE_PHYS_ADDR event type, the dl_addr_length field must
be set to the length of the address, and the dl_addr_offset field
must be set to offset of the first byte of the address, relative to
b_rptr (for example, if the address immediately follows the
dl_notify_ind structure, dl_addr_offset is set to 'sizeof
(dl_notify_ind)'). For all other event types, the dl_addr_length and
dl_addr_offset fields must be set to zero by DLPI providers and
ignored by DLPI consumers.

In addition to generating DL_NOTIFY_IND messages when a requested
event has occurred, the DLPI provider must initially generate one or
more DL_NOTIFY_IND messages to notify the DLPI consumer of the
current state of the interface. For instance, if the consumer has
requested DL_NOTE_LINK_UP | DL_NOTE_LINK_DOWN, the provider must send
a DL_NOTIFY_IND containing the current state of the link (either
DL_NOTE_LINK_UP or DL_NOTE_LINK_DOWN) after sending the

For the initial DL_NOTIFY_IND message, the DLPI provider is strongly
recommended against sending DL_NOTE_LINK_DOWN, even if the interface
is still initializing and is not yet ready to send or receive
packets. Instead, either delaying the DL_NOTIFY_IND message until the
interface is ready or optimistically reporting DL_NOTIFY_LINK_UP and
subsequently reporting DL_NOTE_LINK_DOWN if the negotiation fails
is strongly preferred. This prevents DL_NOTIFY_IND consumers from
needlessly triggering network failover operations and logging error
messages during network interface initialization.

The DLPI provider must continue to generate DL_NOTIFY_IND messages
until it receives a new DL_NOTIFY_REQ message or the DLPI stream is
detached (or closed). Further, a DLPI style 2 provider must keep
track of the requested events after a DL_DETACH_REQ operation, and if
a subsequent DL_ATTACH_REQ is received, it must send gratuitous
DL_NOTIFY_IND messages to notify the consumer of the current state
of the device, since the state might have changed while detached
(or the consumer might have simply discarded its previous state).

Passive Consumers of Aggregated Links

Solaris link aggregations as configured by dladm(1M) export DLPI
nodes for both the link aggregation, and individual links that
comprises the aggregation, to allow observability of the aggregated
links. To allow applications such as snoop(1M) to open those
individual aggregated links while disallowing other consumers such as
ip(7P), DL_PASSIVE_REQ (a DLPI primitive), must be issued by
snoop(1M) and similar applications.

The DL_PASSIVE_REQ primitive is an M_PROTO message containing the
following payload:

typedef struct {
t_uscalar_t dl_primitive;
} dl_passive_req_t;

Issuing this primitive allows the consumer of a DLPI link to coexist
with a link aggregation that also uses the link. Such a consumer is
considered passive.

Consumers that don't use this primitive while an aggregation is using
the link receive DL_SYSERR/EBUSY when issuing the following DLPI


A consumer that has not issued a DL_PASSIVE_REQ and has successfully
issued one of the above primitives is considered active.

The creation of a link aggregation using dladm(1M) fails if one of
the links included in the aggregation has an active consumer, but
succeeds if the links do not have any DLPI consumers or only passive

Raw Mode

The DLIOCRAW ioctl function is used by some DLPI applications, most
notably the snoop(1M) command. The DLIOCRAW command puts the stream
into a raw mode, which, upon receive, causes the full MAC-level
packet to be sent upstream in an M_DATA message instead of it being
transformed into the DL_UNITDATA_IND form normally used for reporting
incoming packets. Packet SAP filtering is still performed on streams
that are in raw mode. If a stream user wants to receive all incoming
packets it must also select the appropriate promiscuous modes. After
successfully selecting raw mode, the application is also allowed to
send fully formatted packets to the provider as M_DATA messages for
transmission. DLIOCRAW takes no arguments. Once enabled, the stream
remains in this mode until closed.

Native Mode

Some DLPI providers are able to represent their link layer using more
than one link-layer format. In this case, the default link-layer
format can minimize impact to applications, but might not allow truly
native link-layer headers to be sent or received. DLPI consumers who
wish to use the native link-layer format can use DLIOCNATIVE to
transition the stream. DLIOCNATIVE takes no arguments and returns the
DLPI mac type associated with the new link-layer format upon
success. Once enabled, the stream remains in this mode until closed.
Note that DLIOCNATIVE does not enable transition between dissimilar
DLPI mac types and (aside from the link-layer format), the new DLPI
mac type is guaranteed to be semantically identical. In particular,
the SAP space and addressing format are not affected and the effect
of DLIOCNATIVE is only visible when in raw mode, though any
subsequent DL_INFO_REQ requests generate responses with dl_mac_type
set to the native DLPI type.


While a DLPI provider provides its maximum SDU via dl_max_sdu in
DL_INFO_ACK messages, this value typically represents a standard
maximum SDU for the provider's media (1500 for Ethernet for example),
and not necessarily the absolute maximum amount of data that the
provider is able to transmit in a given data unit. The margin "is
the extra amount of data in bytes that the provider can transmit
beyond its advertised maximum SDU. For example, if a DL_ETHER
provider can handle packets whose payload section is no greater than
1522 bytes and its dl_max_sdu is set to 1500 (as is typical for
Ethernet), then the margin would be 22. If a provider supports a non-
zero margin, it implements the DLIOCMARGININFO ioctl, whose data is a
t_uscalar_t representing the margin size.


VLAN Support

Traditional VLAN Access

Some DL_ETHER DLPI providers support IEEE 802.1Q Virtual LANs (VLAN). For
these providers, traffic for a particular VLAN can be accessed by opening
a VLAN data-link.

Unless raw mode is enabled, a DLPI stream bound to a VLAN data-link
behaves no differently than a traditional DLPI stream. As with non-VLAN
data-link access, data must be sent to a DLPI provider without link-
layer headers (which are added by the provider) and received data is
passed to interested DLPI consumers without link-layer headers. As a
result, DLPI consumers not require special-case logic to implement VLAN

SAP-Based VLAN Access
As per IEEE 802.1Q, all VLAN traffic is sent using Ether- Type 0x8100,
meaning that in addition to directly opening a VLAN data-link, all VLAN
traffic for a given underline data-link can also be accessed by opening
the underlying data-link and binding to SAP 0x8100. Accordingly, all VLAN
traffic (regardless of VLAN ID) can be sent and received by the DLPI
consumer. However, even when raw mode is disabled, packets are received
starting with their VLAN headers and must be sent to the DLPI provider
with their VLAN headers already pre-pended (but without Ethernet
headers). Because adhering to these semantics requires each DLPI
consumer to have specialized knowledge of VLANs, VLANs should only be
accessed in this way when the traditional VLAN access method is
insufficient (for example, because access to all VLAN traffic, regardless
of VLAN ID, is needed).

Because all VLAN traffic is sent with SAP 0x8100, VLAN traffic not
filtered at the physical (DL_PROMISC_PHYS) level is also visible if a
DLPI consumer enables promiscuous mode of a stream at the DL_PROMISC_SAP
level. As mentioned earlier, these packets are received starting with
their VLAN headers if raw mode is not enabled.

QoS Support

The IEEE 802.1Q standard defines eight classes of priority values used by
QoS traffic control of Ethernet packets. Although the priority values are
encoded in the 802.1Q tags, they can be used independently from VLANs.
In particular, a special priority tagged packet (with VLAN ID zero but
priority bits non-zero) does not belong to any VLAN.

The priority value can be set on either a per-stream or per-packet basis.
DLPI consumers can specify the per-stream priority using the
DL_UDQOS_REQ request (the priority value remains unchanged until the next
DL_UDQOS_REQ) and also specify the per-packet priority value using the
b_band field of a M_DATA message or the dl_priority field of a

Raw Mode

SAP-Based VLAN Access
When raw mode is enabled, the complete, unmodified MAC- level packet
(including Ethernet and VLAN headers) is passed to interested DLPI
consumers. Similarly, the entire MAC-level packet (including Ethernet and
VLAN headers) must be sent to the DLPI provider for transmission. Note
that the priority value specified in the b_band field can be overridden
by encoding the priority value (if any) into the VLAN header.

Traditional VLAN Access

When raw mode is enabled, only packets with the correct VLAN ID are
passed up to interested DLPI consumers. With the exception of priority-
tagged packets, DLPI providers must strip off the VLAN headers (while
retaining the preceding Ethernet headers) before sending up the packets.
For priority-tagged packets, DLPI providers must use the reserved tag 0
to encode the VLAN TCI and send up the packets.

On the transmit-side, DLPI consumers must send the packets down to the
DLPI providers without the VLAN headers (but with the Ethernet headers)
unless certain QoS support is required. If QoS support is needed, the
packet can have the VLAN header to indicate the priority value, however
its VLAN ID must be zero. The DLPI providers then insert the VLAN tags or
encode the VLAN tags using the priority value specified in the VLAN
headers and send the packets.


Files in or under /dev.


See attributes(5) for descriptions of the following attributes:

|Interface Stability (Notification support/Passive mode behavior) | Committed |


dladm(1M), snoop(1M), libdlpi(3LIB), gld(7D), ip(7P)


A Solaris DLPI link name consists of a DLPI provider name followed by a
numeric PPA (physical point of attachment).

The DLPI provider name must be between 1 and 16 characters in length,
though names between 3 and 8 characters are preferred. The DLPI provider
name can consist of any alphanumeric character (a-z, A-Z, 0-9), and the
underscore (_). The first and last character of the DLPI provider name
cannot be a digit.

The PPA must be a number between 0 and 4294967294 inclusive. Leading
zeroes are not permitted.

April 9, 2016 DLPI(7P)