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IXP400 Software
Access-Layer Components: Ethernet Database (IxEthDB) API
Programmer’s Guide IXP400 Software Version 2.0 April 2005
Document Number: 252539, Revision: 007 169
10.3.4.7 Port ID Extraction
A device connected to an MII interface can be a single one-port Ethernet PHY or a multi-port
device (such as a switch). Some popular Ethernet switch chips uses the
VLAN TPID field (see
Table 26) in VLAN-tagged frames to encode the port through which a frame is received. These
devices encode the physical port from which a frame is received in the least significant 4 bits of
this field.
IxEthDB provides the API for enabling the NPE to extract this port ID information. When enabled
using the function ixEthDBVlanPortExtractionEnable(), the NPE will copy the port ID from the
VLAN type field into the
ixp_ne_src_port field of the buffer header and restore the VLAN type
field to 0x8100. This feature is disabled by default and can be switched on or off at run time.
When not enabled, the
ixp_ne_src_port value is the physical MII port ID (i.e., always 0 or 1).
10.3.5 802.1Q User Priority / QoS Support
The IxEthDB component provides support for QoS features when using NPE microcode images
that include VLAN and QoS support. This support includes:
• Priority aware transmit and receive, using different priority queues for transmit and receive.
• QoS priority (i.e., user priority, as per IEEE802.1Q) to traffic class mapping via priority
mapping tables on received frames.
• Priority frame tagging and tag removal prior to transmission. This is discussed in “Port and
VLAN-Based Egress Tagging and Tag Removal” on page 166.
10.3.5.1 Priority Aware Transmission
Submitting Ethernet frames for transmission is done by specifying a traffic class (priority) to be
used for ordering frame transmission requests. This feature is covered in Section 9.5.2.2.
Tag Untagged
The NPE microcode inserts a VLAN tag into the frame. The VLAN
tag to be inserted is created by concatenating a VLAN TPID field
(always 0x8100) with the value of the
ixp_ne_vlan_tci field from
the IX_OSAL_MBUF header.
Tag Tagged
The NPE microcode overwrites a VLAN TCI field of the frame with
the value of the
ixp_ne_vlan_tci field from the IX_OSAL_MBUF
header.
(1) - The tag mode is the result obtained by consulting the Transmit Tagging Table, unless it is overridden by
the
ixp_ne_tx_flag field of the frame’s IX_OSAL_MBUF header, as described above.
(2) - The (input) frame status is determined by examining the
ixp_ne_flags.vlan_prot flag from the frame’s
IX_OSAL_MBUF header.
Table 28. Egress VLAN Tagging/Untagging Behavior Matrix (Continued)
Tag Mode
(1)
Frame Status
(2)
Action