Intel IXP400 manual 10.3.5 802.1Q User Priority / QoS Support, Port ID Extraction

Intel® IXP400 Software

Access-Layer Components: Ethernet Database (IxEthDB) API

Table 28. Egress VLAN Tagging/Untagging Behavior Matrix (Continued)

Tag Mode (1)	Frame Status (2)	Action
		The NPE microcode inserts a VLAN tag into the frame. The VLAN
Tag	Untagged	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.
		The NPE microcode overwrites a VLAN TCI field of the frame with
Tag	Tagged	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.

10.3.4.7Port 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).

10.3.5802.1Q 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.

10.3.5.1Priority 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.

Programmer’s Guide	IXP400 Software Version 2.0	April 2005
	Document Number: 252539, Revision: 007	169