Datasheet

____________________________________________________ DS34T101, DS34T102, DS34T104, DS34T108
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10.6.1.1 VLAN Tag
As specified in IEEE Standard 802.1q, the twelve-bit VLAN identifiers enable the construction of a maximum of
4,096 distinct VLANs. For cases where this VLAN limit is inadequate VLAN stacking provides a two-level VLAN tag
structure, which extends the VLAN ID space to over 16 million VLANs. Each packet may be sent without VLAN
tags, with a single VLAN tag or with two VLAN tags (VLAN stacking).
Figure 10-11. Single VLAN Tag Format
0
01234567890
1
12345
VLAN Tag Protocol ID (TPID)
User
Priority
CFI
VLAN ID
Figure 10-12. Stacked VLAN Tag Format
The VLAN tag’s Protocol ID (TPID) can be either the typical value of 0x8100 or a value configured in the
vlan_2nd_tag_identifier fiel
d in Packet_classifier_cfg_reg7.
 The User Priority field is used to assign a priority level to the Ethernet packet.
 The CFI (Canonical Format Indicator) fields indicate the presence of a Router Information Field.
 The VLAN ID, uniquely identifies the VLAN to which the Ethernet packet belongs.
10.6.1.2 UDP/IPv4 Header
Figure 10-13. UDP/IPv4 Header Format