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IXP400 Software
Access-Layer Components: Ethernet Database (IxEthDB) API
April 2005 IXP400 Software Version 2.0 Programmer’s Guide
168 Document Number: 252539, Revision: 007
An overview of the Egress tagging process is shown in Figure 55. The figure shows the decision
tree for an untagged frame. The process is identical for a tagged frame.
Table 28 presents an egress VLAN tagging/untagging behavior matrix.
Figure 55. Egress VLAN Control Path for Untagged Frames
Outgoing frame (802.1Q tagged)
Preamble Start frame Dest MAC addr Src MAC addr 0x8100 CFI VLAN ID Len Data Pad FCSPri
Outgoing frame (untagged)
Preamble Start frame Dest MAC addr Src MAC addr Len Data Pad FCS
EthAcc
Tagging override?
mbuf->ixp_ne_tx_flags.tag_over?
Tag frame with
mbuf->ixp_ne_vlan_tci
Yes
No
Tx
CFI VLAN IDPri
mbuf->ixp_ne_vlan_tci
Tag frame?
mbuf->ixp_ne_tx_flags.tag_mode?
Check port TTI table
for VLAN ID
Untag
Tag
Untag
Tag
VLAN 0 VLAN 1 VLAN 2
VLAN
4094
Tag Untag Untag Tag
EthDB
Table 28. Egress VLAN Tagging/Untagging Behavior Matrix
Tag Mode
(1)
Frame Status
(2)
Action
Untag Untagged The NPE microcode does not modify the frame.
Untag Tagged The NPE microcode removes the VLAN tag from the frame.