LAN9303 Datasheet, PDF (74/366 Pages) SMSC Corporation – Small Form Factor Three Port 10/100 Managed Ethernet Switch with Single MII/RMII/Turbo MII

6.4.4
Small Form Factor Three Port 10/100 Managed Ethernet Switch with Single MII/RMII/Turbo MII
Datasheet
VLAN Support
The Switch Engine supports 16 active VLANs out of a possible 4096. The VLAN table contains the 16
active VLAN entries, each consisting of the VID, the port membership, and un-tagging instructions.
17 16 15 14 13 12 11
...
0
Member Un-tag Member Un-tag Member Un-tag
Port 2
Port 2
Port 1
Port 1
MII
MII
VID
Figure 6.6 VLAN Table Entry Structure
On ingress, if a packet has a VLAN tag containing a valid VID (not 000h or FFFh), the VID table is
searched. If the VID is found, the VLAN is considered active and the membership and un-tag
instruction is used. If the VID is not found, the VLAN is considered foreign and the membership result
is NULL. A NULL membership will result in the packet being filtered if Enable Membership Checking
is set. A NULL membership will also result in the packet being filtered if the destination address is not
found in the ALR table (since the packet would have no destinations).
On ingress, if a packet does not have a VLAN tag or if the VLAN tag contains VID with a value of 0
(priority tag), the packet is assigned a VLAN based on the Port Default VID (PVID) and Priority. The
PVID is then used to access the above VLAN table. The usage of the PVID can be forced by setting
the 802.1Q VLAN Disable bit, in effect creating port based VLANs.
The VLAN membership of the packet is used for ingress and egress checking and for VLAN broadcast
domain containment. The un-tag instructions are used at egress on ports defined as hybrid ports.
Refer to Section 13.4.3.8, on page 280 through Section 13.4.3.11, on page 284 for detailed VLAN
register descriptions.
6.4.5 Spanning Tree Support
Hardware support for the Spanning Tree Protocol (STP) and the Rapid Spanning Tree Protocol (RSTP)
includes a per port state register as well as the override bit in the MAC Address Table entries (Section
6.4.1.5, on page 68) and the host CPU port special tagging (Section 6.4.10, on page 80).
The Switch Engine Port State Register (SWE_PORT_STATE) is used to place a port into one of the
modes as shown in Table 6.2. Normally only Port 1 and Port 2 are placed into modes other than
forwarding. Port 0, which is connected to the host CPU, should normally be left in forwarding mode.
Table 6.2 Spanning Tree States
Port State
11 - Disabled
Hardware Action
Received packets on the port are
always discarded.
Transmissions to the port are always
blocked.
Learning on the port is disabled.
Software Action
The host CPU may attempt to send packets to the
port in this state, but they will not be transmitted.
Revision 1.3 (08-27-09)
74
DATASHEET
SMSC LAN9303/LAN9303i