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RTL8305SB
2002/04/09
47
Rev.1.0
RTL8305SB will insert priority tag only from Output High Queue of Port0 (user priority field=0b111, CFI=0, VID=0x000).
If the tag removed frame is less than 64 bytes, it should add PAD with a "0x20" pattern at the packet before CRC field to fit
64-byte min packet length of IEEE 802.3 spec. The RTL8305SB will recalculate the FCS if the frame had been changed.
7.3.10 Filtering/Forwarding Reserved Control Frame
The RTL8305SB supports the ability to forward or drop the frames of the 802.1D specified reserved group MAC addresses
(control frames): 01-80-C2-00-00-03 to 01-80-C2-00-00-0F.
Address
Use
Action
01-80-C2-00-00-00
01-80-C2-00-00-01
01-80-C2-00-00-02
01-80-C2-00-00-03 to
01-80-C2-00-00-0F
Any other multicast Address
Bridge Group Address
Pause Control Frame
Reserved
Forward to all ports
Drop Frame
Drop Frame
Forward to all ports
-
Forward to all ports
Table 5: EnForward=1: same as RTL8305S
Address
Use
Action
01-80-C2-00-00-00
01-80-C2-00-00-01
01-80-C2-00-00-02
01-80-C2-00-00-03 to
01-80-C2-00-00-0F
Any other multicast Address
Bridge Group Address
Pause Control Frame
Reserved
Forward to all ports
Drop Frame
Drop Frame
Drop Frame
-
Forward to all ports
Table 6: EnForward=0
7.3.11 Broadcast Storm Control
According to the latched value of DISBRDCTRL pin upon reset, the RTL8305SB determines whether or not to proceed with
broadcast storm control. Once enabled (DISBRDCTRL=0), after consecutive 64 broadcast (DID=FFFF-FFFF-FFFF) packets
are received by one port, the incoming consecutive broadcast packets during around 800ms time window of this port will be
discarded. Any non-broadcast packet can reset the time window and broadcast counter such that the scheme restarts. It is per
port based. Note2: Trigger condition: consecutive 64 DID = FFFF-FFFF-FFFF packets. Release condition: receive
non-broadcast packet on or after 800ms.
7.3.12 Broadcast In/Out Drop
If some destination ports are blocking and the buffer is full, broadcast frames should be dropped according to configuration.
Input Drop: do not forward to any port and drop the frame directly. Output Drop: forward only to non-blocking ports
(Broadcast becomes multicast).
2. Buffer of Port4 is full, others are not full
Port 0 1 2 3 4
Rx:
Full
Input Drop: same as RTL8305S
1. Broadcast packet from Port0
Rx:
Full
Output Drop
Port 0 1 2 3 4
Figure 1: Input Drop v.s. Output Drop