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IP178C
Preliminary Data Sheet
42/91
October 27, 2005
Copyright © 2004, IC Plus Corp.
IP178C-DS-R09
2.10
Spanning tree
IP178C supports spanning tree function with the following features:
1. Detect BPDU frames by examining multicast address (01-80-c2-00-00-00).
2. Forward BPDU packets to CPU through MII and add special tag for source port information.
Forward BPDU packets from CPU according to the special tag in a frame.
Please refer to section “Tag VLAN / Tag and un-tag function”.
Port states
To support spanning tree protocol, each port of IP178C provides five port states shown in the following
table. Port 0~7 of IP178C can be configured in one of the five spanning tree states individually by
programming MII register 31.13 to enable (disable) forwarding and learning function. Port 8 (MII) is
dedicated for CPU.
State
Fwd BPDU
packet to CPU
Fwd BPDU packet
from CPU
Address
learning
Fwd all packet
normally
(Forward enable,
Learning enable)
Disable
X (note 2)
X (note 2)
X
X
(0,0)
Blocking
O
X (note 3)
X
X
(0,0)
Listening
O
O
X
X
(0,0)
Learning
O
O
O
X
(0,1)
Forwarding
O
O
O
O
(1,1)
Note1: O: enabled, X: disabled
Note2: CPU should not send packets to IP178C and should discard packets from IP178C.
Note3: CPU should not send packets to IP178C.
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