Zte ZXR10 5900E Series User Manual page 49

Note:
Bridges in an MST area mush have same MST config ID. Two
bridges with same MST config ID are probably in different MST
area. For example, if two bridges with the same MST config
ID are connected through the LAN of another MST area, they
should belong to different MST area.
MST area may have different spanning tree structures: Inter-
nal Spanning Tree (IST), MST1, MST2 and MSTn. Each MSTi
can be regarded as an MSTI. The bridge forwards the frame
with the designated VID based on the path to which the VID
corresponds. The mapping between VID and MSTI is shown
by the MST Config ID. The spanning tree structure of MSTI is
decided by priority parameters configured by the system.
3. MST Instance
MST bridge must support two kinds of instances that is IST
instance and multiple MST instances. By default, IST runs in
an area. All the VLANs are configured to the IST by default.
IST connects all the switches in the area. IST is responsible
for communication with other MST areas and SST areas out-
side the area. MST instance does not send the BPDU packet
independently. Spanning tree information is included in the
M-record, and transmitted as part of the IST BPDU inside the
area.
4. CIST
internal IST and external
stitute Common and Internal Spanning Tree (CIST). It means
that CIST is same as IST inside the MST area, and CST outside
the MST area.
5. IST Region Root
Each MST area has an IST Region Root switch which has min-
imum overhead from the CST Root path. When CIST Root is
in a certain MST area, the CIST Root is the IST Region Root
of this MST area. After the IST Region Root is selected, other
ports towards the CIST Root in the area will be blocked.
6. MST BPDU
MSTI inside the MST area does not communicate with the out-
side, while the IST exchanges
Inside the area MSTI does not send BPDU packets indepen-
dently. MST BPDU packets are sent by the IST includes MSTI
information. MSTI uses a flag to show there is need to send
the MST BPDU packet. IST is responsible for sending packets.
All MSTIs that need to send BPDU packets place their informa-
tion in the M-record structure which is sent as part of the IST
BPDU.
Confidential and Proprietary Information of ZTE CORPORATION
Chapter 5 STP Configuration
CST of each MST area jointly con-
BPDU packets with the outside.
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