3com 3.01.01 Benutzerhandbuch

C

HAPTER

 8: STP O

PERATION

through the old path. If the new root port and designated port begin to forward 
data immediately after they are elected, a occasional loop may still occur. In RSTP, 
a transitional state mechanism is then adopted to ensure the new configuration 
BPDU has been propagated throughout the network before the root port and 
designated port begin to send data again. That is, the root port and designated 
port should undergo a transitional state for a period of Forward Delay before they 
enter the forwarding state. 

The Switch 8800 implements the Multiple Spanning Tree Protocol (MSTP), defined 
by IEEE 802.1s. MSTP is an enhancement to STP, and is compatible with both STP 
and RSTP, defined in IEEE 802.1w. An MSTP switch can recognize both STP and 
RSTP packets and can calculate the spanning tree with them. Beside the basic 
MSTP functions, the Switch 8800 provides additional MSTP features which include 
root bridge hold, secondary root bridge, root protection, and BPDU protection. 

STP cannot stabilize a network rapidly. Even on the point-to-point link or the edge 
port, it takes an interval as long as twice the forward delay before the network 
converges. 

MSTP makes the network converge rapidly, and distributes the traffic of different 
VLANs along their respective paths. This provides a better load-balance 
mechanism for the redundant links. 

MSTP associates VLAN with a spanning tree domain, and divides a switching 
network into several regions, each of which has a spanning tree independent of 
one another. MSTP prunes the network into a loopfree tree to avoid proliferation, 
it also provides multiple redundant paths for data forwarding to implement the 
VLAN data forwarding load-balance. 

Configuring MSTP is described in the following sections:

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MSTP Concepts are described in the following sections

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There are 4 MST regions in Figure 4.