3com 2928 Betriebsanweisung

 

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For this reason, as a mechanism for state transition in STP, the newly elected root ports or designated 
ports require twice the forward delay time before transiting to the forwarding state to ensure that the new 
configuration BPDU has propagated throughout the network.  

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Hello time is the time interval at which a device sends hello packets to the surrounding devices to 
ensure that the paths are fault-free.  

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Max age is a parameter used to determine whether a configuration BPDU held by the device has 
expired. A configuration BPDU beyond the max age will be discarded.  

Developed based on the 802.1w standard of IEEE, RSTP is an optimized version of STP. It achieves 
rapid network convergence by allowing a newly elected root port or designated port to enter the 
forwarding state much quicker under certain conditions than in STP. 

 

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In RSTP, a newly elected root port can enter the forwarding state rapidly if this condition is met: The 
old root port on the device has stopped forwarding data and the upstream designated port has 
started forwarding data.  

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In RSTP, a newly elected designated port can enter the forwarding state rapidly if this condition is 
met: The designated port is an edge port or a port connected with a point-to-point link. If the 
designated port is an edge port, it can enter the forwarding state directly; if the designated port is 
connected with a point-to-point link, it can enter the forwarding state immediately after the device 
undergoes handshake with the downstream device and gets a response.  

 

STP does not support rapid state transition of ports. A newly elected root port or designated port must 
wait twice the forward delay time before transiting to the forwarding state, even if it is a port on a 
point-to-point link or an edge port, which directly connects to a user terminal rather than to another 
device or a shared LAN segment.  

Although RSTP supports rapid network convergence, it has the same drawback as STP does: All 
bridges within a LAN share the same spanning tree, so redundant links cannot be blocked based on 
VLAN, and the packets of all VLANs are forwarded along the same spanning tree.  

Developed based on the 802.1s standard of IEEE, MSTP overcomes the shortcomings of STP and 
RSTP. In addition to the support for rapid network convergence, it also allows data flows of different 
VLANs to be forwarded along separate paths, thus providing a better load sharing mechanism for 
redundant links.  

MSTP features the following: