3Com 2928 User Guide - Page 216
Introduction to RSTP, Why MSTP, Weaknesses of STP and RSTP, Features of MSTP
UPC - 662705557113
View all 3Com 2928 manuals
Add to My Manuals
Save this manual to your list of manuals |
Page 216 highlights
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. z 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. z 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. Introduction to RSTP 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. z 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. z 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. Introduction to MSTP Why MSTP Weaknesses of STP and RSTP 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. Features of MSTP 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: 1-9