Rstp; Mstp; Stp And Rstp Limitations; Mstp Features - HP 6600 Configuration Manual

RSTP

RSTP achieves rapid network convergence by allowing a newly elected root port or designated port to
enter the forwarding state much faster than STP.
A newly elected RSTP root port rapidly enters the forwarding state if the old root port on the device has
stopped forwarding data and the upstream designated port has started forwarding data.
A newly elected RSTP designated port rapidly enters the forwarding state if it is an edge port (which
directly connects to a user terminal rather than to another network device or a shared LAN segment), or
it connects to a point-to-point link (to another device). Edge ports directly enter the forwarding state.
When connecting to a point-to-point link, a designated port enters the forwarding state immediately after
the device receives a handshake response from the directly connected device.

MSTP

STP and RSTP limitations

STP does not support rapid state transition of ports. A newly elected port must wait twice the forward
delay time before it transits to the forwarding state, even if it connects to a point-to-point link or is an edge
port.
Although RSTP supports rapid network convergence, it has the same drawback as STP. All bridges within
a LAN share the same spanning tree, and packets from all VLANs are forwarded along the same
spanning tree, so redundant links cannot be blocked based on VLAN, and load sharing among VLANs
cannot be implemented.

MSTP features

Developed based on IEEE 802.1s, MSTP overcomes the limitations of STP and RSTP. In addition to
supporting rapid network convergence, it also provides a better load sharing mechanism for redundant
links by allowing data flows from different VLANs to be forwarded along separate paths.
MSTP provides the following features:
Divides a switched network into multiple regions, each of which contains multiple spanning trees
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that are independent of one another.
Supports mapping VLANs to spanning tree instances by means of a VLAN-to-instance mapping
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table. MSTP can reduce communication overheads and resource usage by mapping multiple
VLANs to one instance.
Prunes a looped network into a loop-free tree, which avoids proliferation and endless cycling of
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packets. In addition, it supports load balancing of VLAN data by providing multiple redundant
paths for data forwarding.
Compatible with STP and RSTP.
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MSTP basic concepts

Figure 16 shows a switched network that comprises four MST regions, with each MST region comprising
four MSTP devices. Figure 17 shows the network topology of MST region 3.
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