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The router sends hello packets at the hello time interval to the neighboring routers to make sure that
the paths are fault-free.
Max age
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The router uses the max age to determine whether a stored configuration BPDU has expired and
discards it if the max age is exceeded.
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.
A newly elected RSTP root port rapidly enters the forwarding state if the old root port on the router 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 router or a shared LAN segment) or it connects
to a point-to-point link (to another router). Edge ports directly enter the forwarding state. Connecting to
a point-to-point link, a designated port enters the forwarding state immediately after the router receives
a handshake response from the directly connected router.
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 transiting 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, so redundant links cannot be blocked based on VLAN, and
the packets of all VLANs are forwarded along the same spanning tree.
MSTP features
Developed based on IEEE 802.1s, MSTP overcomes the limitations of STP and RSTP. In addition to the
support for rapid network convergence, it allows data flows of different VLANs to be forwarded along
separate paths, providing a better load sharing mechanism for redundant links.
MSTP includes the following features:
MSTP supports mapping VLANs to spanning tree instances by means of a VLAN-to-instance
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mapping table. MSTP can reduce communication overheads and resource usage by mapping
multiple VLANs to one instance.
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MSTP divides a switched network into multiple regions, each containing multiple spanning trees
that are independent of one another.
MSTP prunes a loop network into a loop-free tree, avoiding proliferation and endless cycling of
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packets in a loop network. In addition, it provides multiple redundant paths for data forwarding,
supporting load balancing of VLAN data.
MSTP is compatible with STP and RSTP.
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