Mstp Configuration; Why Stp; Protocol Packets Of Stp - HP 5820X series Configuration Manual

MSTP configuration

As a Layer 2 management protocol, the STP eliminates Layer 2 loops by selectively blocking redundant
links in a network, and in the mean time, allows for link redundancy.
Like many other protocols, STP evolves as the network grows. The later versions of STP are the RSTP and
the MSTP. This chapter describes the features of STP, RSTP, and MSTP.

Why STP

STP was developed based on the 802.1d standard of IEEE to eliminate loops at the data link layer in a
LAN. Devices running this protocol detect loops in the network by exchanging information with one
another and eliminate loops by selectively blocking certain ports to prune the loop structure into a loop-
free tree structure. This avoids proliferation and infinite cycling of packets that would occur in a loop
network and prevents decreased performance of network devices caused by duplicate packets received.
In the narrow sense, STP refers to IEEE 802.1d STP. In the broad sense, STP refers to the IEEE 802.1d STP
and various enhanced spanning tree protocols derived from that protocol.

Protocol packets of STP

STP uses BPDUs, also known as "configuration messages," as its protocol packets.
STP-enabled network devices exchange BPDUs to establish a spanning tree. BPDUs contain sufficient
information for the network devices to complete spanning tree calculation.
In STP, BPDUs have the following types:
Configuration BPDUs, used for calculating a spanning tree and maintaining the spanning tree
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topology.
TCN BPDUs, used for notifying the concerned devices of network topology changes, if any.
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Configuration BPDUs contain sufficient information for the network devices to complete spanning tree
calculation. Important fields in a configuration BPDU include:
Root bridge ID: consisting of the priority and MAC address of the root bridge.
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Root path cost: the cost of the path to the root bridge denoted by the root identifier from the
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transmitting bridge.
Designated bridge ID: consisting of the priority and MAC address of the designated bridge.
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Designated port ID: consisting of the priority and global port number of the designated port.
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Message age: age of the configuration BPDU while it propagates in the network.
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Max age: maximum age of the configuration BPDU stored on the switch.
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Hello time: configuration BPDU transmission interval.
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Forward delay: the delay used by STP bridges to transition port state.
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