Stp and rstp overview – Allied Telesis AT-S60 User Manual
Page 229
AT-S60 Management Software User’s Guide
Section II: Advanced Features
229
STP and RSTP Overview
A physical loop in a network topology can pose a significant problem to
Ethernet network performance. A loop exists when two or more nodes
on a network can transmit data to each other over more than one data
link. The problem with physical loops is that data packets can become
caught in repeating cycles, referred to as broadcast storms, that
needlessly consume network bandwidth and significantly reduce
network performance.
STP and RSTP prevent data loops from forming by ensuring that only
one path exists between the end nodes in your network. Should one of
the protocols detect multiple paths, it places the extra paths in a standby
or blocking mode, leaving only one main active path.
STP and RSTP can also activate a redundant path if the main path goes
down. So not only do these protocols guard against multiple links
between segments and the risk of broadcast storms, but they can also
maintain network connectivity by activating a backup redundant path in
case a main link fails.
The principal difference between the two protocols is in the time each
takes to complete the process commonly referred to as convergence.
When a change is made to the network topology, such as the addition of
a new bridge, a spanning tree protocol must determine whether there
are redundant paths that must be blocked to prevent data loops, or
activated to maintain intercommunications between the various
network segments. This is the process of convergence.
With STP, convergence can take minutes to complete in a large network.
This can result in lost data packets and the loss of intercommunication
between various parts of the network during the convergence process.
RSTP is much faster. It can complete a convergence in seconds, and so
diminish the possible impact the process can have on your network.
The STP implementation on the AT-8400 Series switch complies with the
IEEE 802.1d standard. The RSTP implementation complies with the IEEE
802.1w standard. The following subsections provide a basic overview on
how STP and RSTP operate and define the different parameters that you
can adjust.
❑ Bridge Priority and the Root Bridge on page 230