186
Network Administration: Spanning Tree and LAG
FILE LOCATION: C:\Users\gina\Desktop\Checkout_new\Dell Astute\User
Guide\Dell_Astute_Network_Admin_STP.fm
D E L L C O N F ID E N T IA L – P R E L IM I N A R Y 8 / 9 /1 6 - FO R PR O O F O N L Y
The device supports the following Spanning Tree versions:
•
Classic STP
— Provides a single path between end stations, avoiding and
eliminating loops. For more information on configuring Classic STP, see
•
Rapid STP (RSTP)
— Provides faster convergence of the spanning tree
than Classic STP. RSTP is most effective when the network topology is
naturally tree-structured, and therefore faster convergence might be
possible. RSTP is enabled by default.
Although Classic STP is guaranteed to prevent Layer 2 forwarding loops, in
a general network topology, there might be an unacceptable delay before
convergence. This means that before convergence, each bridge or switch in
the network must decide if it should actively forward traffic or not, on each
of its ports.
For more information on configuring Rapid STP, see
•
Multiple STP (MSTP)
— MSTP is based on RSTP. It detects Layer 2
loops, and attempts to mitigate them by preventing the involved port from
transmitting traffic.
Since loops exist on a per-Layer 2-domain basis, a situation occurs when a
port is blocked to eliminate a STP loop. Traffic will be forwarded to the
port that is not blocked, and no traffic will be forwarded to the port that is
blocked. This is not an efficient usage of bandwidth as the blocked port
will always be unused.
Multiple Spanning Tree Protocol (MSTP) solves this problem by enabling
several STP instances, so that it is possible to detect and mitigate loops
separately in each instance. This enables a port to be blocked for one or
more STP instances but not blocked for other STP instances. If different
VLANs are associated with different STP instances, then their traffic is
relayed based on the STP port state of their associated MST instances.
Better bandwidth utilization is resulted.
An MST region consists of adjacent MSTP bridges that have the same
VLANs to MST instances association. If there are a mixed of
STP/RSTP/MSTP bridges and/or multiple MST regions in a LAN, each
MST region in the LAN is treated as a single STP/RSTP bridge. And MST
regions are independent.
