Rapid Spanning Tree Protocol (RSTP)
Rapid Spanning Tree Protocol (RSTP)
When a connection between Ethernet switches exists, making a second connection
directly or indirectly (through a third switch) will disrupt the Ethernet network unless the
Rapid Spanning Tree Protocol (RSTP) is active. The RSTP will disable all redundant paths,
and transmit data only over the preferred path; if the preferred path fails, the next port on
the priority list will become enabled. When the OM1004 is in RSTP mode, and Hardware
(default) mode, and has redundant paths, the data path with the lowest cost (highest
throughput) becomes active, and the other path(s) are blocked. When alternate paths have
the same cost, the lowest number port (including the RJ45 port) is the preferred path.
Alternately the serial Configuration Port on the OM1004 can be used to set the priority of
the ports (SW2 up), however this is best avoided unless the user is familiar with RSTP.
The following figure shows an an example of an acceptable OM1004 spanning tree
configuration when in the default plug-and-play mode. Note that each port connects to
one other spanning tree port.
The following figure shows an unacceptable spanning tree configuration when in the
default plug-and-play mode. Note that port 2 of switch A connects to switch B and C.
If it is desired to use the above topology, the OM1004 should be set for software
configuration, and configuration menu item
e Set port admin p2p MAC
should be set to
NO (the default of AUTO usually becomes YES). This will allow the above topology at the
expense of a longer recovery time when the topology changes.
3
1
2
3
1
2
3
1
2
3
A
B
C
No Spanning Tree
1
2
3
1
2
3
1
2
3
1
2
3
4
5
6
D
A
B
C