Figure 23-17 Stp Blocked Path; Figure 23-18 Spanning Tree Map On Circuit Window - Cisco ONS 15454 SDH Configuration Manual

Chapter 23 E-Series and G-Series Ethernet Operation
STP operates over all packet-switched ports including Ethernet and OC-N/STM-N ports. On Ethernet
ports, STP is enabled by default but can be disabled. A user can also disable or enable STP on a
circuit-by-circuit basis on Ethernet cards configured as single-card EtherSwitch (unstitched) in a
point-to-point configuration. However, turning off STP protection on a circuit-by-circuit basis means
that the SONET/SDH system is not protecting the Ethernet traffic on this circuit, and the Ethernet traffic
must be protected by another mechanism in the Ethernet network. On OC-N/STM-N interface ports, the
ONS node activates STP by default, and STP cannot be disabled.
The Ethernet card can enable STP on the Ethernet ports to create redundant paths to the attached Ethernet
equipment. STP connects cards so that both equipment and facilities are protected against failure.
STP detects and eliminates network loops. When STP detects multiple paths between any two network
hosts, STP blocks ports until only one path exists between any two network hosts
single path eliminates possible bridge loops. This is crucial for shared packet rings, which naturally
include a loop.
Figure 23-17
To remove loops, STP defines a tree that spans all the switches in an extended network. STP forces
certain redundant data paths into a standby (blocked) state. If one network segment in the STP becomes
unreachable, the STP algorithm reconfigures the STP topology and reactivates the blocked path to
reestablish the link. STP operation is transparent to end stations, which do not discriminate between
connections to a single LAN segment or to a switched LAN with multiple segments. The ONS node
supports one STP instance per circuit and a maximum of eight STP instances per ONS node.
The Circuit window shows forwarding spans and blocked spans on the spanning tree map
Figure 23-18
Green represents forwarding spans and purple represents blocked (protect) spans. If you have a packet
Note
ring configuration, at least one span should be purple.
STP Blocked Path
Primary path (forwarding)
Redundant path (blocked)
Spanning Tree Map on Circuit Window
Cisco ONS 15454 and Cisco ONS 15454 SDH Ethernet Card Software Feature and Configuration Guide, R8.0
E-Series Spanning Tree (IEEE 802.1D)
(Figure 23-17). The
(Figure 23-18).
23-21