Cisco 15327 - Manual (Page 114)

7-8
Ethernet Card Software Feature and Configuration Guide, R7.2
Chapter 7 Configuring STP and RSTP
Spanning-Tree Address Management
Spanning-Tree Address Management
IEEE 802.1D specifies 17 multicast addresses, ranging from 0x00180C2000000 to 0x0180C2000010, to
be used by different bridge protocols. These addresses are static addresses that cannot be removed.
The ML-Series card switches supported BPDUs (0x0180C2000000 and 01000CCCCCCD) when they
are being tunneled via the protocol tunneling feature.
STP and IEEE 802.1Q Trunks
When you connect a Cisco switch to a non-Cisco device through an IEEE 802.1Q trunk, the Cisco switch
uses PVST+ to provide spanning-tree interoperability. PVST+ is automatically enabled on IEEE 802.1Q
trunks after users assign a protocol to a bridge group. The external spanning-tree behavior on access
ports and Inter-Switch Link (ISL) trunk ports is not affected by PVST+.
For more information on IEEE 802.1Q trunks, see Chapter 8, “Configuring VLANs.”
Spanning Tree and Redundant Connectivity
You can create a redundant backbone with spanning tree by connecting two switch interfaces to another
device or to two different devices. Spanning tree automatically disables one interface but enables it if
the other one fails, as shown in
Figure 7-3 . If one link is high speed and the other is low speed, the
low-speed link is always disabled. If the speeds are the same, the port priority and port ID are added
together, and spanning tree disables the link with the lowest value.
Figure 7-3 Spanning Tree and Redundant Connectivity
You can also create redundant links between switches by using EtherChannel groups. For more
information, see
Chapter 10, “Configuring Link Aggregation.”
Workstations
Active link
Blocked link
83651
ONS 15454
with ML100T-12
ONS 15454
with ML100T-12
ONS 15454
with ML100T-12