Figure 4 Multiple Spanning Tree Groups - Nortel 8300 User Manual

Figure 4
Multiple spanning tree groups
Spanning Tree Protocol controls
The ports associated with a VLAN and VLANs themselves must be
contained within a single STG to prevents problems with spanning tree
blocking ports and loss of connectivity within the VLAN.
Each untagged port can belong only one STG, while tagged ports can
belong to more than one STG. When a tagged port belongs to more than
one STG, the spanning tree bridge protocol data units (BPDUs) are tagged
to distinguish those of one STG from those of another STG. BPDUs from
STG 1 are not tagged. The tagged BPDUs are transmitted using a multicast
MAC address as tagged frames with a VLAN ID. Because tagged BPDUs
are not part of the IEEE 802.1D standard, not all devices can interpret
tagged BPDUs.
You can enable or disable the Spanning Tree Protocol at the port or at the
spanning tree group level. If you disable the protocol at the group level,
received BPDUs are handled like a MAC-level multicast and flooded out the
other ports of the STG. Note that an STG can contain one or more VLANs.
Remember that MAC broadcasts are flooded out on all ports of a VLAN; a
BPDU is a MAC-level message, but the BPDU is flooded out all ports on
the STG, which can encompass many VLANs.
When STP is globally enabled on the STG, BPDU handling depends on
the STP setting of the port:
•
•
Configuration — VLANs, Spanning Tree, and Static Link Aggregation using Device Manager
Copyright © 2005-2007, Nortel Networks
.
When STP is enabled on the port, received BPDUs are processed in
accordance with STP.
When STP is disabled on the port, the port stays in a forwarding state,
received BPDUs are dropped and not processed, and no BPDU is
generated.
Nortel Ethernet Routing Switch 8300
NN46200-510 03.01 Standard
4.0 27 August 2007
Spanning Tree Protocol (STP) 27