Spanning Tree Modes; Spanning Tree Faststart; Understanding Stgs And Vlans - Nortel 8300 User Manual

28 VLANs, Spanning Tree, and Static Link Aggregation

Spanning Tree modes

ERS 8300 software release 2.2 introduces a Cisco-compatible Spanning
Tree mode. By default, the Nortel STG (NTSTG) is enabled, and all
BPDUs are sent on every MLT link. To use the Cisco-compatible Spanning
Tree mode, disable NTSTG — BPDUs are sent on only one link of the
aggregation group. See
configuration instructions.

Spanning Tree FastStart

When enabled on a port with no other bridges, Spanning Tree FastStart
brings the port up more quickly following switch initialization or a spanning
tree change. The port goes through the normal blocking and learning states
before the forwarding state, but the hold times for these states is the bridge
hello timer (2 seconds by default) instead of the bridge forward delay timer
(15 seconds by default). Thus, if FastStart is enabled on a port using the
defaults of 2 seconds for Hello time and 15 seconds for Forward Delay
time, it goes into the forwarding state in 4 seconds, instead of the usual 30
seconds. If the port sees a BPDU, it reverts to regular behavior.
Instead of disabling STP on a port, Nortel recommends enabling FastStart
on the port as an alternative.
FastStart is intended for access ports where only one device is connected
to the switch (as in workstations with no other spanning tree devices). It
may not be desirable to wait the usual 30 to 35 seconds for spanning tree
initialization and bridge learning.
Use Spanning Tree FastStart with caution. This procedure is contrary
to that specified in the IEEE 802.1D standard for Spanning Tree Protocol
(STP), in which a port enters the blocking state following the initialization
of the bridging device or from the disabled state when the port is enabled
through configuration.

Understanding STGs and VLANs

A VLAN can include all the ports in a given STG and there can be multiple
VLANs in an STG, but a VLAN never has more ports than exist in the STG.
The recommended practice is to plan STGs and then create VLANs.
In the ERS 8300 default configuration, a single STG encompasses all the
ports in the switch. For most applications, this configuration is sufficient.
The default STG is assigned ID 1 (STG1).
If a VLAN spans multiple switches, it must be within the same STG across
all switches; that is, the ID of the STG in which it is defined must be the
same across all devices.
Configuration — VLANs, Spanning Tree, and Static Link Aggregation using Device Manager
Copyright © 2005-2007, Nortel Networks
.
"Adding a link aggregation group" (page 110)
Nortel Ethernet Routing Switch 8300
NN46200-510 03.01 Standard
4.0 27 August 2007
for