Install guide

38 Release Note
Rapier Switch Software Release 2.1.0
C613-10200-01 Rev A
The Egress Rules
Once the Forwarding Process has determined which ports and transmission
queues to forward a frame from, the Egress Rules for each port determine
whether or not the outgoing frame is VLAN-tagged with its VID. (See “Virtual
LANs” on page 25).
Whether outgoing frames for a VLAN are tagged when transmitted from the
port is configured when the port is added to the VLAN, and can be changed
later, using this commands:
ADD VLAN={vlanname|1..4094} PORT={port-list|ALL}
[FRAME={TAGGED|UNTAGGED}]
SET VLAN={vlanname|1..4094} PORT={port-list|ALL}
FRAME={UNTAGGED|TAGGED}
Spanning Tree Protocol (STP)
The Spanning Tree Protocol (STP) makes it possible to automatically disable
redundant paths in a network to avoid loops, and enable them when a fault in
the network means they are needed to keep traffic flowing. A sequence of
LANs and switches may be connected together in an arbitrary physical
topology resulting in more than one path between any two switches. If a loop
exists, frames transmitted onto the extended LAN would circulate around the
loop indefinitely, decreasing the performance of the extended LAN. On the
other hand, multiple paths through the extended LAN provide the opportunity
for redundancy and backup in the event of a bridge experiencing a fatal error
condition.
The spanning tree algorithm ensures that the extended LAN contains no loops
and that all LANs are connected by:
■
Detecting the presence of loops and automatically computing a logical
loop-free portion of the topology, called a spanning tree. The topology is
dynamically pruned to a spanning tree by declaring a port redundant, and
placing the port into a non-’Forwarding’ state.
■
Automatically recovering from a switch failure that would partition the
extended LAN by reconfiguring the spanning tree to use redundant
switches.
The logical tree computed by the spanning tree algorithm has the following
properties:
■
A single switch, called the root bridge, forms a unique root to the tree. The
root bridge is the bridge with the lowest Bridge ID. Each switch in an
extended LAN is uniquely identified by its Bridge ID, which comprises the
switch’s root priority (a spanning tree parameter) and its MAC address.
■
Each switch or LAN in the tree, except the root bridge, has a unique parent.
■
The unique parent of a LAN is the designated bridge for the LAN. Each LAN
has a single switch, called the designated bridge, that logically connects the
LAN to the next LAN closer to the root bridge. Each port connecting a
switch to a LAN has an associated cost. The root path cost is the sum of the
costs for each port between the switch and the root bridge. The designated
bridge for a LAN is the switch on the LAN with the lowest root path cost,
and therefore logically closer to the root bridge. If two switch’s on the same
LAN have the same lowest root path cost, the switch with the lowest
bridge ID is elected the designated bridge.