DES-3550 Layer 2
Fast Ethernet Switch User’s Guide
56
In addition to setting Spanning Tree parameters for use on the switch level, the Switch allows
for the configuration of groups of ports, each port-group of which will have its own spanning
tree, and will require some of its own configuration settings. An STP Group will use the
switch-level parameters entered above, with the addition of
Port Priority
and
Port Cost
.
An STP Group spanning tree works in the same way as the switch-level spanning tree, but the
root bridge concept is replaced with a root port concept. A root port is a port of the group that
is elected based on port priority and port cost, to be the connection to the network for the
group. Redundant links will be blocked, just as redundant links are blocked on the switch
level.
The STP on the switch level blocks redundant links between switches (and similar network
devices). The port level STP will block redundant links within an STP Group.
It is advisable to define an STP Group to correspond to a VLAN group of ports.
The following fields can be set:
Parameter
Description
From/To < Port 1 >
A consecutive group of ports may be configured starting with the selected
port.
State < Disabled >
This drop-down menu allows you to
Enable
or
Disable
STP for the selected
group of ports.
Cost < 0 >
A Port Cost can be set from
1
to
200000000
. The lower the number, the
greater the probability the port will be chosen to forward packets.
Default port cost:
100Mbps port = 200000
Gigabit ports = 20000
Priority
<128>
A Port Priority can be from
0
to
240
. The lower the number, the greater the
probability the port will be chosen as the Root Port.
Migration
<No>
Select Y
es
or
No
. Choosing Yes will enable the port to migrate from 802.1d
STP status to 802.1w RSTP status. RSTP can coexist with standard STP,
however the benefits of RSTP are not realized on a port where an 802.1d
network connects to an 802.1w enabled network. Migration should be
enabled (yes) on ports connected to network stations or segments that will
be upgraded to 802.1w RSTP on all or some portion of the segment.
Edge
<No>
Select
Yes
or
No.
Choosing Yes designates the port as an edge port. Edge
ports cannot create loops, however an edge port can lose edge port status if
a topology change creates a potential for a loop. An edge port normally
should not receive BPDU packets. If a BPDU packet is received, it
automatically loses edge port status. No indicates the port does not have
edge port status.
P2P <No>
Select
Yes
or
No
. Choosing
Yes
indicates a point-to-point (p2p) shared link.
These are similar to edge ports however, they are restricted in that a p2p
port must operate in full-duplex. Like edge ports, p2p ports transition to a
forwarding state rapidly thus benefiting from RSTP.
Click
Apply
to implement the changes made.
