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DGS-3024 Gigabit Ethernet Switch Manual
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
A consecutive group of ports may be configured starting with the selected port.
External Cost (0 =
Auto)
This defines a metric that indicates the relative cost of forwarding packets to the
specified port list. Port cost can be set automatically or as a metric value. The
default value is 0 (auto).
0 (auto) - Setting 0 for the external cost will automatically set the speed for
forwarding packets to the specified port(s) in the list for optimal efficiency.
Default port cost: 100Mbps port = 200000. Gigabit port = 20000.
value 1-200000000 - Define a value between 1 and 200000000 to determine the
external cost. The lower the number, the greater the probability the port
will be chosen to forward packets.
Hello Time
The time interval between the transmission of configuration messages by the des-
ignated port, to other devices on the bridged LAN, thus stating that the Switch is still
functioning. The user may choose a time between 1 and 10 seconds. The default is
2 seconds. This field is only operable when the Switch is enabled for MSTP.
Migration
Setting this parameter as Yes will set the ports to send out BDPU packets to other
bridges, requesting information on their STP setting If the Switch is configured for
RSTP, the port will be capable to migrate from 802.1d STP to 802.1w RSTP. If the
Switch is configured for MSTP, the port is capable of migrating from 802.1d STP to
802.1s MSTP. RSTP and MSTP can coexist with standard STP, however the
benefits of RSTP and MSTP are not realized on a port where an 802.1d network
connects to an 802.1w or 802.1s enabled network. Migration should be set as yes
on ports connected to network stations or segments that are capable of being
upgraded to 802.1w RSTP or 802.1s MSTP on all or some portion of the segment.
Edge
Choosing the True parameter 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.
Choosing the False parameter indicates that the port does not have edge port
status.
P2P
Choosing the True parameter indicates a point-to-point (P2P) shared link. P2P ports
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. A p2p value of false indicates that the port cannot
have p2p status. Auto allows the port to have p2p status whenever possible and
operate as if the p2p status were true. If the port cannot maintain this status, (for
example if the port is forced to half-duplex operation) the p2p status changes to
o
p
erate as if the
p
2
p
value were False. The default settin
g
for this
p
arameter is
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