Edge Port; P2P Port - D-Link xStack DES-3528 series User Manual

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xStack DES-3528/DES-3552 Series Layer 2 Stackable Fast Ethernet Managed Switch User Manual

Edge Port

The edge port is a configurable designation used for a port that is directly connected to a segment where a loop
cannot be created. An example would be a port connected directly to a single workstation. Ports that are designated
as edge ports transition to a forwarding state immediately without going through the listening and learning states. An
edge port loses its status if it receives a BPDU packet, immediately becoming a normal spanning tree port.

P2P Port

A P2P port is also capable of rapid transition. P2P ports may be used to connect to other bridges. Under RSTP, all
ports operating in full-duplex mode are considered to be P2P ports, unless manually overridden through configuration.
802.1D and 802.1w Compatibility
RSTP can interoperate with legacy equipment and is capable of automatically adjusting BPDU packets to 802.1D
format when necessary. However, any segment using 802.1D STP will not benefit from the rapid transition and rapid
topology change detection of RSTP. The protocol also provides for a variable used for migration in the event that
legacy equipment on a segment is updated to use RSTP.
The Spanning Tree Protocol (STP) operates on two levels:
1. On the switch level, the settings are globally implemented.
2. On the port level, the settings are implemented on a per user-defined group of ports basis.
STP LoopBack Prevention
When connected to other switches, STP is an important configuration in consistency for delivering packets to ports
and can greatly improve the throughput of your switch. Yet, even this function can malfunction with the emergence of
STP BPDU packets that occasionally loopback to the Switch, such as BPDU packets looped back from an
unmanaged switch connected to the Switch. To maintain the consistency of the throughput, the Switch now
implements the STP LoopBack prevention function.
When the STP LoopBack Detection function is enabled, the Switch will be protected against a loop occurring between
switches. Once a BPDU packet returns to the Switch, this function will detect that there is an anomaly occurring and
will place the receiving port in an error-disabled state. Consequentially, a message will be placed in the Switch's
Syslog and will be defined there as "BPDU Loop Back on Port #".
Setting the LoopBack Timer
The LoopBack timer plays a key role in the next step the switch will take to resolve this problem. Choosing a non-zero
value on the timer will enable the Auto-Recovery Mechanism. When the timer expires, the Switch will again look for its
returning BPDU packet on the same port. If no returning packet is received, the Switch will recover the port as a
Designated Port in the Discarding State. If another returning BPDU packet is received, the port will remain in a
blocked state, the timer will reset to the specified value, restart, and the process will begin again.
For those who choose not to employ this function, the LoopBack Recovery time must be set to zero. In this case,
when a BPDU packet is returned to the Switch, the port will be placed in a blocking state and a message will be sent
to the Syslog of the switch. To recover the port, the administrator must disable the state of the problematic port and
enable it again. This is the only method available to recover the port when the LoopBack Recover Time is set to 0.
Regulations and Restrictions for the LoopBack Detection Function
•
All versions of STP (STP and RSTP) can enable this feature.
•
May be configured globally (STP Global Bridge Settings).
•
Neighbor switches of the Switch must have the capability to forward BPDU packets. Switches the fail to meet
this requirement will disable this function for the port in question on the Switch.
•
The default setting for this function is disabled.
•
The default setting for the LoopBack timer is 60 seconds.
•
This setting will only be operational if the interface is STP-enabled.
The LoopBack Detection feature can only prevent BPDU loops on designated ports. It can detect a loop condition
occurring on the user's side connected to the edge port, but it cannot detect the LoopBack condition on the elected
root port of STP on another switch
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