DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

another can be filtered from the network. The entry may specified as a source, a destination, or both (switch must be in IP Routing mode).

Spanning Tree

The IEEE 802.1D Spanning Tree Protocol allows for the blocking of links between switches that form loops within the network. When multiple links between switches are detected, a primary link is established. Duplicated links are blocked from use and become standby links. The protocol allows for the duplicate links to be used in the event of a failure of the primary link. Once the Spanning Tree Protocol is configured and enabled, primary links are established and duplicated links are blocked automatically. The reactivation of the blocked links (at the time of a primary link failure) is also accomplished automatically – without operator intervention.

The DES-3326 STP allows two levels of spanning trees to be configured. The first level constructs a spanning tree on the links between switches. This is referred to as the Switch or Global level. The second level is on a port group basis. Groups of ports are configured as being members of a spanning tree and the algorithm and protocol are applied to the group of ports. This is referred to as the Port or VLAN level.

On the switch level, STP calculates the Bridge Identifier for each switch and then sets the Root Bridge and the Designated Bridges.

On the port level, STP sets the Root Port and the Designated Ports.

The following are the user-configurable STP parameters for the switch level:

ameter

 

Description

 

 

Default

 

 

 

 

 

 

Value

 

 

 

Bridge Identifier

A combination of the User-

32768 + MAC

 

 

set priority and the switch’s

 

(Not

user-

MAC address.

The

Bridge

 

configurable

Identifier

consists

of two

 

except by setting

parts: a 16-bit priority and

 

priority below)

a 48-bit Ethernet MAC

 

 

 

address

 

 

 

 

 

 

 

 

Priority

 

A relative priority for each

32768

 

 

switch – lower numbers give

 

 

 

a higher priority and a

 

 

 

greater chance of a given

 

 

 

switch being elected as the

 

 

 

root bridge

 

 

 

 

 

 

 

 

Hello Time

 

The length of time between

2 seconds

 

 

broadcasts

of

the

hello

 

 

 

message by the switch

 

 

 

 

 

Maximum

Age

Measures the age of a

20 seconds

Timer

 

received BPDU for a port

 

 

 

and ensures that the BPDU

 

 

 

is discarded when its age

 

 

 

exceeds the value of the

 

 

 

maximum age timer.

 

 

 

 

 

 

Forward

Delay

The amount time spent by a

15 seconds

Timer

 

port in the learning and

 

 

 

listening states waiting for a

 

30

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D-Link DES-3326 manual Spanning Tree, Ameter Description Default Value