Planet IGS-801T [72/120] User s manual of igs 801m

User’s Manual of IGS-801M

The following are t

he user-configurable STP parameters for the port or port group level:

le Description Default Value Variab

Port Priority

A relative priority for each

port –lower numbers give a higher priority

elected as the root port

128

and a greater chance of a given port being

Port Cost

A value used by STP to evaluate paths –

STP calculates path costs and selects the

inimum cost as the active

200,000-100Mbps Fast Ethernet ports

20,000-1000Mbps Gigabit Ethernet

ports

0 - Auto

path with the m

Default Spanning-Tree Configuration

Feature Default Value

Enable state P disabled for all ports ST

Port priority 128

Port cost 0

Bridge Priority 32,768

3. Illus ation of STP

A simple illustration of three switches connecte in the below diagram. In this example, you can

anticip problems if the

If switch A broadcasts a packet to switch B, sw will broadcast it to back to

switch A and so on. The broadcast packet will be p d indefinitely in a loop, potentially causing a network failure. In this

example, STP breaks the loop by blocking the connection between switch B and C. The decision to block a particular

connection is based on the STP calculation of the most current Bridge and Port settings.

Now, if switch A broadcasts a packet to switch C, then switch C will drop the packet at port 2 and the broadcast will end

there. Setting-up STP using values other than the defaults, can be complex. Therefore, you are advised to keep the

default factory settings and S P will automatically assign root bridges/ports and block loop connections. Influencing STP

choose a particular switch as the root bridge using the Priority setting, or influencing STP to choose a particular port to

block using the Port Priority a

d in a loop is depicted

ate some major network STP assistance is not applied.

itch B will broadcast it to switch C, and switch C

asse

nd Port Cost settings is, however, relatively straight forward.