Extreme 3804 Mode D'Emploi

7-4

S

UMMIT

 S

WITCH

 I

NSTALLATION

 

AND

 U

SER

 G

UIDE

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PANNING

 T

REE

 P

ROTOCOL

 (STP)

Within a single STPD, you must be extra careful when configuring your VLANs. 

 illustrates a network that has been incorrectly set up using a single STPD so 

that the STP configuration disables the ability of the switches to forward VLAN traffic.

Figure 7-2: Tag-based STP configuration

The tag-based network in 

 has the following configuration:

Switch 1 contains VLAN Marketing and VLAN Sales.

Switch 2 contains VLAN Engineering and VLAN Sales.

Switch 3 contains VLAN Marketing, VLAN Engineering, and VLAN Sales.

The tagged trunk connections for three switches form a triangular loop that is not 
permitted in an STP topology.

All VLANs in each switch are members of the same STPD.

STP may block traffic between Switch 1 and Switch 3 by disabling the trunk ports for 
that connection on each switch.

Switch 2 has no ports assigned to VLAN marketing. Therefore, if the trunk for VLAN 
marketing on Switches 1 and 3 is blocked, the traffic for VLAN marketing will not be 
able to traverse the switches.

Marketing & Sales

Marketing, Sales & Engineering

Sales & Engineering

Switch 1

Switch 3

Switch 2

Summit.bk : 7STP.FM  Page 4  Thursday, June 18, 1998  9:27 AM