LevelOne GTL-2691 - Manual (Page 243)

C HAPTER 8 | Spanning Tree Algorithm
Configuring Loopback Detection
– 243 –
An MST Region consists of a group of interconnected bridges that have the
same MST Configuration Identifiers (including the Region Name, Revision
Level and Configuration Digest – see "Configuring Multiple Spanning Trees"
on page 258 ). An MST Region may contain multiple MSTP Instances. An
Internal Spanning Tree (IST) is used to connect all the MSTP switches
within an MST region. A Common Spanning Tree (CST) interconnects all
adjacent MST Regions, and acts as a virtual bridge node for
communications with STP or RSTP nodes in the global network.
Figure 99: Common Internal Spanning Tree, Common Spanning Tree,
Internal Spanning Tree
MSTP connects all bridges and LAN segments with a single Common and
Internal Spanning Tree (CIST). The CIST is formed as a result of the
running spanning tree algorithm between switches that support the STP,
RSTP, MSTP protocols.
Once you specify the VLANs to include in a Multiple Spanning Tree Instance
(MSTI), the protocol will automatically build an MSTI tree to maintain
connectivity among each of the VLANs. MSTP maintains contact with the
global network because each instance is treated as an RSTP node in the
Common Spanning Tree (CST).
C ONFIGURING L OOPBACK D ETECTION
Use the Spanning Tree > Loopback Detection page to configure loopback
detection on an interface. When loopback detection is enabled and a port
or trunk receives it’s own BPDU, the detection agent drops the loopback
BPDU, sends an SNMP trap, and places the interface in discarding mode.
This loopback state can be released manually or automatically. If the
interface is configured for automatic loopback release, then the port will
only be returned to the forwarding state if one of the following conditions is
satisfied:
◆ The interface receives any other BPDU except for it’s own, or;
◆ The interfaces’s link status changes to link down and then link up again,
or;
Region 1
Region 4
Region 2 Region 3
CIST
IST
Region 1
Region 4
Region 2 Region 3
CST