Chapter 7
| Spanning Tree Algorithm
Overview
– 198 –
Figure 110: STP Root Ports and Designated Ports
Once a stable network topology has been established, all bridges listen for Hello
BPDUs (Bridge Protocol Data Units) transmitted from the Root Bridge. If a bridge
does not get a Hello BPDU after a predefined interval (Maximum Age), the bridge
assumes that the link to the Root Bridge is down. This bridge will then initiate
negotiations with other bridges to reconfigure the network to reestablish a valid
network topology.
RSTP
– RSTP is designed as a general replacement for the slower, legacy STP. RSTP is
also incorporated into MSTP. RSTP achieves much faster reconfiguration (i.e.,
around 1 to 3 seconds, compared to 30 seconds or more for STP) by reducing the
number of state changes before active ports start learning, predefining an alternate
route that can be used when a node or port fails, and retaining the forwarding
database for ports insensitive to changes in the tree structure when
reconfiguration occurs.
MSTP
– When using STP or RSTP, it may be difficult to maintain a stable path
between all VLAN members. Frequent changes in the tree structure can easily
isolate some of the group members. MSTP (which is based on RSTP for fast
convergence) is designed to support independent spanning trees based on VLAN
groups. Using multiple spanning trees can provide multiple forwarding paths and
enable load balancing. One or more VLANs can be grouped into a Multiple
Spanning Tree Instance (MSTI). MSTP builds a separate Multiple Spanning Tree
(MST) for each instance to maintain connectivity among each of the assigned VLAN
groups. MSTP then builds a Internal Spanning Tree (IST) for the Region containing
all commonly configured MSTP bridges.
Figure 111: MSTP Region, Internal Spanning Tree, Multiple Spanning Tree
x
Designated
Root
Designated
Port
Designated
Bridge
x
x
x
Root
Port
x
Region R
IST
(for this Region)
MST 1
MST 2
Содержание GTL-2881
Страница 30: ...Figures 30 Figure 450 Showing RIP Peer Information 669 Figure 451 Resetting RIP Statistics 670 ...
Страница 34: ...Section I Getting Started 34 ...
Страница 48: ...Section II Web Configuration 48 Unicast Routing on page 651 ...
Страница 151: ...Chapter 4 Interface Configuration VLAN Trunking 151 Figure 69 Configuring VLAN Trunking ...
Страница 152: ...Chapter 4 Interface Configuration VLAN Trunking 152 ...
Страница 229: ...Chapter 8 Congestion Control Automatic Traffic Control 229 Figure 135 Configuring ATC Interface Attributes ...
Страница 230: ...Chapter 8 Congestion Control Automatic Traffic Control 230 ...
Страница 596: ...Chapter 14 Multicast Filtering Multicast VLAN Registration for IPv6 596 ...
Страница 620: ...Chapter 15 IP Configuration Setting the Switch s IP Address IP Version 6 620 ...
Страница 670: ...Chapter 18 Unicast Routing Configuring the Routing Information Protocol 670 Figure 451 Resetting RIP Statistics ...
Страница 672: ...Section III Appendices 672 ...
Страница 678: ...Appendix A Software Specifications Management Information Bases 678 ...
Страница 688: ...Appendix C License Statement GPL Code Statement Notification of Compliance 688 ...
Страница 696: ...Glossary 696 ...
Страница 706: ...GTL 2881 GTL 2882 E112016 ST R01 ...