AT-9000 Switch Command Line User’s Guide
Section VI: Spanning Tree Protocols
495
RSTP Loop Guard
Although RSTP is designed to detect and prevent the formation of loops in
a network topology, it is possible in certain circumstances for the protocol
to inadvertently create loops. This can happen in the unlikely situation
where a link between two RSTP devices remains active when there is an
cessation of BPDUs because of a hardware or software problem. The
RSTP loop guard feature is designed to prevent the formation of loops in
this situation.
Network devices running RSTP regularly transmit BPDUs to discover the
topology of a network and to the search for loops. These packets are used
by the devices to identify redundant physical paths to the root bridge and,
where loops exist, to determine the ports to be blocked.
The proper operation of RSTP relies on the flow of these packets. If there
is a hardware or software failure that interrupts their transmission or
reception, it is possible the protocol might mistakenly unblock one or more
ports in the spanning tree domain, causing a network loop.
The RSTP loop guard feature protects against this type of failure by
monitoring the ports on the switch for BPDUs from the other RSTP
devices. If a port stops receiving BPDUs without a change to its link state
(that is the link on a port stays up), the switch assumes that there is a
problem with RSTP on the other device and takes action depending on a
port’s role in the spanning tree domain. If the event happens on an
alternate port in the blocking state, the port is kept in that state. If this
occurs on a root or designated port in the forwarding state, the port’s state
is changed to the blocking state.
The switch activates loop guard only when there is a cessation in the flow
of BPDUs on a port whose link state has not changed. A port that never
receives BPDUs will not be affected by this feature.
A port that loop guard has placed in the blocking state remains in that state
until it begins to receive BPDUs again or you reset the switch.
Disconnecting the port, disabling or enabling a port with the management
software, or even disabling loop guard does not change a port’s blocking
state.
If a loop guard event occurs during a local or remote management
session, you will see this message displayed on the screen:
Loop Guard is triggered
If you configured the SNMP community strings on the switch, an SNMP
trap is sent to your management workstations to notify you of the event.
This event does not generate an entry in the switch’s log.
Содержание AT-9000/28
Страница 4: ......
Страница 26: ...Contents 26...
Страница 30: ...Tables 30...
Страница 36: ...36 Section I Getting Started...
Страница 70: ...Chapter 2 Starting a Management Session 70 Section I Getting Started...
Страница 96: ...96 Section II Basic Operations...
Страница 142: ...Chapter 6 Basic Switch Management Commands 142 Section II Basic Operations...
Страница 220: ...Chapter 9 IPv4 and IPv6 Management Addresses 220 Section II Basic Operations...
Страница 244: ...Chapter 10 IPv4 and IPv6 Management Address Commands 244 Section II Basic Operations...
Страница 264: ...Chapter 12 SNTP Client Commands 264 Section II Basic Operations...
Страница 298: ...Chapter 15 Enhanced Stacking 298 Section II Basic Operations...
Страница 312: ...Chapter 16 Enhanced Stacking Commands 312 Section II Basic Operations...
Страница 318: ...Chapter 17 Port Mirror 318 Section II Basic Operations...
Страница 324: ...Chapter 18 Port Mirror Commands 324 Section II Basic Operations Example awplus show mirror...
Страница 350: ...Chapter 21 Multicast Commands 350 Section II Basic Operations...
Страница 352: ...352 Section III File System...
Страница 360: ...Chapter 22 File System 360 Section III File System...
Страница 383: ...AT 9000 Switch Command Line User s Guide Section III File System 383 Example awplus show boot...
Страница 386: ...Chapter 25 Boot Configuration File Commands 386 Section III File System...
Страница 398: ...Chapter 26 File Transfers 398 Section III File System...
Страница 406: ...Chapter 27 File Transfer Commands 406 Section III File System...
Страница 408: ...408 Section IV Event Messages...
Страница 430: ...Chapter 30 Syslog Client 430 Section IV Event Messages...
Страница 438: ...438 Section V Port Trunks...
Страница 448: ...Chapter 32 Static Port Trunks 448 Section V Port Trunks...
Страница 480: ...480 Section VI Spanning Tree Protocols...
Страница 500: ...Chapter 36 Spanning Tree and Rapid Spanning Tree Protocols 500 Section VI Spanning Tree Protocols...
Страница 520: ...Chapter 38 STP Commands 520 Section VI Spanning Tree Protocols...
Страница 542: ...Chapter 40 RSTP Commands 542 Section VI Spanning Tree Protocols Example awplus show spanning tree...
Страница 558: ...558 Section VII Virtual LANs...
Страница 600: ...Chapter 42 Port based and Tagged VLAN Commands 600 Section VII Virtual LANs...
Страница 634: ...Chapter 44 GARP VLAN Registration Protocol Commands 634 Section VII Virtual LANs...
Страница 670: ...Chapter 47 Private Port VLANs 670 Section VII Virtual LANs...
Страница 692: ...Chapter 50 VLAN Stacking 692 Section VII Virtual LANs...
Страница 698: ...Chapter 51 VLAN Stacking Commands 698 Section VII Virtual LANs...
Страница 700: ...700 Section VIII Port Security...
Страница 748: ...Chapter 54 802 1x Port based Network Access Control 748 Section VIII Port Security...
Страница 790: ...Chapter 55 802 1x Port based Network Access Control Commands 790 Section VIII Port Security...
Страница 792: ...792 Section IX Simple Network Management Protocols...
Страница 804: ...Chapter 56 SNMPv1 and SNMPv2c 804 Section X Simple Network Management Protocols...
Страница 852: ...852 Section X Network Management...
Страница 976: ...Chapter 63 Address Resolution Protocol ARP 976 Section X Network Management...
Страница 1090: ...1090 Section XI Management Security...
Страница 1114: ...Chapter 71 Telnet Server 1114 Section XI Management Security...
Страница 1122: ...Chapter 73 Telnet Client 1122 Section XI Management Security...
Страница 1126: ...Chapter 74 Telnet Client Commands 1126 Section XI Management Security...
Страница 1138: ...Chapter 75 Secure Shell SSH Server 1138 Section XI Management Security...
Страница 1158: ...Chapter 78 Non secure HTTP Web Browser Server Commands 1158 Section XI Management Security...
Страница 1186: ...Chapter 80 Secure HTTPS Web Browser Server Commands 1186 Section XI Management Security...
Страница 1202: ...Chapter 81 RADIUS and TACACS Clients 1202 Section XI Management Security...
Страница 1230: ...Chapter 82 RADIUS and TACACS Client Commands 1230 Section XI Management Security...
Страница 1244: ...Chapter System Monitoring Commands 1244...
Страница 1278: ...Index 1278 Configuration mode 644 659 VLAN SET MACADDRESS command Port Interface mode 644 661 W WRITE command 75 94 385...