Cisco WS-X6248-RJ-45 - Catalyst 6000 Expansion Module Bedienungsanleitung PDF herunterladen (Seite 21)

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For this alteration, a VLAN database was introduced into Cisco IOS for the Cisco Catalyst 6500 as a method for

immediately saving VTP updates for VTP Clients and Servers. This VLAN database is in the form of a separate ﬁle

inNVRAM,calledthevlan.datﬁle.Thisis where the VTP/VLAN information is stored for VTP Client or VTP Server

systems. The entire VTP/VLAN conﬁguration is not backed up to the Startup Conﬁg ﬁle in NVRAM when a copy

run start command is issued on these systems.

This does not apply to systems running as VTP transparent. VTP Transparent systems back up the entire VTP/VLAN

conﬁguration to the Startup Conﬁg ﬁle in NVRAM when you issue a copy run start command.

Spanning Tree Protocol (STP)

The Spanning Tree Protocol (STP) is used to prevent loops while implementing redundancy in Layer2 environments.

STP is based on one of severalIEEE standards: 802.1d, 802.1s, or 802.1w. IEEE 802.1d is the original spanning-tree

implementation that is based on timer mechanisms to detect and respond to network topology changes. The Cisco

implementation of IEEE 802.1d in both CatOS and Cisco IOS Software is called Per-VLAN Spanning Tree Plus

(PVST+). 802.1s refers to theIEEE versionof MultipleSpanning Trees(MST), which allows a scalable spanning-tree

implementation for environments with a large number of VLANs. IEEE 802.1w is the standard for Rapid Spanning

Tree (RSTP);this protocol improvesthe convergence timefrom the originalIEEE 802.1d implementationby moving

from a timer-based system to a change notiﬁcation-based system. This section presents the conﬁguration differences

for PVST+ (802.1d) only.

Basic STP Conﬁguration

PVST+ Enhancements

Spanning Tree UplinkFast allows for faster convergence in a Layer 2 network after a direct root link failure. If a link

from one bridge to the root bridge goes down, then the bridge will move one blocking port to forwarding

immediatelyratherthanwaitingforthenormalspanningtreetimersto expire. This brings the convergence time from

50 seconds to 3 to 5 seconds for this type of failure.

In the case of an indirect failure in a Layer 2 network, Spanning Tree BackboneFast reduces the convergence time by

the “maximum age” timer value (which defaults to 20 seconds).

Spanning Tree PortFast causes an access port to enter the forwarding state immediately, bypassing the listening and

learning states. The feature is used on switch ports connected to a single workstation, IP Phone, server, etc. It allows

these devices to connect to the network immediately, rather than waiting for spanning tree to converge. PortFast

mode is supported on nontrunking access ports only because these ports typically do not transmit or receive bridge

protocol data units (BPDUs) from attached devices.

CatOS Cisco IOS Software

set spantree root 10 dia 5 hello 2

set spantree root sec 11 dia 5 hello 2

set spantree priority 4096 10,11

IOS(config)# spanning-tree vlan 10 root

primary dia 5 hello 2

IOS(config)# spanning-tree vlan 11 root

sec dia 5 hello 2

IOS(config)# spanning-tree vlan 10 pri 4096

IOS(config)# spanning-tree vlan 11 pri 4096

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Cisco WS-X6248-RJ-45 - Catalyst 6000 Expansion Module Bedienungsanleitung Seite 21