經過實驗理解交換的三個fast特性

時間 2020-02-07

標籤經過實驗理解交換三個 fast 特性简体版

原文原文鏈接

拓撲如上圖，Sw1爲根交換機，Sw2爲備份根交換機，Sw3爲接入層交換機。 ide

配置：SW1spanning-tree vlan 1 priority 8192 SW2：spanning-tree vlan 1 priority 16384。 oop

經過在ＳＷ３上查看。 this

SW3#show span brief spa

VLAN1
Spanning tree enabled protocol ieee
Root ID    Priority    8192
             Address     cc00.0dd4.0000
             Cost        19
             Port        4 (FastEthernet0/3)
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec orm

Bridge ID Priority    32768
             Address     cc02.0dd4.0000
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec
             Aging Time 300 blog

Interface                                   Designated
Name                 Port ID Prio Cost Sts Cost Bridge ID            Port ID
-------------------- ------- ---- ----- --- ----- -------------------- -------
FastEthernet0/2      128.3    128    19 BLK    19 16384 cc01.0dd4.0000 128.3
FastEthernet0/3      128.4    128    19 FWD     0 8192 cc00.0dd4.0000 128.4
FastEthernet0/4      128.5    128    19 FWD    19 32768 cc02.0dd4.0000 128.5 接口

1、Portfast特性。 backbone

開啓portfast特性的端口又叫快速端口，配置在接口端口上，鏈接主機或路由器的端口上啓用，不能與鏈接交換機的端口啓用。不然或出現環路。默認的狀況下接口從接入到Forwarding狀態須要通過30s的時間，通過listening、learning狀態。驗證： ci

將SW3的Fa0/4關閉，開啓degbu spanning-tree event。路由

SW3(config)#inter f0/4
SW3(config-if)#no shu
SW3(config-if)#
*Mar 1 00:03:00.591: STP: VLAN1 Fa0/4 -> listening
*Mar 1 00:03:03.355: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/4, changed state to up
*Mar 1 00:03:15.611: STP: VLAN1 Fa0/4 -> learning
*Mar 1 00:03:30.631: STP: VLAN1 sent Topology Change Notice on Fa0/3
*Mar 1 00:03:30.635: STP: VLAN1 Fa0/4 -> forwarding

下面開啓Portfast特性。

在SW3的Fa0/4接口下:

SW3(config-if)#spanning-tree portfast
%Warning: portfast should only be enabled on ports connected to a single host.
Connecting hubs, concentrators, switches, bridges, etc.to this interface
when portfast is enabled, can cause temporary spanning tree loops.
Use with CAUTION

%Portfast has been configured on FastEthernet0/4 but will only
have effect when the interface is in a non-trunking mode.

SW3(config)#inter f0/4

SW3(config-if)#no shu
SW3(config-if)#
*Mar 1 00:05:36.435: STP: VLAN1 Fa0/4 ->jump to forwarding from blocking
*Mar 1 00:05:39.171: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/4, changed state to up

直接進入Forwarding狀態。節省30s。

2、uplinkfast。

uplinkfast也叫快速上行端口，在上圖所示的拓撲中，接入交換機有兩條上行鏈路若是主鏈路down，備份鏈路須要通過30s的時間纔可以恢復到Forwarding狀態。

驗證：

在SW3上將Fa0/3端口。

SW3(config)#int f0/3
SW3(config-if)#shu
SW3(config-if)#
*Mar 1 00:06:47.763: STP: VLAN1 Fa0/3 -> blocking
*Mar 1 00:06:47.763: STP: VLAN1 new root port Fa0/2, cost 38
*Mar 1 00:06:47.835: STP: VLAN1 Fa0/2 -> listening
*Mar 1 00:06:49.687: %LINK-5-CHANGED: Interface FastEthernet0/3, changed state to administratively down
*Mar 1 00:06:49.687: STP: VLAN1 sent Topology Change Notice on Fa0/2
*Mar 1 00:06:50.687: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/3, changed state to down
*Mar 1 00:07:02.855: STP: VLAN1 Fa0/2 -> learning
*Mar 1 00:07:17.875: STP: VLAN1 sent Topology Change Notice on Fa0/2
*Mar 1 00:07:17.879: STP: VLAN1 Fa0/2 -> forwarding

如今啓用uplinkfast，SW3上全局啓用。uplinkfast通常在接×××換機上啓用。核心和匯聚交換機最好不要啓用。

SW3(config)#spanning-tree uplinkfast

SW3(config-if)#shut

SW3(config-if)#
*Mar 1 02:53:35.555: STP: VLAN1 Fa0/3 -> blocking
*Mar 1 02:53:35.555: STP: VLAN1 new root port Fa0/2, cost 3038
*Mar 1 02:53:35.555: %SPANTREE_FAST-7-PORT_FWD_UPLINK: VLAN1 FastEthernet0/2 moved to Forwarding (UplinkFast).

備份鏈路接口Fa0/2直接進入Forwarding狀態。節省30s。

注：啓用uplinkfast之後，生成樹的優先級將變成49152，接口的生成樹cost增長3000。

SW3#show span br

VLAN1
Spanning tree enabled protocol ieee uplinkfast enabled
Root ID    Priority    8192
             Address     cc00.0dd4.0000
             Cost        3038
             Port        3 (FastEthernet0/2)
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority    49152
             Address     cc02.0dd4.0000
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec
             Aging Time 300

Interface                                   Designated
Name                 Port ID Prio Cost Sts Cost Bridge ID            Port ID
-------------------- ------- ---- ----- --- ----- -------------------- -------
FastEthernet0/2      128.3    128 3019 FWD    19 16384 cc01.0dd4.0000 128.3
FastEthernet0/3      128.4    128 3019 BLK     0 8192 cc00.0dd4.0000 128.4
FastEthernet0/4      128.5    128 3019 FWD 3038 49152 cc02.0dd4.0000 128.5

3、Backbonefast（快速骨幹）

在上圖SW1和SW2的直連鏈路若是出現故障，那麼SW2將沒法識別根交換機的位置，SW2就會發送次級BPDU標識本身是根，SW3的阻塞端口收到次級BPDU之後，將會進入老化時間，而後通過listening、learning狀態才能到達Forwarding狀態，這一過程須要50s的時間。

驗證：

將SW2的Fa0/1關閉。

SW2(config)#inter fa0/1

SW2(config-if)#shutdown

SW3#
*Mar 1 01:02:30.967: STP: VLAN1 heard root 16384-cc01.0dd4.0000 on Fa0/2
*Mar 1 01:02:30.967: current Root has 8192-cc00.0dd4.0000
*Mar 1 01:02:32.931: STP: VLAN1 heard root 16384-cc01.0dd4.0000 on Fa0/2
*Mar 1 01:02:32.931: current Root has 8192-cc00.0dd4.0000
*Mar 1 01:02:34.919: STP: VLAN1 heard root 16384-cc01.0dd4.0000 on Fa0/2
*Mar 1 01:02:34.919: current Root has 8192-cc00.0dd4.0000
*Mar 1 01:02:36.907: STP: VLAN1 heard root 16384-cc01.0dd4.0000 on Fa0/2
*Mar 1 01:02:36.907: current Root has 8192-cc00.0dd4.0000
*Mar 1 01:02:38.927: STP: VLAN1 heard root 16384-cc01.0dd4.0000 on Fa0/2
*Mar 1 01:02:38.927: current Root has 8192-cc00.0dd4.0000
*Mar 1 01:02:40.931: STP: VLAN1 heard root 16384-cc01.0dd4.0000 on Fa0/2
*Mar 1 01:02:40.931: current Root has 8192-cc00.0dd4.0000
*Mar 1 01:02:42.923: STP: VLAN1 heard root 16384-cc01.0dd4.0000 on Fa0/2
*Mar 1 01:02:42.923: current Root has 8192-cc00.0dd4.0000
*Mar 1 01:02:44.931: STP: VLAN1 heard root 16384-cc01.0dd4.0000 on Fa0/2
*Mar 1 01:02:44.931: current Root has 8192-cc00.0dd4.0000
*Mar 1 01:02:46.935: STP: VLAN1 heard root 16384-cc01.0dd4.0000 on Fa0/2
*Mar 1 01:02:46.935: current Root has 8192-cc00.0dd4.0000
*Mar 1 01:02:48.927: STP: VLAN1 heard root 16384-cc01.0dd4.0000 on Fa0/2
*Mar 1 01:02:48.927: current Root has 8192-cc00.0dd4.0000
*Mar 1 01:02:48.987: STP: VLAN1 Fa0/2 -> listening
*Mar 1 01:02:50.023: STP: VLAN1 Topology Change rcvd on Fa0/2
*Mar 1 01:02:50.027: STP: VLAN1 sent Topology Change Notice on Fa0/3
*Mar 1 01:03:04.007: STP: VLAN1 Fa0/2 -> learning
*Mar 1 01:03:19.031: STP: VLAN1 sent Topology Change Notice on Fa0/3
*Mar 1 01:03:19.031: STP: VLAN1 Fa0/2 -> forwarding
通過50s的時間。

配置backbonefast，在全部的交換機上全局啓用。spanning-tree backbonefast

配置backbonefast特性之後，當SW3收到次級BPDU時，他會向根交換機SW1發送RLQ BPDU（根鏈路查詢BPDU）查詢根交換機是否仍然處於激活狀態，SW1收到RLQ BPDU之後會發送一個RLQ 確認。SW3收到RLQ的確認之後會將收到次級BPDU的阻塞端口跳過老化時間，直接進入listening狀態，節省20s的時間。

SW2(config)#inter fa0/1

SW2(config-if)#shutdown

SW3#

*Mar 1 01:05:11.735: STP: VLAN1 heard root 16384-cc01.0dd4.0000 on Fa0/2 *Mar 1 01:05:11.735: current Root has 8192-cc00.0dd4.0000 *Mar 1 01:05:11.815: STP: VLAN1 Fa0/2 -> listening *Mar 1 01:05:11.975: STP: VLAN1 Topology Change rcvd on Fa0/2 *Mar 1 01:05:11.975: STP: VLAN1 sent Topology Change Notice on Fa0/3 *Mar 1 01:05:26.835: STP: VLAN1 Fa0/2 -> learning *Mar 1 01:05:41.859: STP: VLAN1 sent Topology Change Notice on Fa0/3 *Mar 1 01:05:41.859: STP: VLAN1 Fa0/2 -> forwarding

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