pty:32768
mac:0004.2xxx.0ec0
+----+10
|24_1+--------------+
+--+-+ |
|2 |
| |
|2 |10(X)
+--+-+ +--+-+
|24_2+-----------+12_1|
+----+6 6+----+
pty:32768 pty:32768
mac:0003.fxxx.8580 mac:0004.9xxx.23c0
ROOT
デフォルトの設定だと、24_2のMACが最小なのでルートになる。
各switchでの、show spanning-treeの結果（最初の部分だけ）
cata2924_01#sho spanning-tree Spanning tree 1 is executing the IEEE compatible Spanning Tree protocol Bridge Identifier has priority 32768, address 0004.2xxx.0ec0 ※自分のmac Configured hello time 2, max age 20, forward delay 15 Current root has priority 32768, address 0003.fe67.8580 ※root bridgeのMAC Root port is 14, cost of root path is 19 Topology change flag not set, detected flag not set, changes 15 Times: hold 1, topology change 35, notification 2 hello 2, max age 20, forward delay 15 Timers: hello 0, topology change 0, notification 0 cata2924_02#sho spanning-tree Spanning tree 1 is executing the IEEE compatible Spanning Tree protocol Bridge Identifier has priority 32768, address 0003.fxxx.8580 ※自分のMAC Configured hello time 2, max age 20, forward delay 15 We are the root of the spanning tree ※自分がrootである Topology change flag not set, detected flag not set, changes 14 Times: hold 1, topology change 35, notification 2 hello 2, max age 20, forward delay 15 Timers: hello 1, topology change 0, notification 0 cata2912_01#sho spanning-tree Spanning tree 1 is executing the IEEE compatible Spanning Tree protocol Bridge Identifier has priority 32768, address 0004.9xxx.23c0 ※自分のMAC Configured hello time 2, max age 20, forward delay 15 Current root has priority 32768, address 0003.fxxx.8580 ※rootのMAC Root port is 18, cost of root path is 19 Topology change flag not set, detected flag not set, changes 14 Times: hold 1, topology change 35, notification 2 hello 2, max age 20, forward delay 15 Timers: hello 0, topology change 0, notification 0ここでdebugを有効にしてから、24_1と12_1間のケーブルを抜いて、さして見る。
cata2924_01#debug spantree events Spanning Tree event debugging is on cata2924_01# 02:48:08: %LINK-3-UPDOWN: Interface FastEthernet0/10, changed state to down 02:48:08: ST: sent Topology Change Notice on FastEthernet0/2 vlan 1 02:48:08: ST: FastEthernet0/10 vlan 1 -> blocking 02:48:09: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/10, changed state to down 02:48:16: %LINK-3-UPDOWN: Interface FastEthernet0/10, changed state to up 02:48:16: ST: FastEthernet0/10 vlan 1 -> listening 02:48:17: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/10, changed state to up 02:48:31: ST: FastEthernet0/10 vlan 1 -> learning 02:48:47: ST: sent Topology Change Notice on FastEthernet0/2 vlan 1 02:48:47: ST: FastEthernet0/10 vlan 1 -> forwarding cata2924_01#listening -> learning -> forwarding まで１５秒ずつ、合計３０秒かかっている。 15というのはforward delay の値である。それでは、24_1で、forward delayの値を変えて見よう。
cata2924_01(config)#spanning-tree forward-time 18 cata2924_01# 02:52:07: %SYS-5-CONFIG_I: Configured from console by consolesho spa cata2924_01#sho spanning-tree Spanning tree 1 is executing the IEEE compatible Spanning Tree protocol Bridge Identifier has priority 32768, address 0004.2xxx.0ec0 Configured hello time 2, max age 20, forward delay 18 Current root has priority 32768, address 0003.fxxx.8580 Root port is 14, cost of root path is 19 Topology change flag not set, detected flag not set, changes 20 Times: hold 1, topology change 35, notification 2 hello 2, max age 20, forward delay 15 Timers: hello 0, topology change 0, notification 02箇所あるforward delayのうち、Configuredで始まる行の方だけが、変更した値になっている。それではまた先ほどのようにケーブルを抜き差ししてみよう。
cata2924_01# 02:54:17: %LINK-3-UPDOWN: Interface FastEthernet0/10, changed state to down 02:54:17: ST: sent Topology Change Notice on FastEthernet0/2 vlan 1 02:54:17: ST: FastEthernet0/10 vlan 1 -> blocking 02:54:18: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/10, changed state to down 02:54:23: %LINK-3-UPDOWN: Interface FastEthernet0/10, changed state to up 02:54:23: ST: FastEthernet0/10 vlan 1 -> listening 02:54:24: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/10, changed state to up 02:54:38: ST: FastEthernet0/10 vlan 1 -> learning 02:54:53: ST: sent Topology Change Notice on FastEthernet0/2 vlan 1 02:54:53: ST: FastEthernet0/10 vlan 1 -> forwarding各stateの間隔は15秒のままである。他のスイッチのshow spanning-treeの結果をみても、15秒のままになっている。timerの値はrootで変更しなければ反映しない。
cata2924_02#conf t Enter configuration commands, one per line. End with CNTL/Z. cata2924_02(config)#spanning-tree forward-time 18 cata2924_02(config)#end cata2924_02#sho spanning-tree Spanning tree 1 is executing the IEEE compatible Spanning Tree protocol Bridge Identifier has priority 32768, address 0003.fxxx.8580 Configured hello time 2, max age 20, forward delay 18 We are the root of the spanning tree Topology change flag not set, detected flag not set, changes 20 Times: hold 1, topology change 38, notification 2 hello 2, max age 20, forward delay 18 Timers: hello 0, topology change 0, notification 0forward delayの変更が反映された。 他のスイッチでもConfiguredのところは各自のconfigのままで、 下のほうにある値に反映されている。
cata2924_01#sho spanning-tree Spanning tree 1 is executing the IEEE compatible Spanning Tree protocol Bridge Identifier has priority 32768, address 0004.2xxx.0ec0 Configured hello time 2, max age 20, forward delay 15 Current root has priority 32768, address 0003.fxxx.8580 Root port is 14, cost of root path is 19 Topology change flag not set, detected flag not set, changes 22 Times: hold 1, topology change 35, notification 2 hello 2, max age 20, forward delay 18 Timers: hello 0, topology change 0, notification 0 cata2912_01#sho spanning-tree Spanning tree 1 is executing the IEEE compatible Spanning Tree protocol Bridge Identifier has priority 32768, address 0004.9xxx.23c0 Configured hello time 2, max age 20, forward delay 15 Current root has priority 32768, address 0003.fe67.8580 Root port is 18, cost of root path is 19 Topology change flag not set, detected flag not set, changes 20 Times: hold 1, topology change 35, notification 2 hello 2, max age 20, forward delay 18 Timers: hello 0, topology change 0, notification 0もう一度ケーブルの抜き差しをしてみると
cata2924_01# 03:05:10: %LINK-3-UPDOWN: Interface FastEthernet0/10, changed state to down 03:05:10: ST: sent Topology Change Notice on FastEthernet0/2 vlan 1 03:05:10: ST: FastEthernet0/10 vlan 1 -> blocking 03:05:11: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/10, changed state to down 03:05:14: %LINK-3-UPDOWN: Interface FastEthernet0/10, changed state to up 03:05:14: ST: FastEthernet0/10 vlan 1 -> listening 03:05:15: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/10, changed state to up 03:05:32: ST: FastEthernet0/10 vlan 1 -> learning 03:05:51: ST: sent Topology Change Notice on FastEthernet0/2 vlan 1 03:05:51: ST: FastEthernet0/10 vlan 1 -> forwarding各stateの間隔が18秒になった。 timer値を変える場合はrootで変えなければならない。 ただし、むやみに変えるのはよくないそうです。