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Spanning-Tree Protocol Root Guard

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REFERENCE

Configuring Optional Spanning-Tree Features

MEMO

Switch(config-if)#spanning-tree guard root
  • UplinkFastを入れたSWに設定してはいけない
  • DPがRPになるような計算が起きると、root inconsistant

出力確認

SW1 Priority 0
SW2 Priority 4096

[SW2] RootBridge
                        /  |
                       /   |
                      /    |
           (Fa1/0/2) /     | (Fa1/0/1)
                    /      |
                   /       |
                  /        |
   【SW1】-----[SW4]------[SW3]
     (Fa1/0/24)   (Fa1/0/3)

 

  • SW1をイレギュラーな接続と想定
SW4#sh spa v 1

VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    4097
             Address     001a.6dbc.4a00
             Cost        19
             Port        4 (FastEthernet1/0/2)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     0014.f2a8.4800
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  300 sec

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa1/0/2             Root FWD 19        128.4    P2p
Fa1/0/3             Altn BLK 19        128.5    P2p


SW4#
*Mar  1 00:28:34.606: set portid: VLAN0001 Fa1/0/24: new port id 801A
*Mar  1 00:28:34.606: STP: VLAN0001 Fa1/0/24 -> listening
SW4#
*Mar  1 00:28:36.611: %LINK-3-UPDOWN: Interface FastEthernet1/0/24, changed state to up
SW4#
*Mar  1 00:28:38.607: set portid: VLAN0001 Fa1/0/24: new port id 801A
*Mar  1 00:28:38.607: STP: VLAN0001 Fa1/0/24 -> listening
*Mar  1 00:28:39.597: STP: VLAN0001 heard root     1-0009.e8c2.7000 on Fa1/0/24
*Mar  1 00:28:39.597:     supersedes  4097-001a.6dbc.4a00
*Mar  1 00:28:39.597: %SPANTREE-2-ROOTGUARD_BLOCK: Root guard blocking port FastEthernet1/0/24 on VLAN0001.
*Mar  1 00:28:39.597: STP: VLAN0001 Fa1/0/24 -> blocking
SW4#
*Mar  1 00:28:39.614: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet1/0/24, changed state to up
SW4#
*Mar  1 00:28:41.602: STP: VLAN0001 heard root     1-0009.e8c2.7000 on Fa1/0/24
*Mar  1 00:28:41.602:     supersedes  4097-001a.6dbc.4a00
SW4#
*Mar  1 00:28:43.598: STP: VLAN0001 heard root     1-0009.e8c2.7000 on Fa1/0/24
*Mar  1 00:28:43.598:     supersedes  4097-001a.6dbc.4a00
SW4#sh spa v 1

VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    4097
             Address     001a.6dbc.4a00
             Cost        19
             Port        4 (FastEthernet1/0/2)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     0014.f2a8.4800
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  300 sec

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa1/0/2             Root FWD 19        128.4    P2p
Fa1/0/3             Altn BLK 19        128.5    P2p
Fa1/0/24            Desg BKN*19        128.26   P2p *ROOT_Inc


SW4#
*Mar  1 00:28:55.602: STP: VLAN0001 heard root     1-0009.e8c2.7000 on Fa1/0/24
*Mar  1 00:28:55.602:     supersedes  4097-001a.6dbc.4a00
SW4#
*Mar  1 00:29:05.602: STP: VLAN0001 heard root     1-0009.e8c2.7000 on Fa1/0/24
*Mar  1 00:29:05.602:     supersedes  4097-001a.6dbc.4a00
SW4#
*Mar  1 00:29:08.085: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet1/0/24, changed state to down
SW4#
*Mar  1 00:29:09.100: %LINK-3-UPDOWN: Interface FastEthernet1/0/24, changed state to down
SW4#sh spa v 1

VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    4097
             Address     001a.6dbc.4a00
             Cost        19
             Port        4 (FastEthernet1/0/2)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     0014.f2a8.4800
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  300 sec

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa1/0/2             Root FWD 19        128.4    P2p
Fa1/0/3             Altn BLK 19        128.5    P2p

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