Published 6月 07, 2018 by with 0 comment

CCNP-BCMSN-v5.0 Lab 3-2: Modifying Default Spanning Tree Behavior


!!!I use real Cisco 3550 switch *4 to do this lab. I do not use Dynamips to do this lab.!!!

Objective:
The purpose of this lab is to observe what happens when the default spanning tree behavior is modified.

Scenario:
In this lab, you will see what happens when the default spanning tree behavior is modified.


Basic Configuration:
DLS(1-2) & ALS(1-2):
enable
configure terminal
!
no ip domain lookup
!
line console 0
 logging synchronous
 exec-timeout 0 0
!
hostname


Step 1
Start by deleting the vlan.dat file, erasing the startup config, and reloading all your switches.
All Switch:
Clearing all Switches


Step 2
Use the "show spanning-tree" command to check how your nonconfigured
switches created a spanning tree. Verify which switch became
the root bridge. In the topology used in this lab, DLS1 is the root bridge.
DLS1:
DSL1#show spanning-tree

VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    32769
             Address     000e.d7a6.9c80
             This bridge is the root
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     000e.d7a6.9c80
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/7               Desg FWD 19        128.7    P2p
Fa0/8               Desg FWD 19        128.8    P2p
Fa0/9               Desg FWD 19        128.9    P2p
Fa0/10              Desg FWD 19        128.10   P2p
Fa0/11              Desg FWD 19        128.11   P2p
Fa0/12              Desg FWD 19        128.12   P2p

DSL1#s

DLS2:
DSL2#show spanning-tree

VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    32769
             Address     000e.d7a6.9c80
             Cost        19
             Port        11 (FastEthernet0/11)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     000e.d7a6.ab00
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/7               Desg FWD 19        128.7    P2p
Fa0/8               Desg FWD 19        128.8    P2p
Fa0/9               Desg FWD 19        128.9    P2p
Fa0/10              Desg FWD 19        128.10   P2p
Fa0/11              Root FWD 19        128.11   P2p
Fa0/12              Altn BLK 19        128.12   P2p

DSL2#

ALS1:
ASL1#show spanning-tree

VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    32769
             Address     000e.d7a6.9c80
             Cost        19
             Port        7 (FastEthernet0/7)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     000e.d7a6.c500
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/7               Root FWD 19        128.7    P2p
Fa0/8               Altn BLK 19        128.8    P2p
Fa0/9               Altn BLK 19        128.9    P2p
Fa0/10              Altn BLK 19        128.10   P2p
Fa0/11              Desg FWD 19        128.11   P2p
Fa0/12              Desg FWD 19        128.12   P2p

ASL1#

ALS2:
ASL2#show spanning-tree

VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    32769
             Address     000e.d7a6.9c80
             Cost        19
             Port        9 (FastEthernet0/9)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     000e.d7d4.7500
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/7               Altn BLK 19        128.7    P2p
Fa0/8               Altn BLK 19        128.8    P2p
Fa0/9               Root FWD 19        128.9    P2p
Fa0/10              Altn BLK 19        128.10   P2p
Fa0/11              Altn BLK 19        128.11   P2p
Fa0/12              Altn BLK 19        128.12   P2p

ASL2#


Step 3
Because DLS1 is the root switch in this topology, we
change DLS2 to the primary root and ALS1 to the secondary.
First, debug DLS1:
DSL1:
DSL1#debug spanning-tree events

Then change DLS2 to the primary root:
DSL2(config)#spanning-tree vlan 1 root primary

Then change ALS1 to the secondary root:
ASL1(config)#spanning-tree vlan 1 root secondary

You can see the topology changes on the switch that you enabled
debugging on.
DSL1#debug spanning-tree events
Spanning Tree event debugging is on
*Mar  1 00:10:12.519: STP: VLAN0001 heard root 24577-000e.d7a6.ab00 on Fa0/11
*Mar  1 00:10:12.519:     supersedes 32769-000e.d7a6.9c80
*Mar  1 00:10:12.519: STP: VLAN0001 new root is 24577, 000e.d7a6.ab00 on port Fa0/11, cost 19
*Mar  1 00:10:12.523: STP: VLAN0001 sent Topology Change Notice on Fa0/11
*Mar  1 00:10:12.523: STP: VLAN0001 Fa0/12 -> blocking
*Mar  1 00:10:56.523: STP: VLAN0001 sent Topology Change Notice on Fa0/11
*Mar  1 00:10:56.523: STP: VLAN0001 Fa0/7 -> blocking
*Mar  1 00:10:56.523: STP: VLAN0001 Fa0/8 -> blocking
DSL1#

DSL2#show running-config | include spanning-tree vlan 1
spanning-tree vlan 1 priority 24576

ASL1#show running-config | include spanning-tree vlan 1
spanning-tree vlan 1 priority 28672

DSL1#show spanning-tree

VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    24577
             Address     000e.d7a6.ab00
             Cost        19
             Port        11 (FastEthernet0/11)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     000e.d7a6.9c80
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/7               Altn BLK 19        128.7    P2p
Fa0/8               Altn BLK 19        128.8    P2p
Fa0/9               Desg FWD 19        128.9    P2p
Fa0/10              Desg FWD 19        128.10   P2p
Fa0/11              Root FWD 19        128.11   P2p
Fa0/12              Altn BLK 19        128.12   P2p


Step 4
On the link between DLS1 and DLS2, the default forwarding port is
f0/11 because it is lower, and the default blocking port is
f0/12 because it is higher. The two ports have equal costs because they
are the same speed. We will look into modifying this later.
DLS1:
DSL1#show spanning-tree

VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    24577
             Address     000e.d7a6.ab00
             Cost        19
             Port        11 (FastEthernet0/11)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     000e.d7a6.9c80
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/7               Altn BLK 19        128.7    P2p
Fa0/8               Altn BLK 19        128.8    P2p
Fa0/9               Desg FWD 19        128.9    P2p
Fa0/10              Desg FWD 19        128.10   P2p
Fa0/11              Root FWD 19        128.11   P2p
Fa0/12              Altn BLK 19        128.12   P2p

DSL1#


Port priorities range from 0 to 240, in increments of 16. The default priority
is 128, and a lower priority is preferred
DSL2(config)#interface fastEthernet 0/12
DSL2(config-if)#spanning-tree port-priority 112
DSL2#show spanning-tree

VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    24577
             Address     000e.d7a6.ab00
             This bridge is the root
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    24577  (priority 24576 sys-id-ext 1)
             Address     000e.d7a6.ab00
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/7               Desg FWD 19        128.7    P2p
Fa0/8               Desg FWD 19        128.8    P2p
Fa0/9               Desg FWD 19        128.9    P2p
Fa0/10              Desg FWD 19        128.10   P2p
Fa0/11              Desg FWD 19        128.11   P2p
Fa0/12              Desg FWD 19        112.12   P2p

DSL2#

DSL1#show spanning-tree

VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    24577
             Address     000e.d7a6.ab00
             Cost        19
             Port        12 (FastEthernet0/12)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     000e.d7a6.9c80
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/7               Altn BLK 19        128.7    P2p
Fa0/8               Altn BLK 19        128.8    P2p
Fa0/9               Desg FWD 19        128.9    P2p
Fa0/10              Desg FWD 19        128.10   P2p
Fa0/11              Altn BLK 19        128.11   P2p
Fa0/12              Root FWD 19        128.12   P2p

DSL1#


Step 5
Portfast allows you to bypass the normal phases of spanning tree
and move a port to the forwarding state as soon as it is turned on.
ASL1(config)#interface fastEthernet 0/6
ASL1(config-if)#switchport mode access
ASL1(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 bridging loops.
 Use with CAUTION

%Portfast has been configured on FastEthernet0/6 but will only
 have effect when the interface is in a non-trunking mode.
ASL1(config-if)#


Step 6
For this scenario, I am changing the cost of ports f0/11 and 12 on ALS1 and ALS2.
ASL1#show spanning-tree

VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    24577
             Address     000e.d7a6.ab00
             Cost        19
             Port        9 (FastEthernet0/9)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    28673  (priority 28672 sys-id-ext 1)
             Address     000e.d7a6.c500
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/7               Desg FWD 19        128.7    P2p
Fa0/8               Desg FWD 19        128.8    P2p
Fa0/9               Root FWD 19        128.9    P2p
Fa0/10              Altn BLK 19        128.10   P2p
Fa0/11              Desg FWD 19        128.11   P2p
Fa0/12              Desg FWD 19        128.12   P2p

ASL1#

ASL2#show spanning-tree

VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    24577
             Address     000e.d7a6.ab00
             Cost        19
             Port        7 (FastEthernet0/7)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     000e.d7d4.7500
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/7               Root FWD 19        128.7    P2p
Fa0/8               Altn BLK 19        128.8    P2p
Fa0/9               Altn BLK 19        128.9    P2p
Fa0/10              Altn BLK 19        128.10   P2p
Fa0/11              Altn BLK 19        128.11   P2p
Fa0/12              Altn BLK 19        128.12   P2p

ASL2#

Now, change the port cost to 10 on both ALS1 and ALS2:
ASL1(config)#interface range fastEthernet 0/11 - 12
ASL1(config-if-range)#spanning-tree cost 10

ASL2(config)#interface range fastEthernet 0/11 - 12
ASL2(config-if-range)#spanning-tree cost 10

ASL1#show spanning-tree

VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    24577
             Address     000e.d7a6.ab00
             Cost        19
             Port        9 (FastEthernet0/9)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    28673  (priority 28672 sys-id-ext 1)
             Address     000e.d7a6.c500
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/7               Desg FWD 19        128.7    P2p
Fa0/8               Desg FWD 19        128.8    P2p
Fa0/9               Root FWD 19        128.9    P2p
Fa0/10              Altn BLK 19        128.10   P2p
Fa0/11              Desg FWD 10        128.11   P2p
Fa0/12              Desg FWD 10        128.12   P2p

ASL1#

ASL2#show spanning-tree

VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    24577
             Address     000e.d7a6.ab00
             Cost        19
             Port        7 (FastEthernet0/7)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     000e.d7d4.7500
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/7               Root FWD 19        128.7    P2p
Fa0/8               Altn BLK 19        128.8    P2p
Fa0/9               Altn BLK 19        128.9    P2p
Fa0/10              Altn BLK 19        128.10   P2p
Fa0/11              Altn BLK 10        128.11   P2p
Fa0/12              Altn BLK 10        128.12   P2p

ASL2#


Final Configurations
DLS1:
hostname DSL1
!
no ip domain-lookup
!
line con 0
 exec-timeout 0 0
 logging synchronous
!
end

DLS2:
hostname DSL2
!
no ip domain-lookup
!
spanning-tree vlan 1 priority 24576
!
line con 0
 exec-timeout 0 0
 logging synchronous
!
end

ALS1:
hostname ASL1
!
no ip domain-lookup
!
spanning-tree vlan 1 priority 28672
!
interface FastEthernet0/6
 switchport mode access
 spanning-tree portfast
!
interface FastEthernet0/11
 spanning-tree cost 10
!
interface FastEthernet0/12
 spanning-tree cost 10
!
line con 0
 exec-timeout 0 0
 logging synchronous
!
end

ALS2:
hostname ASL2
!
no ip domain-lookup
!
interface FastEthernet0/11
 spanning-tree cost 10
!
interface FastEthernet0/12
 spanning-tree cost 10
!
line con 0
 exec-timeout 0 0
 logging synchronous
!
end


Reference:
Cisco Networking Academy
http://www.cisco.com/web/learning/netacad/index.html

CCNP Version 5.0: Building Multilayer Switched Networks
Student Lab Manual


最初發表 / 最後更新: 2008.10.06 / 2018.06.07

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