Friday, June 5, 2015

Securing Spanning Tree Protocol (STP)

We normally use Rapid PVST+ (RPVST+) on a client site and MST for our data center core. It's important to secure STP/Layer 2 since this is where LAN users connects to the network. It's also wise to manually configure the primary and secondary root switch in STP to make troubleshooting easier.


DLS1#show spanning-tree vlan 1

VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    32769  
             Address     0016.c756.6180
             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     0016.c756.6180
             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        128.9    P2p
Fa0/8               Desg FWD 19        128.10   P2p
Fa0/9               Desg FWD 19        128.11   P2p
Fa0/10              Desg FWD 19        128.12   P2p
Fa0/11              Desg FWD 19        128.13   P2p
Fa0/12              Desg FWD 19        128.14   P2p

DLS1(config)#spanning-tree vlan 1,100 root primary   // FOR ROOT BRIDGE TO BE PREDICTABLE AND OPTIMIZED PATHS FOR LAYER 2
DLS1(config)#spanning-tree vlan 200 root secondary


DLS2(config)#spanning-tree vlan 1,100 root secondary
DLS2(config)#spanning-tree vlan 200 root primary


DLS1#show spanning-tree

VLAN0001  
  Spanning tree enabled protocol ieee
  Root ID    Priority    24577   
             Address     0016.c756.6180
             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     0016.c756.6180
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 15

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/7               Desg FWD 19        128.9    P2p
Fa0/8               Desg FWD 19        128.10   P2p
Fa0/9               Desg FWD 19        128.11   P2p
Fa0/10              Desg FWD 19        128.12   P2p
Fa0/11              Desg FWD 19        128.13   P2p
Fa0/12              Desg FWD 19        128.14   P2p


VLAN0100  
  Spanning tree enabled protocol ieee
  Root ID    Priority    24676  
             Address     0016.c756.6180
             This bridge is the root  
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    24676  (priority 24576 sys-id-ext 100)
             Address     0016.c756.6180
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 15

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/7               Desg FWD 19        128.9    P2p
Fa0/8               Desg FWD 19        128.10   P2p
Fa0/9               Desg FWD 19        128.11   P2p
Fa0/10              Desg FWD 19        128.12   P2p
Fa0/11              Desg FWD 19        128.13   P2p
Fa0/12              Desg FWD 19        128.14   P2p

 
VLAN0200  
  Spanning tree enabled protocol ieee
  Root ID    Priority    24776  
             Address     0016.c840.3580     // DLS2 MAC ADDRESS
             Cost        19
             Port        13 (FastEthernet0/11)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    28872  (priority 28672 sys-id-ext 200)
             Address     0016.c756.6180
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 15

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/7               Desg FWD 19        128.9    P2p
Fa0/8               Desg FWD 19        128.10   P2p
Fa0/9               Desg FWD 19        128.11   P2p
Fa0/10              Desg FWD 19        128.12   P2p
Fa0/11              Root FWD 19        128.13   P2p
Fa0/12              Altn BLK 19        128.14   P2p


DLS2#show spanning-tree

VLAN0001  
  Spanning tree enabled protocol ieee
  Root ID    Priority    24577  
             Address     0016.c756.6180     // DLS1 MAC ADDRESS
             Cost        19
             Port        13 (FastEthernet0/11)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    28673  (priority 28672 sys-id-ext 1)
             Address     0016.c840.3580
             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        128.9    P2p
Fa0/8               Desg FWD 19        128.10   P2p
Fa0/9               Desg FWD 19        128.11   P2p
Fa0/10              Desg FWD 19        128.12   P2p
Fa0/11              Root FWD 19        128.13   P2p
Fa0/12              Altn BLK 19        128.14   P2p


VLAN0100  
  Spanning tree enabled protocol ieee
  Root ID    Priority    24676   
             Address     0016.c756.6180  
             Cost        19
             Port        13 (FastEthernet0/11)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    28772  (priority 28672 sys-id-ext 100)
             Address     0016.c840.3580
             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        128.9    P2p
Fa0/8               Desg FWD 19        128.10   P2p
Fa0/9               Desg FWD 19        128.11   P2p
Fa0/10              Desg FWD 19        128.12   P2p
Fa0/11              Root FWD 19        128.13   P2p
Fa0/12              Altn BLK 19        128.14   P2p


VLAN0200   
  Spanning tree enabled protocol ieee
  Root ID    Priority    24776   
             Address     0016.c840.3580    
             This bridge is the root   
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    24776  (priority 24576 sys-id-ext 200)
             Address     0016.c840.3580
             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        128.9    P2p
Fa0/8               Desg FWD 19        128.10   P2p
Fa0/9               Desg FWD 19        128.11   P2p
Fa0/10              Desg FWD 19        128.12   P2p
Fa0/11              Desg FWD 19        128.13   P2p
Fa0/12              Desg FWD 19        128.14   P2p


DLS2#show spanning-tree

VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    24577
             Address     0016.c756.6180
             Cost        19
             Port        13 (FastEthernet0/11)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    28673  (priority 28672 sys-id-ext 1)
             Address     0016.c840.3580
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 15

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/7               Desg FWD 19        128.9    P2p
Fa0/8               Desg FWD 19        128.10   P2p
Fa0/9               Desg FWD 19        128.11   P2p
Fa0/10              Desg FWD 19        128.12   P2p
Fa0/11              Root FWD 19        128.13   P2p   
Fa0/12              Altn BLK 19        128.14   P2p


DLS2(config)#interface fastethernet0/11
DLS2(config-if)#spanning-tree ?
  bpdufilter     Don't send or receive BPDUs on this interface
  bpduguard      Don't accept BPDUs on this interface
  cost           Change an interface's spanning tree port path cost
  guard          Change an interface's spanning tree guard mode
  link-type      Specify a link type for spanning tree protocol use
  mst            Multiple spanning tree
  port-priority  Change an interface's spanning tree port priority
  portfast       Enable an interface to move directly to forwarding on link up
  stack-port     Enable stack port
  vlan           VLAN Switch Spanning Tree

DLS2(config-if)#spanning-tree guard ?
  loop  Set guard mode to loop guard on interface
  none  Set guard mode to none
  root  Set guard mode to root guard on interface

DLS2(config-if)#spanning-tree guard root    // MAKES A PORT root-inconsistent IF A SWITCH IS CONNECTED WITH LOWER BID THAN ROOT BRIDGE
DLS2(config-if)#
*Mar  1 01:52:33.223: %SPANTREE-2-ROOTGUARD_CONFIG_CHANGE: Root guard enabled on port

FastEthernet0/11.
*Mar  1 01:52:34.230: %SPANTREE-2-ROOTGUARD_BLOCK: Root guard blocking port FastEthernet0/11 on

VLAN0100.

DLS2#show spanning-tree ?
  WORD               bridge group list, example 1,3-5,7,9
  active             Report on active interfaces only
  backbonefast       Show spanning tree backbonefast status
  blockedports       Show blocked ports
  bridge             Status and configuration of this bridge
  detail             Detailed information
  inconsistentports  Show inconsistent ports
  interface          Spanning Tree interface status and configuration
  mst                Multiple spanning trees
  pathcost           Show Spanning pathcost options
  root               Status and configuration of the root bridge
  summary            Summary of port states
  uplinkfast         Show spanning tree uplinkfast status
  vlan               VLAN Switch Spanning Trees
  |                  Output modifiers
  <cr>

DLS2#show spanning-tree inconsistentports

Name                 Interface                Inconsistency
-------------------- ------------------------ ------------------
VLAN0001             FastEthernet0/11         Root Inconsistent
VLAN0100             FastEthernet0/11         Root Inconsistent

Number of inconsistent ports (segments) in the system : 2


ALS1(config)#spanning-tree ?
  backbonefast  Enable BackboneFast Feature
  etherchannel  Spanning tree etherchannel specific configuration
  extend        Spanning Tree 802.1t extensions
  logging       Enable Spanning tree logging
  loopguard     Spanning tree loopguard options
  mode          Spanning tree operating mode
  mst           Multiple spanning tree configuration
  pathcost      Spanning tree pathcost options
  portfast      Spanning tree portfast options
  transmit      STP transmit parameters
  uplinkfast    Enable UplinkFast Feature
  vlan          VLAN Switch Spanning Tree

ALS1(config)#spanning-tree portfast ?
  bpdufilter  Enable portfast bdpu filter on this switch
  bpduguard   Enable portfast bpdu guard on this switch
  default     Enable portfast by default on all access ports

ALS1(config)#spanning-tree portfast bpduguard ?
  default  Enable bdpu guard by default on all portfast ports

ALS1(config)#spanning-tree portfast bpduguard default    // MAKES AN ACCESS PORT error-disable IF IT

RECEIVES BPDUs
ALS1(config)#do show spanning-tree summary
Switch is in pvst mode
Root bridge for: none
Extended system ID           is enabled
Portfast Default             is disabled
PortFast BPDU Guard Default  is enabled   
Portfast BPDU Filter Default is disabled
Loopguard Default            is disabled
EtherChannel misconfig guard is enabled
UplinkFast                   is disabled
BackboneFast                 is disabled
Configured Pathcost method used is short

Name                   Blocking Listening Learning Forwarding STP Active
---------------------- -------- --------- -------- ---------- ----------
VLAN0001                     5         0        0          1          6
VLAN0100                     5         0        0          1          6
VLAN0200                     5         0        0          1          6
---------------------- -------- --------- -------- ---------- ----------
3 vlans                     15         0        0          3         18

ALS1#show run interface fastethernet0/6
Building configuration...

Current configuration : 109 bytes
!
interface FastEthernet0/6
 switchport access vlan 100
 switchport mode access
 spanning-tree portfast
end


02:04:17: %LINK-3-UPDOWN: Interface FastEthernet0/6, changed state to up
02:04:18: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/6, changed state to up
02:04:18: %SPANTREE-2-BLOCK_BPDUGUARD: Received BPDU on port FastEthernet0/6 with BPDU Guard enabled. Disabling port.
02:04:18: %PM-4-ERR_DISABLE: bpduguard error detected on Fa0/6, putting Fa0/6 in err-disable state
02:04:19: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/6, changed state to down
02:04:20: %LINK-3-UPDOWN: Interface FastEthernet0/6, changed state to down
ALS1#show interface fastethernet0/6
FastEthernet0/6 is down, line protocol is down (err-disabled)  
  Hardware is Fast Ethernet, address is 6416.8dec.a707 (bia 6416.8dec.a707)
  MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Auto-duplex, Auto-speed, media type is 10/100BaseTX
  input flow-control is off, output flow-control is unsupported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:16, output 00:00:16, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     6125 packets input, 1320320 bytes, 0 no buffer
     Received 6040 broadcasts (0 multicasts)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 4134 multicast, 0 pause input
     0 input packets with dribble condition detected
     3788 packets output, 269527 bytes, 0 underruns
     0 output errors, 0 collisions, 7 interface resets
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier, 0 PAUSE output
     0 output buffer failures, 0 output buffers swapped out


ALS1(config)#interface fastethernet0/6
ALS1(config-if)#storm-control ?
  action     Action to take for storm-control
  broadcast  Broadcast address storm control
  multicast  Multicast address storm control
  unicast    Unicast address storm control

ALS1(config-if)#storm-control broadcast ?
  level  Set storm suppression level on this interface

ALS1(config-if)#storm-control broadcast level ?
  <0.00 - 100.00>  Enter rising threshold
  bps              Enter suppression level in bits per second
  pps              Enter suppression level in packets per second

ALS1(config-if)#storm-control broadcast level 50    // TO CONTROL BROADCAST STORM ON AN UNMANAGED SWITCH

ALS1#sh run interface fastethernet0/6
Building configuration...

Current configuration : 131 bytes
!
interface FastEthernet0/6
 switchport trunk encapsulation dot1q
 switchport mode trunk
 storm-control broadcast level 50.00
end


DLS1(config)#udld ?
  aggressive  Enable UDLD protocol in aggressive mode on fiber ports except
              where locally configured
  enable      Enable UDLD protocol on fiber ports except where locally
              configured
  message     Set UDLD message parameters

DLS1(config)#udld aggressive    // AGGRESSIVE KEYWORD PUTS A FIBER INTERFACE TO error-disable WHEN A UNIDIRECTIONAL LINK IS DETECTED; LOOP GUARD CAN BE CONFIGURED AS AN ALTERNATIVE; CAN ALSO CONFIGURE BOTH OR ON AN ETHERCHANNEL LINK

DLS1#show udld gigabitethernet0/1

Interface Gi0/1
---
Port enable administrative configuration setting: Follows device default
Port enable operational state: Enabled / in aggressive mode  
Current bidirectional state: Unknown
Current operational state: Link down
Message interval: 7
Time out interval: 5
No neighbor cache information stored

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