STP port type network - no bridge assurance!

Hi,

I came across something I though t rather odd the other day.  A config on a nexus 7000 has 'no spanning-tree bridge assurance' configured, but at the same time, on the 802.1q trunks, I saw 'spanning-tree port type network'.

Now it is my understanding that these two go hand in hand?  i.e. spanning-tree port type network 'NEEDS' STP bridge assurance to be on.  Clearly this is not the case, so I am just wondering what the outcome of this will be.  Do the ports fall back to standard STP (effectively port type normal) or could this potentially be a bigger problem if a looped l2 environment were to come into existence?

Unfortunately I didn't have time to re-configure.....

Thanks

Dominic

Comments

  • I have a feeling they will effectively run as STP port type normal.  The only difference between normal and network is bridge assurance, so if you disable BA globally then they are effectively the same.

     

    Brian McGahan, CCIE #8593 (R&S/SP/Security), CCDE #2013::13

    [email protected]

     

    Internetwork Expert, Inc.

    http://www.INE.com

     

    From: [email protected] [mailto:[email protected]] On Behalf Of Dominic_Foley
    Sent: Friday, June 07, 2013 5:07 AM
    To: Brian McGahan
    Subject: [CCIE DC] STP port type network - no bridge assurance!

     

    Hi,

    I came across something I though t rather odd the other day.  A config on a nexus 7000 has 'no spanning-tree bridge assurance' configured, but at the same time, on the 802.1q trunks, I saw 'spanning-tree port type network'.

    Now it is my understanding that these two go hand in hand?  i.e. spanning-tree port type network 'NEEDS' STP bridge assurance to be on.  Clearly this is not the case, so I am just wondering what the outcome of this will be.  Do the ports fall back to standard STP (effectively port type normal) or could this potentially be a bigger problem if a looped l2 environment were to come into existence?

    Unfortunately I didn't have time to re-configure.....

    Thanks

    Dominic




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  • It happens what Brian said:

    N7K-1# sh spanning-tree

    VLAN0001
      Spanning tree enabled protocol rstp
      Root ID    Priority    32769
                 Address     0050.569f.0025
                 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     0050.569f.0025
                 Hello Time  2  sec  Max Age 20 sec  Forward Delay 15 sec

    Interface        Role Sts Cost      Prio.Nbr Type
    ---------------- ---- --- --------- -------- --------------------------------
    Eth2/1           Desg FWD 4         128.257  Network P2p

    N7K-1#
    N7K-1# sh spanning-tree interface e2/1 detail

     Port 257 (Ethernet2/1) of VLAN0001 is designated forwarding
       Port path cost 4, Port priority 128, Port Identifier 128.257
       Designated root has priority 32769, address 0050.569f.0025
       Designated bridge has priority 32769, address 0050.569f.0025
       Designated port id is 128.257, designated path cost 0
       Timers: message age 0, forward delay 0, hold 0
       Number of transitions to forwarding state: 0
       The port type is network
       Link type is point-to-point by default
       BPDU: sent 101, received 0

    N7K-1#

    N7K-2# show spanning-tree

    VLAN0001
      Spanning tree enabled protocol rstp
      Root ID    Priority    32769
                 Address     0050.569f.0025
                 Cost        4
                 Port        257 (Ethernet2/1)
                 Hello Time  2  sec  Max Age 20 sec  Forward Delay 15 sec

      Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
                 Address     0050.569f.0035
                 Hello Time  2  sec  Max Age 20 sec  Forward Delay 15 sec

    Interface        Role Sts Cost      Prio.Nbr Type
    ---------------- ---- --- --------- -------- --------------------------------
    Eth2/1           Root FWD 4         128.257  Network P2p

    N7K-2#
    N7K-2#
    N7K-2# show spanning-tree interface e2/1 detail

     Port 257 (Ethernet2/1) of VLAN0001 is root forwarding
       Port path cost 4, Port priority 128, Port Identifier 128.257
       Designated root has priority 32769, address 0050.569f.0025
       Designated bridge has priority 32769, address 0050.569f.0025
       Designated port id is 128.257, designated path cost 0
       Timers: message age 17, forward delay 0, hold 0
       Number of transitions to forwarding state: 0
       The port type is network
       Link type is point-to-point by default
       BPDU: sent 0, received 97

    N7K-2#

    Antonio Soares, CCIE #18473 (RS/SP/DC)
    [email protected]
    http://www.ccie18473.net

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