Spanning Tree PVST - ISL Links or 802.1Q

Discussion in 'Cisco' started by Amy L., Jul 11, 2004.

  1. Amy L.

    Amy L. Guest

    I am reading where PVST requires ISL (Building Cisco Multilayer
    Switched Networks (Sybex)) in preparation for 642-811. Is this
    information outdated? By some chance are the switches running PVST+
    which indicates multiple STP instances per vlan when using 802.1Q
    trunks?

    I am on a switch (3550) configured for PVST that is connected to
    different 4506's.

    Spanning Tree Config On 3550
    "spanning-tree mode pvst"

    All of my trunk links are encapsulated with 802.1Q

    (Sample Config For a 3550)
    interface GigabitEthernet0/1
    description Trunk Link to LAB-COREA port G2/6
    switchport trunk encapsulation dot1q
    switchport trunk pruning vlan none
    switchport mode trunk
    end
    <same config on g0/2 except going to LAB-COREB>

    For my VLAN configuration I have it setup for traffic to go across
    different links.

    VLAN0001
    Spanning tree enabled protocol ieee
    Root ID Priority 24577
    Address 000f.244a.3780
    Cost 3004
    Port 49 (GigabitEthernet0/1)
    Hello Time 2 sec Max Age 10 sec Forward Delay 7 sec

    Bridge ID Priority 49153 (priority 49152 sys-id-ext 1)
    Address 000f.2475.4780
    Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
    Aging Time 300
    Uplinkfast enabled

    Interface Role Sts Cost Prio.Nbr Type
    ---------------- ---- --- --------- --------
    --------------------------------
    Gi0/1 Root FWD 3004 128.49 P2p
    Gi0/2 Altn BLK 3004 128.50 P2p

    LAN0087
    Spanning tree enabled protocol ieee
    Root ID Priority 24663
    Address 000f.244a.3800
    Cost 3004
    Port 50 (GigabitEthernet0/2)
    Hello Time 2 sec Max Age 10 sec Forward Delay 7 sec

    Bridge ID Priority 49239 (priority 49152 sys-id-ext 87)
    Address 000f.2475.4780
    Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
    Aging Time 300
    Uplinkfast enabled

    Interface Role Sts Cost Prio.Nbr Type
    ---------------- ---- --- --------- --------
    --------------------------------
    Gi0/1 Altn BLK 3004 128.49 P2p
    Gi0/2 Root FWD 3004 128.50 P2p

    Thanks,
    Amy
    Amy L., Jul 11, 2004
    #1
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  2. Amy L.

    Kevin Widner Guest

    (Amy L.) wrote in message news:<>...
    > I am reading where PVST requires ISL (Building Cisco Multilayer
    > Switched Networks (Sybex)) in preparation for 642-811. Is this
    > information outdated? By some chance are the switches running PVST+
    > which indicates multiple STP instances per vlan when using 802.1Q
    > trunks?
    >
    > I am on a switch (3550) configured for PVST that is connected to
    > different 4506's.
    >
    > Spanning Tree Config On 3550
    > "spanning-tree mode pvst"
    >
    > All of my trunk links are encapsulated with 802.1Q
    >
    > (Sample Config For a 3550)
    > interface GigabitEthernet0/1
    > description Trunk Link to LAB-COREA port G2/6
    > switchport trunk encapsulation dot1q
    > switchport trunk pruning vlan none
    > switchport mode trunk
    > end
    > <same config on g0/2 except going to LAB-COREB>
    >
    > For my VLAN configuration I have it setup for traffic to go across
    > different links.
    >
    > VLAN0001
    > Spanning tree enabled protocol ieee

    .......
    >
    > Thanks,
    > Amy


    PVST+ can most certainly work over .1q trunks.
    Kevin Widner, Jul 16, 2004
    #2
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  3. Amy L.

    Amy L. Guest

    I'm not sure if my post was clear enough, but I was specifically
    talking about PVST. Hence in the configuration I showed the following
    line "spanning-tree mode pvst".

    I am familar that the purpose of PVST+ was to allow multiple VLAN
    instances to work over .1Q trunks. However, I am seeing multiple vlan
    instances running on switches with PVST over .1Q links.

    Amy.


    (Kevin Widner) wrote in message news:<>...
    > (Amy L.) wrote in message news:<>...
    > > I am reading where PVST requires ISL (Building Cisco Multilayer
    > > Switched Networks (Sybex)) in preparation for 642-811. Is this
    > > information outdated? By some chance are the switches running PVST+
    > > which indicates multiple STP instances per vlan when using 802.1Q
    > > trunks?
    > >
    > > I am on a switch (3550) configured for PVST that is connected to
    > > different 4506's.
    > >
    > > Spanning Tree Config On 3550
    > > "spanning-tree mode pvst"
    > >
    > > All of my trunk links are encapsulated with 802.1Q
    > >
    > > (Sample Config For a 3550)
    > > interface GigabitEthernet0/1
    > > description Trunk Link to LAB-COREA port G2/6
    > > switchport trunk encapsulation dot1q
    > > switchport trunk pruning vlan none
    > > switchport mode trunk
    > > end
    > > <same config on g0/2 except going to LAB-COREB>
    > >
    > > For my VLAN configuration I have it setup for traffic to go across
    > > different links.
    > >
    > > VLAN0001
    > > Spanning tree enabled protocol ieee

    > ......
    > >
    > > Thanks,
    > > Amy

    >
    > PVST+ can most certainly work over .1q trunks.
    Amy L., Jul 17, 2004
    #3
  4. Amy L.

    Steinar Haug Guest

    [Amy L.]

    | I'm not sure if my post was clear enough, but I was specifically
    | talking about PVST. Hence in the configuration I showed the following
    | line "spanning-tree mode pvst".

    Cisco uses this in the configuration *both* for PVST and PVST+.

    Steinar Haug, Nethelp consulting,
    Steinar Haug, Jul 17, 2004
    #4
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