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[EX] VSTP and RPVST+ convergence on native-vlan 1

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Article ID: KB18291 KB Last Updated: 27 Jan 2020Version: 3.0
Summary:

This article provides an understanding of the convergence of EX Switch VSTP and Cisco RPVST+ on native-vlan using Junos OS 10.0Rx version.  Junos 10.2 introduces RSTP configuration with VSTP (see below).

RSTP configuration with VSTP was Introduced in Junos OS Release 10.2 (Release Note Feature from 10.2).

RSTP configuration with VSTP—VSTP and RSTP can now be configured concurrently. When VSTP and RSTP are configured concurrently, the first 253 VLANs are configured with VSTP and the remaining VLANs are configured using RSTP. This feature allows users to overcome a previous restriction that only allowed VSTP to run on up to 253 VLANs while no other spanning-tree protocols could run on the additional VLANs.

Solution:

The Cisco Device with RPVST+ and EX Switch VSTP converge by specifying the native-vlan as VLAN 1. On a native-VLAN Cisco Device with RPVST+ configured sends BPDUs on the global multicast address (01:80:c2:00:00:00) and for all other tagged VLANs it sends it to the (01:cc:cc:cc:cc:cd) multicast address. The EX Switch does not send BPDUs to the (01:80:c2:00:00:00) multicast address on native-VLAN when VSTP is enabled; instead it sends it to the (01:cc:cc:cc:cc:cd) multicast address.

The convergence can be achieved by creating a VLAN 1 on the EX Switch and specifying it as native-vlan under the port mode trunk.

Legacy Switch Configuration:

show interfaces ge-0/0/1
unit 0 {
    family ethernet-switching {
        port-mode trunk;
        vlan {
            members [ 2 3 4 5 ];
        }
        native-vlan-id 1;
    }
}
show protocols
vstp {
    vlan all 

OR

ELS Switch Configuration:

show interfaces ge-0/0/1
native-vlan-id 1;
unit 0 {
    family ethernet-switching {
        interface-mode trunk;
        vlan {
            members 2-5;
        }
    }
}

show protocols
vstp {
    vlan all {
        interface all;
    }
}

Cisco Device Configuration:

interface GigabitEthernet0/1
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1-5
switchport mode trunk

 

VLAN1 was converging:

  • This is because the Cisco device was sending the BPDUs on VLAN 1 as untagged BPDUs. 
  • The catch is RPVST+ was sending the untagged  BPDUs to both (01:80:c2:00:00:00) and (01:cc:cc:cc:cc:cd) multicast address.

Below is a screenshot of the packet capture showing RPVST+ BPDUs to both the multicast address on untagged VLAN:

Sample output EX Switch:

root> show configuration protocols vstp

root> show spanning-tree bridge    | no-more

STP bridge parameters
Context ID                          : 1
Enabled protocol                    : RSTP

STP bridge parameters for VLAN 1
  Root ID                           : 32769.00:23:34:42:cc:00 –Ex shows cisco as the root bridge.
  Root cost                         : 20000
  Root port                         : ge-0/0/1.0
  Hello time                        : 2 seconds
  Maximum age                       : 20 seconds
  Forward delay                     : 15 seconds
  Message age                       : 1
  Number of topology changes        : 1
  Time since last topology change   : 877 seconds
  Topology change initiator         : ge-0/0/1.0
  Local parameters
    Bridge ID                       : 32769.b0:c6:9a:d3:b1:80
    Extended system ID              : 1
    Internal instance ID            : 0

STP bridge parameters
Context ID                          : 2
Enabled protocol                    : RSTP

STP bridge parameters for VLAN 2
  Root ID                           : 32770.00:23:34:42:cc:00
  Root cost                         : 20000
  Root port                         : ge-0/0/1.0
  Hello time                        : 2 seconds
  Maximum age                       : 20 seconds
  Forward delay                     : 15 seconds
  Message age                       : 1
  Number of topology changes        : 1
  Time since last topology change   : 876 seconds
  Topology change initiator         : ge-0/0/1.0
  Topology change last recvd. from  : 00:23:34:42:cc:01
  Local parameters
    Bridge ID                       : 32770.b0:c6:9a:d3:b1:80
    Extended system ID              : 2
    Internal instance ID            : 0

STP bridge parameters
Context ID                          : 3
Enabled protocol                    : RSTP

STP bridge parameters for VLAN 3
  Root ID                           : 32771.00:23:34:42:cc:00
  Root cost                         : 20000
  Root port                         : ge-0/0/1.0
  Hello time                        : 2 seconds
  Maximum age                       : 20 seconds
  Forward delay                     : 15 seconds
  Message age                       : 1
  Number of topology changes        : 1
  Time since last topology change   : 876 seconds
  Topology change initiator         : ge-0/0/1.0
  Topology change last recvd. from  : 00:23:34:42:cc:01
  Local parameters
    Bridge ID                       : 32771.b0:c6:9a:d3:b1:80
    Extended system ID              : 3
    Internal instance ID            : 0

STP bridge parameters
Context ID                          : 4
Enabled protocol                    : RSTP

STP bridge parameters for VLAN 4
  Root ID                           : 32772.00:23:34:42:cc:00
  Root cost                         : 20000
  Root port                         : ge-0/0/1.0
  Hello time                        : 2 seconds
  Maximum age                       : 20 seconds
  Forward delay                     : 15 seconds
  Message age                       : 1
  Number of topology changes        : 1
  Time since last topology change   : 876 seconds
  Topology change initiator         : ge-0/0/1.0
  Topology change last recvd. from  : 00:23:34:42:cc:01
  Local parameters
    Bridge ID                       : 32772.b0:c6:9a:d3:b1:80
    Extended system ID              : 4
    Internal instance ID            : 0

STP bridge parameters
Context ID                          : 5
Enabled protocol                    : RSTP

STP bridge parameters for VLAN 5
  Root ID                           : 32773.00:23:34:42:cc:00
  Root cost                         : 20000
  Root port                         : ge-0/0/1.0
  Hello time                        : 2 seconds
  Maximum age                       : 20 seconds
  Forward delay                     : 15 seconds
  Message age                       : 1
  Number of topology changes        : 1
  Time since last topology change   : 876 seconds
  Topology change initiator         : ge-0/0/1.0
  Topology change last recvd. from  : 00:23:34:42:cc:01
  Local parameters
    Bridge ID                       : 32773.b0:c6:9a:d3:b1:80
    Extended system ID              : 5
    Internal instance ID            : 0

root>
  • The EX Switch and Cisco Device converge on native VLANs by specifying native-vlan on the EX-side. 
  • The Cisco and EX Switch can also converge when specifying any other VLAN as native-vlan. 
  • Cisco Device was sending the untagged BPDUs to both (01:80:c2:00:00:00) and (01:cc:cc:cc:cc:cd) multicast address which is VLAN5.

Cisco Device Configuration with native VLAN 5

VLAN0001

Spanning tree enabled protocol rstp
  Root ID    Priority    32769
             Address     0008.a493.42c0
             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     0008.a493.42c0
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/8            Desg FWD 19        128.8    P2p
Fa0/9            Desg FWD 19        128.9    P2p

VLAN0002

  Spanning tree enabled protocol rstp
  Root ID    Priority    4098
             Address     0021.59cf.3500
             Cost        19
             Port        8 (FastEthernet0/8)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32770  (priority 32768 sys-id-ext 2)
             Address     0008.a493.42c0
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/8            Root FWD 19        128.8    P2p
Fa0/9            Altn BLK 19        128.9    P2p

VLAN0003

  Spanning tree enabled protocol rstp
  Root ID    Priority    32771
             Address     0008.a493.42c0
             This bridge is the root
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32771  (priority 32768 sys-id-ext 3)
             Address     0008.a493.42c0
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/8            Desg FWD 19        128.8    P2p
Fa0/9            Desg FWD 19        128.9    P2p

VLAN0005

  Spanning tree enabled protocol rstp
  Root ID    Priority    32773
             Address     0008.a493.42c0
             This bridge is the root
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32773  (priority 32768 sys-id-ext 5)
             Address     0008.a493.42c0
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/8            Desg FWD 19        128.8    P2p
Fa0/9            Desg FWD 19        128.9    P2p

 


NOTE: The Cisco IOS version used for testing is 12.2(50)SE 3.

If the EX Switch is the root bridge for native-vlan then the Cisco Device is not able to converge.  Cisco accepts BPDUs only from  (01:80:c2:00:00:00) on the native-vlan.

Cisco Device:

#show spanning-tree vlan 1

VLAN0001

  Spanning tree enabled protocol rstp
  Root ID    Priority    32769
             Address     0023.3442.cc00
             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     0023.3442.cc00
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  300 sec

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi0/1               Desg FWD 4         128.1    P2p
Gi0/2               Desg FWD 4         128.2    P2p


NOTE: If the Cisco is the root bridge, it will converge on native-vlan without using Junos 10.2 versions.

Modification History:

2020-01-27: Updated legacy switch and added ELS switch configuration

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