Description

This article provides an understanding of the convergence of Juniper Networks EX Series Switches VSTP and Cisco RPVST+ on native-vlan using Junos OS.

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


 

Solution

The following restrictions apply to VSTP:
 

  • The EX Series switches EX4300, EX4600 and the QFX platforms QFX5100,QFX3500,QFX3600 support 510 Vlans on VSTP.

  • On EX Series (except EX9200) and QFX Series switches running Junos OS that supports ELS—VSTP can support up to 510 VLANs.

  • On EX9200 switches—VSTP can support up to 4000 VLANs.

  • On an EX Series switch running Junos OS that does not support ELS—VSTP can support up to 253 VLANs.

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 (01:00:0c: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 (01:00:0c: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 (01:00:0c:cc:cc:cd) multicast address.

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

alt
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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 the native VLAN 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 (01:00:0c: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
2022-09-28: Updated VSTP limitations, article is still relevant and valid.

2025-10-29: Correcting destination mac