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