Support Support Downloads Knowledge Base Case Manager My Juniper Community

Knowledge Base

Search our Knowledge Base sites to find answers to your questions.

Ask All Knowledge Base Sites All Knowledge Base Sites JunosE Defect (KA)Knowledge BaseSecurity AdvisoriesTechnical BulletinsTechnotes Sign in to display secure content and recently viewed articles

EX-series Switch and MSTP (Multiple Spanning Tree Protocol)

0

0

Article ID: KB11344 KB Last Updated: 30 Apr 2020Version: 4.0
Summary:

The EX-series switch supports Multiple Spanning Tree (MST). The multiple spanning tree was originally defined in the IEEE 802.1s draft and later incorporated into the IEEE 802.1Q-2003 specification.

MST extends the IEEE following rapid spanning tree (RST) algorithm to multiple spanning trees. This extension provides both rapid convergence and load balancing in a VLAN environment.  All common spanning tree environments (CST) contain CST, which is used to interconnect individual MST regions or MST regions with independent RSTP devices. A single root bridge is elected and tasked with path calculation for the CST.

MSTP connects all switches and LANs with single common and internal spanning tree (CIST).

This article explains how to configure MST and debug it on EX Series switches.

 

Solution:

Sample Topology

(EX Switch A) =============== (Ex Switch B)

EX Switch A and B are connected by 2 interfaces (ge-0/0/22 & ge-0/0/23 on each EX Switch) with multiple VLAN's configured on each switch.


MST Configuration Notes:

  1. Disable RSTP protocol running on the EX switches before activating MSTP.
  2. Default MST instance running on switches will be Instance 0.
  3. Multiple instances of MST can be created on EX switches.


EX Switch A Configuration:

[Edit protocols mstp]
user@switchA# show

Configuration-name test   >>>>> Must Match on participating switches. - User defined configuration name.
revision-level 1;       >>>> Must Match on participating switches.
msti 1 {
bridge-priority 4k;
vlan 1-10;              >>>>  Must Match on participating switches.
}
msti 2 {
bridge-priority 8K;     >>>> MSTP instances defined with individual bridge-priority values and VLAN ranges
vlan 11-20;
}
msti 3
bridge-priority 12k;
vlan 21-30;
}
---------------------------------------------------------------

EX Switch B Configuration:

[Edit protocols mstp]
user@switchA# show
Configuration-name test         >>>>>>>>  Must Match on participating switches. - User defined configuration name.
revision-level 1;               >>>>>>>> Must Match on participating switches.
msti 1 {
bridge-priority 12k;
vlan 1-10;                      >>>>>>>> Must Match on participating switches.
}
msti 2 {
bridge-priority 4K;             >>>>>>>> MSTP instances defined with individual bridge-priority values and VLAN ranges
vlan 11-20;
}
msti 3
bridge-priority 8k;
vlan 21-30;
}
-----------------------------------------------

Verifying MST activity on the EX Switch:

user@switchA# run show spanning-tree mstp configuration
MSTP information
Context identifier     : 0
Region name            : test
Revision               : 10
Configuration digest   : 0x476c7ee38f56eea4a9bbe3fa9e7b7979

MSTI     Member VLANs                                                      
   0 0,31-4094                                                       
   1 1-10                                                            
   2 11-20                                                           
   3 21-30   
[edit protocols mstp]
user@SwitchA# run show spanning-tree bridge 
STP bridge parameters
Context ID                          : 0
Enabled protocol                    : MSTP

STP bridge parameters for CIST
  Root ID                           : 32768.00:19:e2:50:94:a0
  Root cost                         : 20000
  Root port                         : ge-0/0/0.0
  CIST regional root                : 32768.00:19:e2:53:8a:80
  CIST internal root cost           : 0
  Hello time                        : 2 seconds
  Maximum age                       : 20 seconds
  Forward delay                     : 15 seconds
  Hop count                         : 20
  Message age                       : 1
  Number of topology changes        : 13
  Time since last topology change   : 249 seconds
  Local parameters
    Bridge ID                       : 32768.00:19:e2:53:8a:80
    Extended system ID              : 0
    Internal instance ID            : 0

STP bridge parameters for MSTI 1
  MSTI regional root                : 4097.00:19:e2:53:8a:80
  Hello time                        : 2 seconds
  Maximum age                       : 20 seconds
  Forward delay                     : 15 seconds
  Local parameters
    Bridge ID                       : 4097.00:19:e2:53:8a:80
    Extended system ID              : 0
    Internal instance ID            : 1

STP bridge parameters for MSTI 2
  MSTI regional root                : 32770.00:19:e2:53:8a:80
  Hello time                        : 2 seconds
  Maximum age                       : 20 seconds
  Forward delay                     : 15 seconds
  Local parameters
    Bridge ID                       : 32770.00:19:e2:53:8a:80
    Extended system ID              : 0
    Internal instance ID            : 2

STP bridge parameters for MSTI 3
  MSTI regional root                : 32771.00:19:e2:53:8a:80
  Hello time                        : 2 seconds
  Maximum age                       : 20 seconds
  Forward delay                     : 15 seconds
  Local parameters
    Bridge ID                       : 32771.00:19:e2:53:8a:80
    Extended system ID              : 0
    Internal instance ID            : 3

user@switchA# run show spanning-tree interface 

Spanning tree interface parameters for instance 0

Interface    Port ID    Designated      Designated         Port    State  Role
                         port ID        bridge ID          Cost
ge-0/0/0.0     128:513      128:513  32768.0019e25094a0     20000  FWD    ROOT
ge-0/0/1.0     128:514      128:514  32768.0019e2538a80     20000  FWD    DESG
ge-0/0/2.0     128:515      128:515  32768.0019e2538a80     20000  FWD    DESG
ge-0/0/3.0     128:516      128:516  32768.0019e2538a80     20000  FWD    DESG
ge-0/0/4.0     128:517      128:517  32768.0019e2538a80     20000  BLK    DIS 
ge-0/0/5.0     128:518      128:518  32768.0019e2538a80     20000  BLK    DIS 
ge-0/0/6.0     128:519      128:519  32768.0019e2538a80     20000  BLK    DIS 
ge-0/0/7.0     128:520      128:520  32768.0019e2538a80     20000  BLK    DIS 
ge-0/0/8.0     128:521      128:521  32768.0019e2538a80     20000  BLK    DIS 
ge-0/0/9.0     128:522      128:522  32768.0019e2538a80     20000  BLK    DIS 
ge-0/0/10.0    128:523      128:523  32768.0019e2538a80     20000  BLK    DIS 
ge-0/0/11.0    128:524      128:524  32768.0019e2538a80     20000  BLK    DIS 
ge-0/0/12.0    128:525      128:525  32768.0019e2538a80     20000  BLK    DIS 
ge-0/0/13.0    128:526      128:526  32768.0019e2538a80     20000  BLK    DIS 
ge-0/0/14.0    128:527      128:527  32768.0019e2538a80     20000  BLK    DIS 
ge-0/0/15.0    128:528      128:528  32768.0019e2538a80     20000  BLK    DIS 
ge-0/0/16.0    128:529      128:529  32768.0019e2538a80     20000  BLK    DIS 
ge-0/0/17.0    128:530      128:530  32768.0019e2538a80     20000  BLK    DIS 
ge-0/0/18.0    128:531      128:531  32768.0019e2538a80     20000  BLK    DIS 
ge-0/0/19.0    128:532      128:532  32768.0019e2538a80     20000  BLK    DIS 
ge-0/0/20.0    128:533      128:533  32768.0019e2538a80     20000  BLK    DIS 
ge-0/0/21.0    128:534      128:534  32768.0019e2538a80     20000  BLK    DIS 
ge-0/0/22.0    128:535      128:535  32768.0019e2538a80     20000  FWD    DESG
ge-0/0/23.0    128:536      128:536  32768.0019e2538a80     20000  FWD    DESG 

Spanning tree interface parameters for instance 1

Interface    Port ID    Designated      Designated         Port    State  Role
                         port ID        bridge ID          Cost
ge-0/0/22.0    128:535      128:535   4097.0019e2538a80     20000  FWD    DESG
ge-0/0/23.0    128:536      128:536   otherwise     20000  FWD    DESG

Spanning tree interface parameters for instance 2

Interface    Port ID    Designated      Designated         Port    State  Role
                         port ID        bridge ID          Cost
ge-0/0/22.0    128:535      128:535  32770.0019e2538a80     20000  FWD    DESG
ge-0/0/23.0    128:536      128:536  32770.0019e2538a80     20000  FWD    DESG

Spanning tree interface parameters for instance 3

Interface    Port ID    Designated      Designated         Port    State  Role
                         port ID        bridge ID          Cost
ge-0/0/22.0    128:535      128:535  32771.0019e2538a80     20000  FWD    DESG
ge-0/0/23.0    128:536      128:536  32771.0019e2538a80     20000  FWD    DESG

-----------------------------------------------

Debugging MST on the EX Switch:

To debug MST activity on EX switch, enable traceoptions on MSTP protocol:

[edit protocols mstp]
user@switchA# set traceoptions file mstp-debug world-readable    

[edit protocols mstp]
user@switchA# set traceoptions flag ?
Possible completions:
  all                  Trace all
  all-failures         Trace all failure conditions
  bpdu                 Trace BPDU reception and transmission
  bridge-detection-state-machine  Trace bridge detection state machine
  events               Trace events to the protocol state machine
  port-information-state-machine  Trace port information state machine
  port-migration-state-machine  Trace port migration state machine
  port-receive-state-machine  Trace port receive state machine
  port-role-select-state-machine  Trace port role selection state machine
  port-role-transit-state-machine  Trace port role transit state machine
  port-state-transit-state-machine  Trace port state transit state machine
  port-transmit-state-machine  Trace port transmit state machine
  ppmd                 Trace state and events for ppmd process
  state-machine-variables  Trace when state machine variables change
  timers               Trace protocol timers
  topology-change-state-machine  Trace topology change state machine


Once traceoption is setup, the activity can be monitor or viewed using the following command:

user@switchA# run file show /var/log/mstp-debug 

OR

user@switch!# run monitor start mstp-debug

 

Modification History:

2020-04-30: Minor changes in Solution section; article still valid and relevant

 

Comment on this article > Affected Products Browse the Knowledge Base for more articles related to these product categories. Select a category to begin.

Getting Up and Running with Junos

Getting Up and Running with Junos Security Alerts and Vulnerabilities Product Alerts and Software Release Notices Problem Report (PR) Search Tool EOL Notices and Bulletins JTAC User Guide Customer Care User Guide Pathfinder SRX High Availability Configurator SRX VPN Configurator Training Courses and Videos End User Licence Agreement Global Search