Switching

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  • 1.  MSTP - Bridge Priority Question

    Posted 07-27-2014 15:57

    Hello,

     

         I have four Ex Switches (two 4200 and two 2200) connected on a ring topology, and I'm testing MSTP functionality. I configured several MSTI, but the issue I'm having happens with every one of them, so for the sake of simplicity I'll talk about only one here.

     

    This is, basically, my topology:

     

         S1----------S2

           |                 |

           |                 |

         S4----------S3 

     

         S1 has a bridge-priority of 0

         S2 has a bridge-priority of 4

         S3 has a bridge-priority of 8

         S4 has a bridge-priority of 16

     

         However, in both S3 and S4, when I check the priority with the "show spanning-tree interfaces" command, some interfaces have different values:

     blablablamstp.png

     

     Here is the configuration for S4:

     

    mstp {
      configuration-name Anillo-MSTP-1;
      interface ge-0/0/46.0 {
        mode point-to-point;
      }
      interface ge-0/0/47.0 {
        mode point-to-point;
      }
      msti 1 {
        bridge-priority 16k;
        vlan [ 10 20 ];
      }
    }

     

    Is this normal? Am I missing something here? I've searched a lot but didn't find anything very useful on the matter. Any help would be much apreciated.

     

    Thank you very much, I'm sorry for my English!

    Best regards,

    Antonela, from Argentina


    #junosexmstpbridgepriority


  • 2.  RE: MSTP - Bridge Priority Question

    Posted 07-27-2014 20:51

    Normal, very normal. The bridge ID will be different for each switch andthey better be:). The bridge ID is the bridge priority plus the MAC address of the bridge. That is what uniquely identifies each switch in the STP topology. "show spanning-tree bridge will show the root-id which should be different per the vlan to msti instance mapping

    Anyways why do you need to configure MSTP in this topology? MSTP feature was designed for use in a common Layer 2 network that have the Access switch layer seperate from teh aggregation layer. So what benefit that MSTP offers that you are looking to utilize? ERPS after all is a replacement for spanning tree when you have the Topology like yours. the eature I think you are looking for is available on the MX 3D series, where you can configure ultiple rings. But I stand corrected.



  • 3.  RE: MSTP - Bridge Priority Question

    Posted 07-28-2014 12:22

         First of all, thanks for your reply. 🙂

     

         I understand that the bridge ID is the priority + the MAC address. But if I set the priority to 16k, why does it show 8193.80711fe7cb41, as if it would have 8k configured?

     

         Also, I've been searching the Juniper documentation a lot, but I couldn't find detailed information on what all the fields of the "show spanning-tree interfaces" command actually show, like for example what's the difference between "Port ID" and "Designated port ID". Could you point me to any well documented site detailing the SP commands?

     

         As for the why, I understand that ERPS is better for this topology, in fact I'm doing this test presicely to compare the two protocols and give some practical evidence of them to a client.

     

         Thanks again!



  • 4.  RE: MSTP - Bridge Priority Question

    Posted 07-28-2014 12:45

    8193.80711fe7cb41 is the bridge ID of the designated bridge for that segment, I presume that ID is switch3, and I presume that's the link between switch 3 and 4, and 3 is designated because it has a lower ID because you set the priority to 8k on it.



  • 5.  RE: MSTP - Bridge Priority Question
    Best Answer

    Posted 07-28-2014 12:49

    Sorry for the patchwork reply. Unable to dedicate the full time.

    The port 47 is your root port which is connected to S3 is showing the bridge ID of S3.

    80711fe7cb41 is the MAC address of S3.



  • 6.  RE: MSTP - Bridge Priority Question

    Posted 07-28-2014 19:54

    Show spanning tree output

    http://www.juniper.net/techpubs/en_US/junos13.3/topics/reference/command-summary/show-spanning-tree-interface-spanning-trees-ex-series.html

     

    To achieve the loadbalancing ou are looking for would require configuring multile rings. With traffic fro a set a vlans going in one direction whill traffic for another set blocked ad vice versa. ERPS is far more efficient that RSTP, VSTP, MSTP. They have a lot more buit in overheads.



  • 7.  RE: MSTP - Bridge Priority Question

    Posted 07-31-2014 14:00

    Thank you for the replies and the explanation!

     

    I've managed to solve the issue, and now the ring is behaving as expected on the MSTI 1.

     

    However, now I have another problem: I've configured S1 to be my root switch on MSTI 1 (with a bridge priority of 0, hence having only the MAC address). But on MSTI 2, the root is suposed to be S2, again with a priority of 0 (S1 has a priority of 4k on MSTI 2). Despite this configuration, S1 is the root bridge on both MSTI, what am I missing here?

     

    S1 configuration:
        mstp {
            configuration-name Anillo-MSTP-1;
            bridge-priority 0;
            [...]
            msti 1 {
                bridge-priority 0;
                [...]
            }
            msti 2 {
                bridge-priority 4k; -----> This switch has a higher priority than S2, but it still takes the role of root bridge on this instance
                [...]
            }
        }

     

     

    S2 configuration:
        mstp {
            configuration-name Anillo-MSTP-1;
            bridge-priority 4k;
            [...]
            msti 1 {
                bridge-priority 4k;
                [...]
            }
            msti 2 {
                bridge-priority 0; -----> Despite having the lowest bridge priority of all 4 switches on this MSTI, S1 still takes the role of root bridge
                [...]
            }
        }

     

    Thanks for the help!



  • 8.  RE: MSTP - Bridge Priority Question

    Posted 07-31-2014 16:29

    That maybe that is a "feature" of configuring MSTP on ERPS.

    Can you post these output form the switches?

    show spanning-tree interface

    show spanning-tree bridge

     Maybe what you are noticing is that it is the regional root and the root bridge also.

    The following command should be the same on all switches, if not, then MSTP is misconfigured.

    > show spanning-tree mstp configuration

    ...
    Region name            : Region-1
    Revision               : 1
    Configuration digest   : 982jfmnj447gft667ww22abc77catop110

     

    Maybe the feature is configurable on the switch and will work to a certain degree, but unknown effects. As far as I can tell ERPS was designed for the MX series. I checked the feature explorer guide and it does not mention the EX so maybe the EX is not mature to handle all the features? Dunno, just guesing here

     

    Take a look at the feature support guide:

    http://pathfinder.juniper.net/feature-explorer/search-features.html#

    Platform/Application
    Introduced Release
    Prerequisites
    MX240
    Junos OS 10.2R1
    MX480
    Junos OS 10.2R1
    MX960
    Junos OS 10.2R1
    MX2010
    Junos OS 12.3R2
    MX2020
    Junos OS 12.3R1
    PDN Gateway (PGW)
    Junos OS 11.2W
    Serving Gateway (SGW)
    Junos OS 11.2W

     



  • 9.  RE: MSTP - Bridge Priority Question

    Posted 08-05-2014 12:56
    Thank you very much for your support! The problem was that I failed to add a line configuration in the name of region, has helped me with useful "sh spanning tree mstp configuration" command. Thanks again. Regards, Antonela.