ExtremeSwitching (EXOS)

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ELRP or Spanning Tree for access port loop protection?

  • 1.  ELRP or Spanning Tree for access port loop protection?

    Posted 08-06-2020 13:51

    Do you use ELRP or Spanning Tree for access port loop protection? I have no mercy for spanning tree to build “redundant” networks. That should be done with CWDM, MLAG or stacks in my opinion and not with a protocol that was great in the 70’s and 80’s. What I need is a mechanism to prevent a user from causing a broadcast storm by looping two ports in a switch (or between switches). I have customers that use ELRP for this and it’s working quite well nowadays as ELRP has improved over the years. The downside is of course that adding another vendor’s equipment is impossible since no one else supports ELRP. That’s where spanning tree (purely) for access port loop protection comes in. What do you use? Any downsides for either method? Upsides?



  • 2.  RE: ELRP or Spanning Tree for access port loop protection?

    Posted 08-06-2020 13:59

    Fredrik,

    We use ELRP for loop protection.

    Depending on the customer’s preference we set it for either a permanent or 5 minute disable. Thought being that if someone plugs something in and it doesn't work they will move the cable to another drop so when the port gets enabled the loop will be gone. This allows things ports to function without user intervention which would be needed with a permanent disable. 

    Pro:

    • ELRP is easy to configure 
    • Simply works

    Con:

    • It is not state-full

     

     



  • 3.  RE: ELRP or Spanning Tree for access port loop protection?

    Posted 08-07-2020 07:24

    SpanTree only works when the connected device also uses STP, or do I miss something? If I plug a “dumb” switch to my EXOS switch and on the “dumb” switch is a loop… STP on the EXOS wouldn’t do anything.

    The problem with ELRP is that it uses multicast to check for loops and some devices block multicast. One of my customers has Aastra VoIP phones which have a second network port to attach a PC to the phone. Some users simply plug both ports of the phone to the network which causes a loop that is not detectable by ELRP.



  • 4.  RE: ELRP or Spanning Tree for access port loop protection?

    Posted 08-07-2020 12:20

    I see a lot of success ELRP blocking loops that run through third part switches, I also see STP blocking ports that run through devices that are not running STP because if the BPDU isn’t processed it is often just forwarded.

     



  • 5.  RE: ELRP or Spanning Tree for access port loop protection?

    Posted 08-07-2020 12:44

    Yes, we also use ELRP and it works fine in most cases. Except for those dumb phones that block the multicast traffic.

    And yes, if the dumb switch just forwards the BPDUs then STP should ofc work. But sadly not all switches do this.



  • 6.  RE: ELRP or Spanning Tree for access port loop protection?

    Posted 07-14-2021 16:27

    So is ELRP suitable for ISL links? I’m thinking it doesn’t operate in the same manner as STP as it doesn’t look at path cost or RootBridge Priority so yes in a larger network a loop maybe detected but potentially that would mean the port shutdown is closet to the core and not at the edge?  I’m a larger network you want the far end poorer costing link to be shutdown.
     

    can you mix ELRP and STP so that for instance STP is configured on Uplinks Only and Edge ports Configured to use ELRP only and not enabled excluded on uplinks anyway.

     

    input greatly appreciated as I have a customer who has a hub and spoke Topology and wants to interlink two spokes for resiliency.