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Latest post 01-13-2017 8:12 PM by Martinl. 5 replies.
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  • 01-08-2017 5:34 PM

    Dual-home PEs importing their own RT back to CE?

    link in SP track but maybe should be here, anyway

     

    is there a benefit and disadvantages to importing its own RT back to CE?

    like in dual-home settup with R1 and R2 as CE in AS X;

    Ra and Rb as PE in SP area; R1 links with Ra and R2 with Rb.

    PE routers Ra and Rb have same RD and exporting RT a:a and importing back RT a:a. Do we really need  import a:a?

    What if change RD of Ra and b to be different?

    • Post Points: 5
  • 01-10-2017 6:50 PM In reply to

    Re: Dual-home PEs importing their own RT back to CE?

    it seems that number of routes is duplicated on PE. Ra puts Rb routes under its RD.  new routes are exact copy of what was already there but next-hop is via Rb (internal). stll Ra preffers external routes to R1, CE. 

    • Post Points: 20
  • 01-11-2017 3:59 PM In reply to

    • JoeM
    • Top 10 Contributor
    • Joined on 04-15-2012
    • Guadalajara, Mexico
    • Elite
    • Points 31,005

    Re: Dual-home PEs importing their own RT back to CE?

    Hi Martin,

    I am trying to follow what you are seeing.   Output?

    A BGP expert like Peety can give a better answer, and I would love to hear the advantages/disadvantages.   I don't see a problem with the export/imports being the same for CE's within a single customer's network -- especially if there are not a lot of prefixes being traded between sites.

    I have seen customers where the CE's have the same RT export/import.  I have always thought of this as simplicity or just not allocating numerous AS numbers for smaller sites.   Of course  Allow-AS or AS-Override is needed to allow the imports.

    • Post Points: 20
  • 01-11-2017 8:53 PM In reply to

    Re: Dual-home PEs importing their own RT back to CE?

    it looks like double redunndancy to me and not needed.  R1 is already backup to R2 and vice versa.  if R1 is importing its own routes back into AS , R2 sees them as duplicates.  and vice versa.

    i will try to lab this

    • Post Points: 20
  • 01-12-2017 10:32 AM In reply to

    • JoeM
    • Top 10 Contributor
    • Joined on 04-15-2012
    • Guadalajara, Mexico
    • Elite
    • Points 31,005

    Re: Dual-home PEs importing their own RT back to CE?

    If you are only dealing with a single CE, I cannot think of a scenario where there is an advantage to importing the same RT (from and to same CE device).  

    But by default, it still should not be an issue, because the CE should not import routes when it sees its own AS number. The commands allow-as or as-override would be explicit commands that would only be used if there were remote sites with the same AS, right?

     

     

    • Post Points: 20
  • 01-13-2017 8:12 PM In reply to

    Re: Dual-home PEs importing their own RT back to CE?

    yes, as-override is configured nad neighbor SOO X:Y  on provider side must be to avoid loops.

    • Post Points: 5
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