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Why are there two exact same path in BGP path?

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  • 1.  Why are there two exact same path in BGP path?

    Posted 04-10-2017 07:22

    Hi Please see the below bold highlighted output. 

     

    Can you explain why two exact same path exist( > to 6.74.102.96 via ae1.107)?

    In fact, there are two paths, one is " > to 6.74.102.96 via ae1.107", and second is  " to 6.74.102.98 via ae2.108"

     

     

     

    W>show route 98.24.176.208

     

    WAN.inet.0: 1483 destinations, 2688 routes (1825 active, 0 holddown, 9 hidden)
    + = Active Route, - = Last Active, * = Both

    98.24.176.208/31 *[BGP/170] 6w0d 03:36:04, localpref 100, from 6.74.102.98
    AS path: 2314 2314 I
    > to 6.74.102.96 via ae1.107
       to 6.74.102.98 via ae2.108
    [BGP/170] 5w0d 04:19:18, localpref 100
    AS path: 2314 2314 I
    > to 6.74.102.96 via ae1.107

     

     

     



  • 2.  RE: Why are there two exact same path in BGP path?
    Best Answer

     
    Posted 04-10-2017 07:51

    Hi,

     

    It depicts ECMP for the particular route ..

     

     

    You might have enabled multipath for your ebgp peer or group  and also there exists multiple equal cost path for the mentioned prefix:

     

    Sample Command for enabling multipath:

     

    set protocols bgp group external multipath.

     

     



  • 3.  RE: Why are there two exact same path in BGP path?

    Posted 04-10-2017 07:53

    Hello,

    Do You have "multipath" configured?

    If yes, this is how JUNOS displays multipath-enabled routes: "show route 98.24.176.208/31 extensive" will reveal more detailed information but the essence is below

    98.24.176.208/31 *[BGP/170] 6w0d 03:36:04, localpref 100, from 6.74.102.98
    AS path: 2314 2314 I
    > to 6.74.102.96 via ae1.107 <==== multipath contributor A (not best)
       to 6.74.102.98 via ae2.108 <==== multipath contributor B, best
    [BGP/170] 5w0d 04:19:18, localpref 100
    AS path: 2314 2314 I
    > to 6.74.102.96 via ae1.107 <======= multipath contributor A, not best

    Confusing, I know, but You'd get used to it eventually.

    HTH

    Thx

    Alex