Routing

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  • 1.  OSPF with same metric on two interfaces

    Posted 04-20-2021 18:00
    Dear Community,

    I have a serious and urgent query , my srx is connected through ospf (p2p) with my junos qfx primary and secondary both have same equal metrics.

    Whenever we run a trace from srx it always show traffic routed from secondary qfx and when show route it appears both ip address of primary and secondary qfx in "show route" but secondary ip have this sign ">" in front of it...as i have known that in juniper if equal metric then there should be load balancing in round robin fashion.

    Kindly help me to clear my these two concepts 
    1-why trace always shows secondary path,while having same cost of both primary and secondary?
    2-why "show route" have > sign in front of secondary ?

    Please help

    ------------------------------
    SYED SAFWAN ALI ZAIDI
    ------------------------------


  • 2.  RE: OSPF with same metric on two interfaces

     
    Posted 04-21-2021 01:48
    Because AFAIK it will not load balance automatically over equal paths. 

    You can enable this behavior with:
    set policy-options policy-statement ECMP then load-balance per-packet
    set routing-options forwarding-table export ECMP
    ​


    https://www.juniper.net/documentation/us/en/software/junos/sampling-forwarding-monitoring/topics/concept/policy-configuring-per-packet-load-balancing.html




  • 3.  RE: OSPF with same metric on two interfaces

    Posted 04-21-2021 05:06
    Okay ,i understand that point but how can it select between two paths ,which one is best path when both have same costs.

    ------------------------------
    SYED SAFWAN ALI ZAIDI
    ------------------------------



  • 4.  RE: OSPF with same metric on two interfaces

     
    Posted 04-21-2021 05:39

    It appears that this seletion is random:


    https://www.juniper.net/documentation/us/en/software/junos/routing-overview/topics/concept/routing-protocols-route-preferences-overview.html




  • 5.  RE: OSPF with same metric on two interfaces

    Posted 04-21-2021 08:41
    the > sign is an indication of the forwarding path. If you are attempting to load balance over two "equal" cost paths (p2p ospf), then why is it important to select a specific next hop? Im trying to understand the problem. that said, if one path is preferred over another simply cost down ospf metric on that link to make it the "better" route, which in that situation there will be no  load balancing