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RSVP LSP vs LDP Route Preference Behavior in Junos

  • 1.  RSVP LSP vs LDP Route Preference Behavior in Junos

    Posted 12 days ago

    Hello,

    I am trying to understand how Junos decides between RSVP and LDP when using the preference parameter on an RSVP LSP.

    Here is an example of the configuration:

    


    

    

    bash
    

    

    set protocols mpls label-switched-path silver_lsp_to_pe2 to 100.64.0.51
set protocols mpls label-switched-path silver_lsp_to_pe2 revert-timer 20
set protocols mpls label-switched-path silver_lsp_to_pe2 preference 6
set protocols mpls label-switched-path silver_lsp_to_pe2 primary silver
set protocols mpls label-switched-path silver_lsp_to_pe2 secondary best-effort-2 preference 7
set protocols mpls label-switched-path silver_lsp_to_pe2 secondary best-effort-2 standby
set protocols mpls label-switched-path silver_lsp_to_pe2 secondary best-effort-1 preference 9
set protocols mpls label-switched-path silver_lsp_to_pe2 secondary best-effort-1 standby
set protocols mpls label-switched-path silver_lsp_to_pe2 secondary best-effort-3 preference 8
set protocols mpls label-switched-path silver_lsp_to_pe2 secondary best-effort-3 standby

    Path preferences:

    • Primary path: preference 6

    • 1st secondary: preference 7

    • 2nd secondary: preference 8

    • 3rd secondary: preference 9

    If the first three paths fail, I end up with an RSVP LSP with preference 9.
    LDP is also enabled, with its default preference 9.

    In this situation, the route selected in the RIB is the LDP route instead of the RSVP one, even though both have the same preference. The knob bgp-igp-both-ribs is enabled.

    Routing table extract:

    


    

    

    bash
    

    

    inet.0: 94 destinations, 112 routes (93 active, 0 holddown, 1 hidden)
+ = Active Route, - = Last Active, * = Both

100.64.0.51/32     *[LDP/9] 00:16:44, metric 900
                      to 100.101.0.5 via ae0.10000
                      to 100.101.30.5 via ae0.10200
                    > to 100.101.40.5 via ae0.10300
                      to 10.200.10.1 via ae10.10000
                      to 10.200.11.1 via ae11.10000
                      to 10.200.12.1 via ae12.10000
                      to 10.200.13.1 via ae13.10000
                      to 10.200.14.1 via ae14.10000
                    [RSVP/9/1] 00:16:44, metric 900
                    > to 100.101.20.5 via ae0.10100, label-switched-path silver_lsp_to_pe2
                    [OSPF/10] 00:23:38, metric 900
                      to 100.101.0.5 via ae0.10000
                      to 100.101.30.5 via ae0.10200
                    > to 100.101.40.5 via ae0.10300
                      to 10.200.10.1 via ae10.10000
                      to 10.200.11.1 via ae11.10000
                      to 10.200.12.1 via ae12.10000
                      to 10.200.13.1 via ae13.10000
                      to 10.200.14.1 via ae14.10000

    Question:
    Why does Junos select the LDP route instead of the RSVP LSP when both have the same preference (9)?
    Is there a specific tie‑breaker or protocol hierarchy between LDP and RSVP in this case, and is there a recommended way to ensure the RSVP LSP is preferred when active?



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    Best Regards,
    ABDELHAMID
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