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Router advertise route with LP of 4294967294

  • 1.  Router advertise route with LP of 4294967294

    Posted 03-23-2023 04:06

    Hi Team,

    I have a simple topology:

    • R1, R2, R3 are configured ospf, ldp, mpls full, they can see loopback of each other in inet.0 (by ospf) and in inet.3 (by ldp)
    • R2 has LSP to R4 --> R2 see lo0 of R4 in inet.3 by RSVP
    • R1 has BGP to R2, R4 has BGP to R2
    • R2 has BGP to R1 in group TO_R1 and R2 is RR of R1
    • R2 has BGP to R4 in group TO_R4
    • R4 advertises its lo0 from table inet.3 to R2 using BGP-LU

    [edit]
    juniper@R4# show policy-options policy-statement export_lo0_inet3 
    Mar 23 07:54:05
    term 1 {
        from {
            rib inet.3;
            route-filter 4.4.4.4/32 exact;
        }
        then accept;
    }

    R2 receives lo0 of R4 in the inet.3 then advertise to R1 by default.

    juniper@R2# run show route 4.4.4.4/32 
    Mar 23 07:57:59

    inet.0: 33 destinations, 33 routes (32 active, 0 holddown, 1 hidden)
    + = Active Route, - = Last Active, * = Both

    4.4.4.4/32         *[OSPF/10] 1w1d 21:09:01, metric 1
                        >  to 192.168.13.4 via ae0.0

    inet.3: 6 destinations, 9 routes (6 active, 0 holddown, 0 hidden)
    + = Active Route, - = Last Active, * = Both

    4.4.4.4/32         *[RSVP/7/1] 1d 13:26:06, metric 1
                        >  to 192.168.13.4 via ae0.0, label-switched-path R2_TO_R4
                        [LDP/9] 1w1d 21:09:01, metric 1
                        >  to 192.168.13.4 via ae0.0, Push 0
                        [BGP/170] 23:23:25, localpref 100, from 4.4.4.4
                          AS path: I, validation-state: unverified
                        >  to 192.168.13.4 via ae0.0, label-switched-path R2_TO_R4

    By default, R2 will advertise route 4.4.4.4/32 to R1 with LP = 100.

    [edit]
    juniper@R2# run show route advertising-protocol bgp 1.1.1.1 4.4.4.4/32 
    Mar 23 07:59:32

    inet.3: 6 destinations, 9 routes (6 active, 0 holddown, 0 hidden)
      Prefix                  Nexthop              MED     Lclpref    AS path
      4.4.4.4/32              4.4.4.4                      100        I

    [edit]
    juniper@R2# run show route advertising-protocol bgp 1.1.1.1 4.4.4.4/32 detail 
    Mar 23 07:59:37

    inet.3: 6 destinations, 9 routes (6 active, 0 holddown, 0 hidden)
      4.4.4.4/32 (3 entries, 2 announced)
     BGP group TO_R1 type Internal
         Route Label: 3
         Nexthop: 4.4.4.4
         Localpref: 100
         AS path: [100] I 
         Cluster ID: 2.2.2.2
         Originator ID: 4.4.4.4

    But if I configured an export policy in R2 to advertise route to R1 like the below, I see that R2 will advertise route 4.4.4.4/32 to R1 with LP = 4294967294. 

    [edit]
    juniper@R2# show policy-options policy-statement EXPORT_TO_R1_INET3              
    Mar 23 08:01:45
    term 1 {
        from {
            rib inet.3;
            route-filter 4.4.4.4/32 exact;
        }
        then accept;
    }

    [edit]
    juniper@R2# show protocols bgp group TO_R1                                       
    Mar 23 08:01:48
    type internal;
    local-address 2.2.2.2;
    family inet {
        labeled-unicast {
            rib {
                inet.3;
            }
        }
        unicast;
    }
    family inet-vpn {
        unicast;
    }
    export EXPORT_TO_R1_INET3;
    cluster 2.2.2.2;
    neighbor 1.1.1.1;

    [edit]
    juniper@R2# run show route advertising-protocol bgp 1.1.1.1 4.4.4.4/32           
    Mar 23 08:03:00

    inet.3: 6 destinations, 9 routes (6 active, 0 holddown, 0 hidden)
      Prefix                  Nexthop              MED     Lclpref    AS path
    * 4.4.4.4/32              Self                 1       4294967294 I

    [edit]
    juniper@R2# run show route advertising-protocol bgp 1.1.1.1 4.4.4.4/32 detail    
    Mar 23 08:03:02

    inet.3: 6 destinations, 9 routes (6 active, 0 holddown, 0 hidden)
    * 4.4.4.4/32 (3 entries, 1 announced)
     BGP group TO_R1 type Internal
         Route Label: 300608
         Nexthop: Self
         Flags: Nexthop Change
         MED: 1
         Localpref: 4294967294
         AS path: [100] I 
         Entropy label capable

    Can anyone help me explain this behavior?

    Thank you.



    ------------------------------
    Harry
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