Routing

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.